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Severe negative energy balance during 21 d at high altitude decreases fat-free mass regardless of dietary protein intake: a randomized controlled trial

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Abstract

In this 2-phase randomized controlled study, we examined whether consuming a higher-protein (HP) diet would attenuate fat-free mass (FFM) loss during energy deficit (ED) at high altitude (HA) in 17 healthy males (mean ± sd: 23 ± 6 yr; 82 ± 14 kg). During phase 1 at sea level (SL, 55 m), participants consumed a eucaloric diet providing standard protein (SP; 1.0 g protein/kg,) for 21 d. During phase 2, participants resided at HA (4300 m) for 22 d and were randomly assigned to either an SP or HP (2.0 g protein/kg) diet designed to elicit a 40% ED. Body composition, substrate oxidation, and postabsorptive whole-body protein kinetics were measured. Participants were weight stable during SL and lost 7.9 ± 1.9 kg ( P < 0.01) during HA, regardless of dietary protein intake. Decrements in whole-body FFM (3.6 ± 2.4 kg) and fat mass (3.6 ± 1.3 kg) were not different between SP and HP. HP oxidized 0.95 ± 0.32 g protein/kg per day more than SP and whole-body net protein balance was more negative for HP than for SP ( P < 0.01). Based on changes in body energy stores, the overall ED was 70% (-1849 ± 511 kcal/d, no group differences). Consuming an HP diet did not protect FFM during severe ED at HA.-Berryman, C. E., Young, A. J., Karl, J. P., Kenefick, R. W., Margolis, L. M., Cole, R. E., Carbone, J. W., Lieberman, H. R., Kim, I.-Y., Ferrando, A. A., Pasiakos, S. M. Severe negative energy balance during 21 d at high altitude decreases fat-free mass regardless of dietary protein intake: a randomized controlled trial.

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... The effect of protein intake above the current recommended safe level of intake (0·83 g/kg/d) on muscle mass maintenance under negative energy balance has been well documented (100,102,109) . Evidence indicates that, whilst amino acids contribute more to energy production at negative energy balance (105,110) , they are utilised more for de novo protein synthesis when energy balance is achieved. However, evidence is scarce in healthy older individuals, and it is unclear whether increased protein intake during negative energy balance is sufficient to maintain whole-body and muscle protein mass in healthy older adults. ...
... In contrast, limited knowledge is currently available on the impact of positive energy balance on the regulation of protein turnover rates and muscle mass in healthy older adults. Nonetheless, based on knowledge from energy deficit studies (105,110) as well as studies by Woolfson (111) and Calloway and Spector (98) , it can be assumed that positive energy balance reduces amino acid oxidation. Accordingly, exogenous amino acids (dietary protein) under such conditions are more efficiently utilised to achieve net positive protein balance. ...
... (b) and (c) indicate a negative energy balance condition. (b) The column shows the protein intake at the safe level of intake, but amino acid oxidation and urea excretion are increased under a negative energy balance condition, leading to negative whole-body net protein and nitrogen balance during negative energy balance (105,110) . (c) The column demonstrates that an increased protein intake (>0·83 g/kg/d) preserves whole-body net protein and nitrogen balance whilst increasing amino acid oxidation and urea excretion under a negative energy balance condition (104,107,108) . ...
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Article
Adequate protein intake is essential for the maintenance of whole-body protein mass. Different methodological approaches are used to substantiate the evidence for the current protein recommendations, and it is continuously debated whether older adults require more protein to counteract the age-dependent loss of muscle mass, sarcopenia. Thus, the purpose of this critical narrative review is to outline and discuss differences in the approaches and methodologies assessing the protein requirements and, hence, resulting in controversies in current protein recommendations for healthy older adults. Through a literature search, this narrative review first summarises the historical development of the Food and Agriculture Organization/World Health Organization/United Nations University setting of protein requirements and recommendations for healthy older adults. Hereafter, we describe the various types of studies (epidemiological studies and protein turnover kinetic measurements) and applied methodological approaches founding the basis and the different recommendations with focus on healthy older adults. Finally, we discuss important factors to be considered in future studies to obtain evidence for international agreement on protein requirements and recommendations for healthy older adults. We conclude by proposing future directions to determine ‘true’ protein requirements and recommendations for healthy older adults.
... In recent years, there has been a revitalized interest in characterizing the mechanisms by which environmental extremes affect metabolism with the goal of leveraging that information to optimize dietary intake, attenuate physiological decline, and sustain physical performance. Our laboratory has conducted studies to refine dietary protein and carbohydrate requirements to limit lean body mass loss and enhance performance in military personnel exposed to periods of severe energy deficit during cold-weather training operations (74,75) and high-altitude sojourns (10,132). The role of environmental stress, such as high altitude (42,43,88,89) and heat exposure (56,57), on energy substrate metabolism during exercise has also been explored to determine the possible ergogenic benefits of carbohydrate ingestion on performance. ...
... In recent years, our laboratory has published a series of articles from a well-controlled exercise and diet intervention study attempting to refine dietary recommendations for military operations conducted at high altitude (10,60,61,72,132). The primary objective of our study was to determine whether current protein recommendations for military personnel exposed to high TDEEs and resultant energy deficits effectively spared lean body mass during 21 days of severe energy deficit and continuous residence at 4,300 m (29,92). ...
... (Changes may still occur before final publication.) that the additional protein consumed in the high-protein group was used predominantly as an energy source during the 21 days of energy deficit at high altitude (10). We also demonstrated that acute high-altitude exposure inhibits the muscle anabolic signaling response to exercise (72). ...
Article
Dietary guidelines are formulated to meet minimum nutrient requirements, which prevent deficiencies and maintain health, growth, development, and function. These guidelines can be inadequate and contribute to disrupted homeostasis, lean body mass loss, and deteriorated performance in individuals who are working long, arduous hours with limited access to food in environmentally challenging locations. Environmental extremes can elicit physiological adjustments that alone alter nutrition requirements by upregulating energy expenditure, altering substrate metabolism, and accelerating body water and muscle protein loss. The mechanisms by which the environment, including high-altitude, heat, and cold exposure, alters nutrition requirements have been studied extensively. This contemporary review discusses physiological adjustments to environmental extremes, particularly when those adjustments alter dietary requirements. Please see http://www.annualreviews.org/page/journal/pubdates for expected final online publication date for the Annual Review of Nutrition, Volume 40. 2020
... Data included in this Short Report were secondary analyses from a controlled feeding and exercise study that assessed the effects of high protein diets on body composition during sustained energy deficit at HA [12]. This study (clinical trials.gov: ...
... The experimental design has been reported extensively [12][13][14][15][16]. In brief, the study was conducted over 43 consecutive days. ...
... During HA, participants were under constant supervision, performed daily exercise, and consumed either standard protein (mean ± SD; 1.1 ± 0.2 g/kg/d) or high protein (2.1 ± 0.2 g/kg/d), carbohydrate-matched, energy deficient diets (40%; 30% by energy restriction and 10% by exercise). Fat was the primary manipulated macronutrient during the energy deficit, such that the standard protein group consumed 1.1 ± 0.2 g/kg/d fat, and the high protein group consumed 0.7 ± 0.1 g/kg/d fat [12]. The diet intervention resulted in a 7.9 ± 1.9 kg loss of total body mass [13]. ...
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Background: The ergogenic effects of supplemental carbohydrate on aerobic exercise performance at high altitude (HA) may be modulated by acclimatization status. Longitudinal evaluation of potential performance benefits of carbohydrate supplementation in the same volunteers before and after acclimatization to HA have not been reported. Purpose: This study examined how consuming carbohydrate affected 2-mile time trial performance in lowlanders at HA (4300 m) before and after acclimatization. Methods: Fourteen unacclimatized men performed 80 min of metabolically-matched (~ 1.7 L/min) treadmill walking at sea level (SL), after ~ 5 h of acute HA exposure, and after 22 days of HA acclimatization and concomitant 40% energy deficit (chronic HA). Before, and every 20 min during walking, participants consumed either carbohydrate (CHO, n = 8; 65.25 g fructose + 79.75 g glucose, 1.8 g carbohydrate/min) or flavor-matched placebo (PLA, n = 6) beverages. A self-paced 2-mile treadmill time trial was performed immediately after completing the 80-min walk. Results: There were no differences (P > 0.05) in time trial duration between CHO and PLA at SL, acute HA, or chronic HA. Time trial duration was longer (P < 0.05) at acute HA (mean ± SD; 27.3 ± 6.3 min) compared to chronic HA (23.6 ± 4.5 min) and SL (17.6 ± 3.6 min); however, time trial duration at chronic HA was still longer than SL (P < 0.05). Conclusion: These data suggest that carbohydrate supplementation does not enhance aerobic exercise performance in lowlanders acutely exposed or acclimatized to HA. Trial registration: NCT, NCT02731066, Registered March 292,016.
... Furthermore, Norwegian men undergoing 7 days of field training lost an average of 4 kg of fat-free mass [9]. The loss of body protein during simulated combat operations is the result of altered protein kinetics that favor catabolism [10][11][12], which in turn may compromise performance [13]. We will use our previous investigations of critical care and severe stress to discuss potential mechanisms and strategies to combat muscle loss in military personnel during SUSOPS. ...
... A variety of anabolic agents have been investigated in burn patients, and it has been demonstrated that the administration and/or normalization of testosterone and/or its oral analogue, oxandrolone, growth hormone (GH), insulin, insulin-like growth factor (IGF)-1, and IGF-1 plus IGF-1 binding protein-3 (IGFBP3), will all improve muscle NB and mitigate the efflux of muscle amino acids [4]. Not surprisingly, these hormones have been shown to be altered by SUSOPS and military training [5,6,10,27], indicating a systemic amelioration of anabolic influence on skeletal muscle with increasing physiological stress. Despite the clinical success of the restoration and/or normalization of various hormonal effects, testosterone administration remains the most pragmatic, safe, and logistically feasible paradigm for consideration in military personnel. ...
... The MRE is designed to meet energy and nutrient requirements established by Army Regulation 40-25 if consumed as directed (i.e., 3 MRE per day,~3900 kcal, 127 g protein, 507 g carbohydrate, 152 g of fat; [40,41]). However, despite the ration's design and intended use, energy deficits and a suboptimal nutrient intake, as well as their associated consequences on muscle mass and whole-body protein, are largely inevitable during strenuous SUSOPS [10][11][12]39,42]. To date, several strategies have been employed to prevent energy deficits during military operations, including the provision of supplemental carbohydrate or protein [11], increasing the size and energy content of certain ration components (unpublished data), and pre-operational nutrition education [8]. ...
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Article
Military personnel may be exposed to circumstances (e.g., large energy deficits, sleep deprivation, cognitive demands, and environmental extremes) of external stressors during training and combat operations (i.e., operational stressors) that combine to degrade muscle protein. The loss of muscle protein is further exacerbated by frequent periods of severe energy deficit. Exposure to these factors results in a hypogonadal state that may contribute to observed decrements in muscle mass. In this review, lessons learned from studying severe clinical stressed states and the interventions designed to mitigate the loss of muscle protein are discussed in the context of military operational stress. For example, restoration of the anabolic hormonal status (e.g., testosterone, insulin, and growth hormone) in stressed physiological states may be necessary to restore the anabolic influence derived from dietary protein on muscle. Based on our clinical experiences, restoration of the normal testosterone status during sustained periods of operational stress may be advantageous. We demonstrated that in severe burn patients, pharmacologic normalization of the anabolic hormonal status restores the anabolic stimulatory effect of nutrition on muscle by improving the protein synthetic efficiency and limiting amino acid loss from skeletal muscle. Furthermore, an optimal protein intake, and in particular essential amino acid delivery, may be an integral ingredient in a restored anabolic response during the stress state. Interventions which improve the muscle net protein balance may positively impact soldier performance in trying conditions.
... The analyses reported herein were included as secondary objectives in a randomized, controlled feeding study that examined the effects of manipulating dietary protein on fat-free mass during HA sojourn ( Berryman et al. 2018). Participants were 17 young, healthy, physically active male SL natives ( Table 1). ...
... The study design has been reported in detail, previously ( Berryman et al. 2018;Young et al. 2018). Briefly, the study consisted of two phases conducted over 43 consecutive days. ...
... Further, Westergaard et al. (1970) observed that plasma albumin synthesis and breakdown rates remained unchanged in SL residents living at 3450 m for 8 days, but albumin content shifted from intravascular to extravascular space, while at the same time the rate of IgG breakdown was increased at HA. More recently, we have observed that whole body protein synthesis is decreased during chronic HA exposure ( Berryman et al. 2018). Thus, both decreased synthesis of plasma protein and leakage of plasma protein into the extravascular space could be contributing to a decrease in TCP during hypoxic exposure. ...
... Active exposures consisted primarily of trekking or mountaineering activity with only occasional cardiovascular-based endurance exercise of low-to moderateintensity. Fifteen studies manipulated food intake ( Table 1B), two of which applied a hypocaloric diet (Fulco et al., 2002;Berryman et al., 2017). The duration of altitude (or simulated altitude) exposure varied from 4 days to 16 weeks ( Table 1B). ...
... A significant decrease in body weight was observed in 14 of the 15 studies with dietary manipulation. Body weight reduction ranged from −7.7 to −0.01 kg in studies where energy intake was not manipulated, and from −7.2 to −6.6 kg where a hypocaloric diet was applied (Fulco et al., 2002;Berryman et al., 2017). Body weight decreased by −3.1 to −0.4 kg in studies where dietary supplements were given (Schena et al., 1992;Vats et al., 2007;Wing-Gaia et al., 2014) as well as studies with matched food intake (Holm et al., 2010;Debevec et al., 2014a,b) and increased energy intake (Surks et al., 1966;Consolazio et al., 1972;Bharadwaj and Malhotra, 1974;Butterfield et al., 1992;Mawson et al., 2000;Barnholt et al., 2006). ...
... Reductions in FFM varied between −3.9 to −0.2 kg and −2.1 to −0.1 kg in studies with active and passive exposures, respectively. FFM decreased by −2.4 to −0.4 kg when dietary intake was not manipulated (N = 5; including changes from control groups of dietary manipulated studies), and by −2.1 to −0.1 kg when intake was manipulated (N = 7) with the largest decreases (−4.6 to −3.3 kg) recorded in studies involving a hypocaloric diet (Fulco et al., 2002;Berryman et al., 2017). ...
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Article
Changes in body composition and weight loss frequently occur when humans are exposed to hypoxic environments. The mechanisms thought to be responsible for these changes are increased energy expenditure resulting from increased basal metabolic rate and/or high levels of physical activity, inadequate energy intake, fluid loss as well as gastrointestinal malabsorption. The severity of hypoxia, the duration of exposure as well as the level of physical activity also seem to play crucial roles in the final outcome. On one hand, excessive weight loss in mountaineers exercising at high altitudes may affect performance and climbing success. On the other, hypoxic conditioning is presumed to have an important therapeutic potential in weight management programs in overweight/obese people, especially in combination with exercise. In this regard, it is important to define the hypoxia effect on both body composition and weight change. The purpose of this study is to define, through the use of meta-analysis, the extent of bodyweight -and body composition changes within the three internationally classified altitude levels (moderate altitude: 1500–3500 m; high altitude: 3500–5300 m; extreme altitude: >5300 m), with emphasis on physical activity, nutrition, duration of stay and type of exposure.
... The analyses reported herein were included as secondary objectives in a randomized, controlled feeding study that examined the effects of manipulating dietary protein on fat-free mass during HA sojourn ( Berryman et al. 2018). Participants were 17 young, healthy, physically active male SL natives ( Table 1). ...
... The study design has been reported in detail, previously ( Berryman et al. 2018;Young et al. 2018). Briefly, the study consisted of two phases conducted over 43 consecutive days. ...
... Further, Westergaard et al. (1970) observed that plasma albumin synthesis and breakdown rates remained unchanged in SL residents living at 3450 m for 8 days, but albumin content shifted from intravascular to extravascular space, while at the same time the rate of IgG breakdown was increased at HA. More recently, we have observed that whole body protein synthesis is decreased during chronic HA exposure ( Berryman et al. 2018). Thus, both decreased synthesis of plasma protein and leakage of plasma protein into the extravascular space could be contributing to a decrease in TCP during hypoxic exposure. ...
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Article
When sea‐level (SL) residents rapidly ascend to high altitude (HA), plasma volume (PV) decreases. A quantitative model for predicting individual %∆PV over the first 7 days at HA has recently been developed from the measurements of %∆PV in 393 HA sojourners. We compared the measured %∆PV with the %∆PV predicted by the model in 17 SL natives living 21 days at HA (4300 m). Fasting hematocrit (Hct), hemoglobin (Hb) and total circulating protein (TCP) concentrations at SL and on days 2, 7, 13, and 19 at HA were used to calculate %∆TCP and %∆PV. Mean [95%CI] measured %∆PV on HA2, 7, 13 and 19 was −2.5 [−8.2, 3.1], −11.0 [−16.6, −5.5], −11.7 [−15.9, −7.4], and −16.8 [−22.2, −11.3], respectively. %∆PV and %∆TCP were positively correlated (P < 0.001) at HA2, 7, 13, and 19 (r2 = 0.77, 0.88, 0.78, 0.89, respectively). The model overpredicted mean [95% CI] decrease in %∆PV on HA2 (−12.5 [−13.9, −11.1]) and HA7 (−21.5 [−23.9, −19.1]), accurately predicted the mean decrease on HA13 (−14.3, [−20.0, −8.7]), and predicted a mean increase in %∆PV on HA19 (12.4 [−5.0, 29.8]). On HA2, 7, 13, and 19 only 2, 2, 6, and 1, respectively, of 17 individual measures of %∆PV were within 95% CI for predicted %∆PV. These observations indicate that PV responses to HA are largely oncotically mediated, vary considerably among individuals, and available quantitative models require refinement to predict %∆PV exhibited by individual sojourners. This investigation compared the changes in plasma volume measured in sea‐level natives sojourning at high altitude to the plasma volume changes predicted using a recently published quantitative model, which has not been externally validated. Our findings indicate that plasma volume changes during high‐altitude sojourn are largely oncotically mediated, vary considerably among individuals and are not well predicted by the previously published model.
... In contrast, supplementing ad libitum, higher-protein diets with additional high-quality protein did not alter body composition or whole-body net protein balance in US Marines in recovery from a 7-d, severe energy deficit (∼4200 kcal/d) (18). Similarly, doubling dietary protein intake (2.0 compared with 1.0 g · kg −1 · d −1 ) did not attenuate fat-free mass loss in healthy young men exposed to a ∼70% energy deficit (∼1840 kcal/d) for 21 d while acclimatizing to high altitude (4300 m) (24). ...
... Similarly, there were no observed differences in any measures between those volunteers consuming 2.0 or 1.0 g protein · kg −1 · d −1 , once more highlighting the importance of the overall magnitude of the energy deficit in modulating the benefits, or lack thereof, of higher-protein diets. With such a severe energy deficit, the doubling of protein intake (2.0 compared with 1.0 g protein · kg −1 · d −1 ) resulted in a parallel increase in protein oxidation (24), thereby limiting amino acid availability to support muscle protein turnover purposes. ...
... Similarly, consuming higher amounts of dietary protein (2.0 compared with 1.0 g · kg −1 · d −1 ) during a 21-d severe ∼70% energy deficit (∼1840 kcal/d) and accompanying high-altitude (4300 m) acclimatization resulted in significantly higher rates of postabsorptive protein oxidation (24). Net whole-body protein balance, however, was more negative for those consuming the higher-protein diet, again illustrating a potential inverse relation between higherprotein intakes during energy deficit and net protein balance. ...
Article
In a review published in 2012, we concluded that higher-protein diets preserve muscle mass during energy deficit via stimulated mammalian target of rapamycin complex 1 signaling, coincident increased muscle protein synthesis (PS), inhibited ubiquitin-mediated proteolysis, and suppressed muscle protein breakdown (PB). Since then, there have been significant advances in understanding the fundamental effects of higher-protein diets, with or without exercise training, on muscle and whole-body protein homeostasis during negative energy balance. Therefore, an update on the evolution of this field of research is warranted to better inform recommendations on best practices for healthy weight loss and muscle preservation. We will review the most recent studies examining the effects of higher-protein diets and negative energy balance on body composition, muscle PS, muscle PB, associated intracellular regulatory pathway activities, and whole-body protein homeostasis. In addition to critically analyzing contemporary findings, knowledge gaps and opportunities for continued research will be identified. Overall, the newest research confirms that consuming higher-protein diets, particularly when coupled with resistance exercise, preserves muscle mass and maintains whole-body protein homeostasis during moderate energy deficits (i.e., normal weight loss). However, these newer findings also indicate that as the magnitude of energy deficit increases, the efficacy of higher-protein diets for mitigating losses of fat-free mass is diminished. Further, recent results suggest that alterations in muscle PS, more so than muscle PB, may be primarily responsible for changes in muscle mass that occur in response to negative energy balance.
... Participants and study design. The analyses reported herein were included as secondary objectives in a randomized, controlled feeding study designed to examine the efficacy of a higher protein diet for preserving fat-free mass during HA sojourn (9). Participants were 17 healthy, unacclimatized, physically active men. ...
... Study methods have been previously reported in detail (9). Briefly, the study was a randomized, controlled trial consisting of two phases conducted over 43 consecutive days. ...
... Diets contained either a standard or higher amount of protein, and were designed to induce weight loss, which is common during HA sojourn (33). The estimated energy deficit at HA was 70% or 1,849 kcal/day (SD 511) (9). ...
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Hypobaric hypoxia, and dietary protein and fat intakes have been independently associated with an altered gastrointestinal (GI) environment and gut microbiota, but little is known regarding host-gut microbiota interactions at high altitude (HA) and the impact of diet macronutrient composition. This study aimed to determine the effect dietary protein:fat ratio manipulation on the gut microbiota and GI barrier function during weight loss at high altitude (HA), and to identify associations between the gut microbiota and host responses to HA. Following sea level (SL) testing, 17 healthy males were transported to HA (4300m) and randomly assigned to consume provided standard-protein (SP; 1.1g/kg/d, 39% fat) or higher-protein (HP; 2.1g/kg/d, 23% fat) carbohydrate-matched hypocaloric diets for 22d. Fecal microbiota composition and metabolites, GI barrier function, GI symptoms, and acute mountain sickness (AMS) severity were measured. Macronutrient intake did not impact fecal microbiota composition, had only transient effects on microbiota metabolites, and had no effect on increases in small intestinal permeability, GI symptoms, and inflammation observed at HA. AMS severity was also unaffected by diet, but in exploratory analyses was associated with higher SL relative abundance of Prevotella, a known driver of inter-individual variability in human gut microbiota composition, and greater microbiota diversity after AMS onset. Findings suggest that the gut microbiota may contribute to variability in host responses to HA independent of the dietary protein:fat ratio, but should be considered preliminary and hypothesis-generating due to the small sample size and exploratory nature of analyses associating the fecal microbiota and host responses to HA.
... Participants in this study were part of a larger randomized, controlled study that assessed the effects of standard (1.0 g/kg/d) versus higher (2.0 g/kg/d) protein diets on body composition in response to 21 days of negative energy balance at HA (Berryman et al., 2018). In brief, 17 recreationally active (programmed physical activity 2-4 d/week) men, aged 18-42 years who were not acclimatized to HA (i.e., born at altitudes < 2,100 m, currently residing at altitudes < 1,200 m, and who had not traveled to altitudes > 1,200 m for 5 days or more within 2 months before beginning the study) completed that parent study (Berryman et al., 2018). ...
... Participants in this study were part of a larger randomized, controlled study that assessed the effects of standard (1.0 g/kg/d) versus higher (2.0 g/kg/d) protein diets on body composition in response to 21 days of negative energy balance at HA (Berryman et al., 2018). In brief, 17 recreationally active (programmed physical activity 2-4 d/week) men, aged 18-42 years who were not acclimatized to HA (i.e., born at altitudes < 2,100 m, currently residing at altitudes < 1,200 m, and who had not traveled to altitudes > 1,200 m for 5 days or more within 2 months before beginning the study) completed that parent study (Berryman et al., 2018). To address whether AHA exposure, and acclimatization to HA, affected exogenous glucose oxidation during aerobic steady-state exercise, participants assigned to the standard (n = 8) and higher (n = 9) protein diets were further randomized to groups provided equal volumes of flavormatched carbohydrate (CHO; n = 9, 4 standard and 5 higher protein) and placebo (PLA; n = 8, 4 standard and 4 higher protein) drinks during exercise. ...
... The protein intake level was chosen based on mean ad libitum protein intakes in active duty military personnel (Margolis et al., 2012). TDEE was estimated from the sum of (a) measured resting metabolic rate (multiplied by 1.3 to account for activities of daily living and diet-induced thermogenesis) and (b) exercise-induced energy expenditure (EIEE) estimated from corresponding metabolic equivalents of activities reported in the 3 days physical activity log (Ainsworth et al., 2011;Berryman et al., 2018). Those TDEE estimates were then averaged with estimated TDEE requirements calculated using the Harris-Benedict equation (Roza and Shizgal, 1984). ...
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This study investigated how high-altitude (HA, 4300 m) acclimatization affected exogenous glucose oxidation during aerobic exercise. Sea-level (SL) residents (n = 14 men) performed 80-min, metabolically matched exercise ( V ˙ O2 ∼ 1.7 L/min) at SL and at HA < 5 h after arrival (acute HA, AHA) and following 22-d of HA acclimatization (chronic HA, CHA). During HA acclimatization, participants sustained a controlled negative energy balance (-40%) to simulate the "real world" conditions that lowlanders typically experience during HA sojourns. During exercise, participants consumed carbohydrate (CHO, n = 8, 65.25 g fructose + 79.75 g glucose, 1.8 g carbohydrate/min) or placebo (PLA, n = 6). Total carbohydrate oxidation was determined by indirect calorimetry and exogenous glucose oxidation by tracer technique with 13C. Participants lost (P ≤ 0.05, mean ± SD) 7.9 ± 1.9 kg body mass during the HA acclimatization and energy deficit period. In CHO, total exogenous glucose oxidized during the final 40 min of exercise was lower (P < 0.01) at AHA (7.4 ± 3.7 g) than SL (15.3 ± 2.2 g) and CHA (12.4 ± 2.3 g), but there were no differences between SL and CHA. Blood glucose and insulin increased (P ≤ 0.05) during the first 20 min of exercise in CHO, but not PLA. In CHO, glucose declined to pre-exercise concentrations as exercise continued at SL, but remained elevated (P ≤ 0.05) throughout exercise at AHA and CHA. Insulin increased during exercise in CHO, but the increase was greater (P ≤ 0.05) at AHA than at SL and CHA, which did not differ. Thus, while acute hypoxia suppressed exogenous glucose oxidation during steady-state aerobic exercise, that hypoxic suppression is alleviated following altitude acclimatization and concomitant negative energy balance.
... Participants were part of a larger randomized, controlled study that compared the effects of consuming higher-protein (2.0 g/kg/d) vs. standard-protein (1.0 g/ kg/d) diets on body composition responses with 21 d of energy deficit at HA (29). Participant eligibility and recruitment details are reported elsewhere (29). ...
... Participants were part of a larger randomized, controlled study that compared the effects of consuming higher-protein (2.0 g/kg/d) vs. standard-protein (1.0 g/ kg/d) diets on body composition responses with 21 d of energy deficit at HA (29). Participant eligibility and recruitment details are reported elsewhere (29). In brief, 17 recreationally active (programmed physical activity 2-4 d/wk) men, age 18-42 yr, who were not acclimatized to HA completed the parent study (29). ...
... Participant eligibility and recruitment details are reported elsewhere (29). In brief, 17 recreationally active (programmed physical activity 2-4 d/wk) men, age 18-42 yr, who were not acclimatized to HA completed the parent study (29). For experiments described in this report, data were obtained from 8 of those 17 participants who were not subjected to other nutritional interventions that had the potential to confound the anabolic and proteolytic signaling responses we were investigating. ...
Article
Muscle loss at high altitude (HA) is attributable to energy deficit and a potential dysregulation of anabolic signaling. Exercise and protein ingestion can attenuate the effects of energy deficit on muscle at sea level (SL). Whether these effects are observed when energy deficit occurs at HA is unknown. To address this, muscle obtained from lowlanders ( n = 8 males) at SL, acute HA (3 h, 4300 m), and chronic HA (21 d, -1766 kcal/d energy balance) before [baseline (Base)] and after 80 min of aerobic exercise followed by a 2-mile time trial [postexercise (Post)] and 3 h into recovery (Rec) after ingesting whey protein (25 g) were analyzed using standard molecular techniques. At SL, Post, and REC, p-mechanistic target of rapamycin (mTOR)Ser2448, p-p70 ribosomal protein S6 kinase (p70S6K)Ser424/421, and p-ribosomal protein S6 (rpS6)Ser235/236 were similar and higher ( P < 0.05) than Base. At acute HA, Post p-mTORSer2448 and Post and REC p-p70S6KSer424/421 were not different from Base and lower than SL ( P < 0.05). At chronic HA, Post and Rec p-mTORSer2448 and p-p70S6KSer424/421 were not different from Base and lower than SL, and, independent of time, p-rpS6Ser235/236 was lower than SL ( P < 0.05). Post proteasome activity was lower ( P < 0.05) than Base and Rec, independent of phase. Our findings suggest that HA exposure induces muscle anabolic resistance that is exacerbated by energy deficit during acclimatization, with no change in proteolysis.-Margolis, L. M., Carbone, J. W., Berryman, C. E., Carrigan, C. T., Murphy, N. E., Ferrando, A. A., Young, A. J., Pasiakos, S. M. Severe energy deficit at high altitude inhibits skeletal muscle mTORC1-mediated anabolic signaling without increased ubiquitin proteasome activity.
... We recently reported that consuming a controlled higher protein hypocaloric diet relative to a controlled standard- protein hypocaloric diet did not protect fat-free mass during weight loss over 22 days at HA ( Berryman et al., 2017). This report details changes in perceived appetite, appetite- mediating hormones, and food preferences measured as secondary outcomes during that study. ...
... The 43-day study included a 21-day sea level (SL) phase (50 m; Natick, MA), which was immediately followed by 22 days at HA (4300 m; Pikes Peak, CO) ( Berryman et al., 2017) (Fig. 1). Upon enrollment, investigators randomized participants using computer-generated randomization to consume a standard-protein or higher protein diet at HA. ...
... To induce a 40% total energy deficit, supervised low-to-moderate inten- sity exercise was conducted to increase physical activity expenditure by 10% of weight-maintenance energy needs. The duration and magnitude of the energy deficit were de- signed to replicate those used in a recent study from our group investigating the effects of varying protein intake on body composition during weight loss at SL ( Pasiakos et al., 2013aPasiakos et al., , 2013b and was in accord with the primary study objective of determining the efficacy of a higher protein diet for fat-free mass retention during weight loss at HA ( Berryman et al., 2017). This magnitude of energy deficit was within ranges reported during HA sojourns in which dietary intake was ad libitum (Hoyt et al., 1994;Westerterp et al., 1994) and was consistent with previous studies investigating endocrine re- sponses at HA ( Barnholt et al., 2006). ...
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Karl, J. Philip, Renee E. Cole, Claire E. Berryman, Graham Finlayson, Patrick N. Radcliffe, Matthew T. Kominsky, Nancy E. Murphy, John W. Carbone, Jennifer C. Rood, Andrew J. Young, and Stefan M. Pasiakos. Appetite Suppression and Altered Food Preferences Coincide with Changes in Appetite-Mediating Hormones During Energy Deficit at High Altitude, But Are Not Affected by Protein Intake. High Alt Med Biol. 00:000-000, 2018.-Anorexia and unintentional body weight loss are common during high altitude (HA) sojourn, but underlying mechanisms are not fully characterized, and the impact of dietary macronutrient composition on appetite regulation at HA is unknown. This study aimed to determine the effects of a hypocaloric higher protein diet on perceived appetite and food preferences during HA sojourn and to examine longitudinal changes in perceived appetite, appetite mediating hormones, and food preferences during acclimatization and weight loss at HA. Following a 21-day level (SL) period, 17 unacclimatized males ascended to and resided at HA (4300 m) for 22 days. At HA, participants were randomized to consume measured standard-protein (1.0 g protein/kg/d) or higher protein (2.0 g/kg/d) hypocaloric diets (45% carbohydrate, 30% energy restriction) and engaged in prescribed physical activity to induce an estimated 40% energy deficit. Appetite, food preferences, and appetite-mediating hormones were measured at SL and at the beginning and end of HA. Diet composition had no effect on any outcome. Relative to SL, appetite was lower during acute HA (days 0 and 1), but not different after acclimatization and weight loss (HA day 18), and food preferences indicated an increased preference for sweet- and low-protein foods during acute HA, but for high-fat foods after acclimatization and weight loss. Insulin, leptin, and cholecystokinin concentrations were elevated during acute HA, but not after acclimatization and weight loss, whereas acylated ghrelin concentrations were suppressed throughout HA. Findings suggest that appetite suppression and altered food preferences coincide with changes in appetite-mediating hormones during energy deficit at HA. Although dietary protein intake did not impact appetite, the possible incongruence with food preferences at HA warrants consideration when developing nutritional strategies for HA sojourn.
... High-protein diets have been used to improve skeletal muscle anabolism during eucaloric feeding and preserve lean mass during hypocaloric feeding (Morales et al., 2017;Pasiakos et al., 2015). However, these diets lack efficacy during the severe energy deficits often experienced by military personnel (Margolis et al., 2014(Margolis et al., , 2016Berryman et al., 2018), and alternative solutions are needed. Testosterone administration is one potential solution as the hormone acts in a dose-dependent fashion to increase anabolic balance, lean muscle mass, and muscular strength in healthy men (Bhasin et al., 1996(Bhasin et al., , 2001. ...
... Testosterone administration during exercise-and diet-induced severe energy deficit, and weight regain due to refeeding significantly influenced serum metabolomic signatures. Testosterone administration resulted in higher levels of androgenic steroid (i.e., 5alpha-androstan-3alpha, 17beta-diol monosulfate (Berryman et al., 2018), androsterone sulfate) and fatty acid metabolites (acylcarnitine, unsaturated fatty acids, medium chain fatty acids) and lower levels of amino acids metabolites (i.e., isovalerate [i5:0], isovalerylcarnitine [C5]) during severe energy deficit. However, these changes were transient and reversed during the recovery period when testosterone was not administered and energy deficit ended. ...
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Introduction Testosterone administration attenuates reductions in total body mass and lean mass during severe energy deficit (SED). Objectives This study examined the effects of testosterone administration on the serum metabolome during SED. Methods In a double-blind, placebo-controlled clinical trial, non-obese men were randomized to receive 200-mg testosterone enanthate/wk (TEST) (n = 24) or placebo (PLA) (n = 26) during a 28-d inpatient, severe exercise- and diet-induced energy deficit. This study consisted of three consecutive phases. Participants were free-living and provided a eucaloric diet for 14-d during Phase 1. During Phase 2, participants were admitted to an inpatient unit, randomized to receive testosterone or placebo, and underwent SED for 28-d. During Phase 3, participants returned to their pre-study diet and physical activity habits. Untargeted metabolite profiling was conducted on serum samples collected during each phase. Body composition was measured using dual-energy X-ray absorptiometry after 11-d of Phase 1 and after 25-d of Phase 2 to determine changes in fat and lean mass. Results TEST had higher (Benjamini–Hochberg adjusted, q < 0.05) androgenic steroid and acylcarnitine, and lower (q < 0.05) amino acid metabolites after SED compared to PLA. Metabolomic differences were reversed by Phase 3. Changes in lean mass were associated (Bonferroni-adjusted, p < 0.05) with changes in androgenic steroid metabolites (r = 0.42–0.70), acylcarnitines (r = 0.37–0.44), and amino acid metabolites (r = − 0.36–− 0.37). Changes in fat mass were associated (p < 0.05) with changes in acylcarnitines (r = − 0.46–− 0.49) and changes in urea cycle metabolites (r = 0.60–0.62). Conclusion Testosterone administration altered androgenic steroid, acylcarnitine, and amino acid metabolites, which were associated with changes in body composition during SED.
... The eligibility criteria was designed to recruit volunteers with characteristics that most closely reflect the characteristics of actual Soldiers. Previous published papers from our laboratory, including the OPS I study (which provided the rationale for the current study), have used similar exclusion criteria; the descriptive characteristics of participants recruited for the OPS I study [8] were comparable to those reported in our previous published studies in Soldiers [17][18][19]. While recruiting actual Soldiers with previous military experience would increase the practical applicability of the current intervention, the time commitment and requirements of this study (e.g., a ~2-month leave period under highly-controlled laboratory conditions) would make recruiting active-duty Soldiers highly unlikely and unrealistic. ...
... Study participants will undergo a 3-phase, 50-day study, consisting of 7 days of baseline testing and diet acclimation (Phase 1, days 1-7), 20 days of simulated SUSOPS (Phase 2, days [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], and 23 days of recovery (Phase 3, days 28-50) (Fig. 1). On day 8, after completing baseline testing and diet acclimation (Phase 1), participants will be randomized to receive either a single intramuscular injection of testosterone undecanoate (TEST; 750 mg, standard pharmaceutical dose [12]) or an iso-volumetric placebo (PLA, sesame oil solution). ...
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Background Previously, young males administered 200 mg/week of testosterone enanthate during 28 days of energy deficit (EDef) gained lean mass and lost less total mass than controls (Optimizing Performance for Soldiers I study, OPS I). Despite that benefit, physical performance deteriorated similarly in both groups. However, some experimental limitations may have precluded detection of performance benefits, as performance measures employed lacked military relevance, and the EDef employed did not elicit the magnitude of stress typically experienced by Soldiers conducting operations. Additionally, the testosterone administered required weekly injections, elicited supra-physiological concentrations, and marked suppression of endogenous testosterone upon cessation. Therefore, this follow-on study will address those limitations and examine testosterone's efficacy for preserving Solder performance during strenuous operations. Methods In OPS II, 32 males will participate in a randomized, placebo-controlled, double-blind trial. After baseline testing, participants will be administered either testosterone undecanoate (750 mg) or placebo before completing four consecutive, 5-day cycles simulating a multi-stressor, sustained military operation (SUSOPS). SUSOPS will consist of two low-stress days (1000 kcal/day exercise-induced EDef; 8 h/night sleep), followed by three high-stress days (3000 kcal/day and 4 h/night). A 23-day recovery period will follow SUSOPS. Military relevant physical performance is the primary outcome. Secondary outcomes include 4-comparment body composition, muscle and whole-body protein turnover, intramuscular mechanisms, biochemistries, and cognitive function/mood. Conclusions OPS II will determine if testosterone undecanoate safely enhances performance, while attenuating muscle and total mass loss, without impairing cognitive function, during and in recovery from SUSOPS. Trial Registration ClinicalTrials.gov Identifier: NCT04120363.
... 35 In humans, only newborns show clear hypoxic hypometabolism. 36 Adult humans acutely exposed to hypoxia rather show an increase in RMR in most studies [37][38][39][40][41][42] but not all. 43 The origin of this increase in RMR is still unclear; increased cardiorespiratory work, increased sympathetic activity, increased circulating interleukin-6 (IL-6) levels, and increased thyroid activity may all play a role. ...
... However, in the context of the management of obesity, given the frequent comorbidities, exposure to such extreme altitudes/hypoxia would seem hazardous, in particular because the loss of muscle mass is difficult to prevent, even when combining physical activity and high protein intake. 37 But there is potentially a threshold below which the effect of hypoxic exposure on muscle loss is limited. 64 With a certain reserve with regard to the potential effects of exposure to safer lower altitudes/levels of hypoxia over shorter periods, there is clear evidence for reduced appetite in conditions of hypoxia, but the underlying mechanisms remain to be better understood. ...
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Because of the enduring rise in the prevalence of obesity worldwide, there is continued interest in hypoxia as a mechanism underlying the pathophysiology of obesity and its comorbidities and as a potential therapeutic adjunct for the management of the disease. Lifelong exposure to altitude is accompanied by a lower risk for obesity, whereas altitude sojourns are generally associated with a loss of body mass. A negative energy balance upon exposure to hypoxia can be due to a combination of changes in determinants of energy expenditure (resting metabolic rate and physical activity energy expenditure) and energy intake (appetite). Over the past 15 years, the potential therapeutic interest of hypobaric or normobaric hypoxic exposure in individuals with obesity—to lower body mass and improve health status—has become an active field of research. Various protocols have been implemented, using actual altitude sojourns or intermittent normobaric hypoxic exposures, at rest or in association with physical activity. Although several studies suggest benefits on body mass and cardiovascular and metabolic variables, further investigations are required before recommending hypoxic exposure in obesity management programs. Future studies should also better clarify the effects of hypoxia on appetite, the intestinal microbiota, and finally on overall energy balance.
... Further, many military personnel experience these severe and unavoidable periods of exercise-and diet-induced energy deficit and associated loss of lean body mass repeatedly over their military career, raising concerns about the potential accumulated health effects of those energy deficits. The US military has sponsored considerable research to develop nutritional countermeasures to mitigate lean body mass loss under these conditions; however, dietary interventions, including those attempting to leverage the anabolic potential of increased protein intake, have been ineffective during severe energy deficit [5][6][7]. ...
... the effects of exogenous testosterone administration on body composition changes during severe energy deficit and recovery (Fig. 2). Phase 1 was a 14-d (days [1][2][3][4][5][6][7][8][9][10][11][12][13][14], free-living, eucaloric diet period. Total daily energy expenditure for diet prescriptions during Phase 1 was determined using the Mifflin St. Jeor Equation with an activity factor of 1.3 to account for activities of daily living, and in combination with results from 7-d accelerometer data and 3-d activity logs collected during screening visits [14]. ...
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Background: Severe energy deficits during military operations, produced by significant increases in exercise and limited dietary intake, result in conditions that degrade lean body mass and lower-body muscle function, which may be mediated by concomitant reductions in circulating testosterone. Methods: We conducted a three-phase, proof-of-concept, single centre, randomised, double-blind, placebo-controlled trial (CinicalTrials.gov, NCT02734238) of non-obese men: 14-d run-in, free-living, eucaloric diet phase; 28-d live-in, 55% exercise- and diet-induced energy deficit phase with (200 mg testosterone enanthate per week, Testosterone, n = 24) or without (Placebo, n = 26) exogenous testosterone; and 14-d recovery, free-living, ad libitum diet phase. Body composition was the primary end point; secondary endpoints included lower-body muscle function and health-related biomarkers. Findings: Following energy deficit, lean body mass increased in Testosterone and remained stable in Placebo, such that lean body mass significantly differed between groups [mean difference between groups (95% CI), 2.5 kg (3.3, 1.6); P < .0001]. Fat mass decreased similarly in both treatment groups [0.2 (-0.4, 0.7), P = 1]. Change in lean body mass was associated with change in total testosterone (r = 0.71, P < .0001). Supplemental testosterone had no effect on lower-body muscle function or health-related biomarkers. Interpretation: Findings suggest that supplemental testosterone may increase lean body mass during short-term severe energy deficit in non-obese, young men, but it does not appear to attenuate lower-body functional decline. Funding: Collaborative Research to Optimize Warfighter Nutrition projects I and II, Joint Program Committee-5, funded by the US Department of Defence.
... Participants were in good health and refrained from consuming alcohol, caffeine, or dietary supplements, and nicotine products during the study. Data presented in this manuscript were collected as part of a larger study examining the impact of high-altitude exposure and underfeeding on skeletal muscle mass, intramuscular regulators of muscle anabolism and proteolysis, and substrate metabolism Margolis et al. 2018;Young et al. 2018). This manuscript reports observations from only the sea-level experiments, in which acute miRNA expression and their targets were measured in response to aerobic exercise, with or without carbohydrate, and recovery protein feeding. ...
... After obtaining informed consent, participants were randomly assigned to consume either a carbohydrate (CHO; n = 9) or flavor-matched non-nutritive control (CON; n = 8) drink during 80 min of steady-state treadmill exercise (Young et al. 2018). Randomization was computer generated, with 1:1 allocation for the parallel groups. ...
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Ingesting protein and carbohydrate together during aerobic exercise suppresses the expression of specific skeletal muscle microRNA and promotes muscle hypertrophy. Determining whether there are independent effects of carbohydrate and protein on microRNA will allow for a clearer understanding of the mechanistic role microRNA serve in regulating skeletal muscle protein synthetic and proteolytic responses to nutrition and exercise. This study determined skeletal muscle microRNA responses to aerobic exercise with or without carbohydrate, and recovery whey protein (WP). Seventeen males were randomized to consume carbohydrate (CHO; 145 g; n = 9) or non‐nutritive control (CON; n = 8) beverages during exercise. Muscle was collected before (BASE) and after 80 min of steady‐state exercise (1.7 ± 0.3 V̇O2 L·min⁻¹) followed by a 2‐mile time trial (17.9 ± 3.5 min; POST), and 3‐h into recovery after consuming WP (25 g; REC). RT‐qPCR was used to determine microRNA and mRNA expression. Bioinformatics analysis was conducted using the mirPath software. Western blotting was used to assess protein signaling. The expression of six microRNA (miR‐19b‐3p, miR‐99a‐5p, miR‐100‐5p, miR‐222‐3p, miR‐324‐3p, and miR‐486‐5p) were higher (P < 0.05) in CHO compared to CON, all of which target the PI3K‐AKT, ubiquitin proteasome, FOXO, and mTORC1 pathways. p‐AKTThr473 and p‐FOXO1Thr24 were higher (P < 0.05) in POST CHO compared to CON. The expression of PTEN was lower (P < 0.05) in REC CHO than CON, while MURF1 was lower (P < 0.05) POST CHO than CON. These findings suggest the mechanism by which microRNA facilitate skeletal muscle adaptations in response to exercise with carbohydrate and protein feeding is by inhibiting markers of proteolysis.
... Weight loss is a common phenomenon at altitude because of hypoxia- induced appetite suppression combined with an increase in basal metabolic rate . Although a daily energy deficit of about 10% may not reduce performance in the short- term as long as glycogen stores are maintained (Kechijan, 2011), severe and prolonged energy restriction at altitude negatively influences muscle mass regardless of protein intake ( Berryman et al., 2018), which can compromise systemic immune function (Gleeson, 2013). Athletes should be informed that their appetite may not accurately reflect their true nutritional needs. ...
... The recommended protein intake for athletes engaged in heavy training at sea level are between 20 and 25 g of high-quality protein consumed after exercise ( Witard et al., 2014), although athletes at altitude will require somewhat more protein. Based on a recent study, consuming a higher-protein diet (2.0 g protein/kg body weight per day) did not protect LBM during severe energy deficit at high altitude ( Berryman et al., 2018). However, caution is warranted to extrapolate results from high to moderate altitude environments. ...
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It was the Summer Olympic Games 1968 held in Mexico City (2,300 m) that required scientists and coaches to cope with the expected decline of performance in endurance athletes and to establish optimal preparation programs for competing at altitude. From that period until now many different recommendations for altitude acclimatization in advance of an altitude competition were proposed, ranging from several hours to several weeks. Those recommendations are mostly based on the separate consideration of the physiology of acclimatization, psychological issues, performance changes, logistical or individual aspects, but there is no review considering all these aspects in their entirety. Therefore, the present work primarily focusses on the period of altitude sojourn prior to the competition at altitude based on physiological and psychological aspects complemented by nutritional and sports practical considerations.
... As previously reported , TBM loss was more than expected for an estimated, prescribed energy deficit of 40%. As such, changes in body energy stores were used to better estimate the total daily energy deficit (Hoyt et al. 2006;Berryman et al. 2018). Those estimates are presented in this paper for descriptive purposes and to explore the role of energy balance on modulating muscle inflammation. ...
... L/min, 506 kcal/30 min) elicits an 8.5 to 12-fold increase in Fn14 gene expression 12-24 h postexercise. In the current study, exercise was prohibited for at least 36 h prior to the muscle biopsy, but on the other days at HA participants were required to complete multiple bouts (Bamman et al. 2015;Burd and De Lisio 2017;Berryman et al. 2018) of aerobic-type exercise to elicit an EIEE of approximately 670 kcal/day. The observed increase in Fn14 and associated myogenic regulatory factors following 21 day of energy deficit at HA was likely a residual and/or cumulative response to repeated exercise bouts performed at least 36 h before muscle samples were collected. ...
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Intramuscular factors that modulate fat-free mass (FFM) loss in lowlanders exposed to energy deficit during high-altitude (HA) sojourns remain unclear. Muscle inflammation may contribute to FFM loss at HA by inducing atrophy and inhibiting myogenesis via the tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible protein 14 (Fn14). To explore whether muscle inflammation modulates FFM loss reportedly developing during HA sojourns, muscle inflammation, myogenesis, and proteolysis were assessed in 16 men at sea level (SL) and following 21 days of energy deficit (-1862 ± 525 kcal/days) at high altitude (HA, 4300 m). Total body mass (TBM), FFM, and fat mass (FM) were assessed using DEXA. Gene expression and proteolytic enzymatic activities were assessed in muscle samples collected at rest at SL and HA. Participants lost 7.2 ± 1.8 kg TBM (P < 0.05); 43 ± 30% and 57 ± 30% of the TBM lost was FFM and FM, respectively. Fn14, TWEAK, TNF alpha-receptor (TNFα-R), TNFα, MYOGENIN, and paired box protein-7 (PAX7) were upregulated (P < 0.05) at HA compared to SL. Stepwise linear regression identified that Fn14 explained the highest percentage of variance in FFM loss (r2 = 0.511, P < 0.05). Dichotomization of volunteers into HIGH and LOW Fn14 gene expression indicated HIGH lost less FFM and more FM (28 ± 28% and 72 ± 28%, respectively) as a proportion of TBM loss than LOW (58 ± 26% and 42 ± 26%; P < 0.05) at HA. MYOGENIN gene expression was also greater for HIGH versus LOW (P < 0.05). These data suggest that heightened Fn14 gene expression is not catabolic and may protect FFM during HA sojourns.
... Prolonged negative protein balance and concomitant muscle loss may compromise physical performance and increase injury risk and lost duty time, which further diminishes warfighter readiness [12,74]. While additional protein intake is effective in mitigating compromises in body protein homeostasis, especially when combined with resistance exercise [75], as the caloric deficit increases (~40% [73,75,76]) the anabolic effects of protein are absent, and the constituent essential amino acids (EAA) are prioritized as carbon skeletons for energy production. ...
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This position stand aims to provide an evidence-based summary of the energy and nutritional demands of tactical athletes to promote optimal health and performance while keeping in mind the unique challenges faced due to work schedules, job demands, and austere environments. After a critical analysis of the literature, the following nutritional guidelines represent the position of the International Society of Sports Nutrition (ISSN). GENERAL RECOMMENDATIONS Nutritional considerations should include the provision and timing of adequate calories, macronutrients, and fluid to meet daily needs as well as strategic nutritional supplementation to improve physical, cognitive, and occupational performance outcomes; reduce risk of injury, obesity, and cardiometabolic disease; reduce the potential for a fatal mistake; and promote occupational readiness. MILITARY RECOMMENDATIONS Energy demands should be met by utilizing the Military Dietary Reference Intakes (MDRIs) established and codified in Army Regulation 40-25. Although research is somewhat limited, military personnel may also benefit from caffeine, creatine monohydrate, essential amino acids, protein, omega-3-fatty acids, beta-alanine, and L-tyrosine supplementation, especially during high-stress conditions. FIRST RESPONDER RECOMMENDATIONS Specific energy needs are unknown and may vary depending on occupation-specific tasks. It is likely the general caloric intake and macronutrient guidelines for recreational athletes or the Acceptable Macronutrient Distribution Ranges for the general healthy adult population may benefit first responders. Strategies such as implementing wellness policies, setting up supportive food environments, encouraging healthier food systems, and using community resources to offer evidence-based nutrition classes are inexpensive and potentially meaningful ways to improve physical activity and diet habits. The following provides a more detailed overview of the literature and recommendations for these populations.
... For example, doubling protein intake from the recommended daily allowance of 0.8 g·kg·day −1 to 1.6 g·kg·day −1 resulted in reduced lean mass loss in a group of healthy young men who were in energy deficit, but tripling protein intake had no further benefits (Pasiakos et al., 2013). It seems that the capacity of protein to mitigate skeletal muscle trade-offs when energy is scarce may also depend on the extent of deficit, with more severe deficits leading to increased protein oxidation over the protection of muscle mass (Berryman et al., 2018). This is consistent with a life history perspective, in that the more energy resources are constrained, the more inflexible energy allocation becomes; in other words, greater deficits in energy availability relative to the body's requirements will necessitate more severe trade-offs. ...
Article
Energy is a finite resource that is competitively distributed among the body’s systems and biological processes. During times of scarcity, energetic “trade-offs” may arise if less energy is available than is required to optimally sustain all systems. More immediately essential functions are predicted to be prioritized, even if this necessitates the diversion of energy away from – and potential downregulation of – others. These concepts are encompassed within life history theory, an evolutionary framework with considerable potential to enhance understanding of the evolved biological response to periods of energy deficiency. Skeletal muscle is a particularly interesting tissue to investigate from this perspective, given that it is one of the largest and most energetically costly tissues within the body. It is also highly plastic, responsive to a broad range of stimuli, and contributes to many essential bodily functions, e.g., mechanical, regulatory and storage. These functions may be traded off against each other during periods of energy deficiency, with the nature of the trade-off’s dependent on the characteristics of the individual and the circumstances within which the deficit occurs. In this review, we consider the skeletal muscle response to periods of energy deficiency from a life history perspective, along with how this response may be influenced by factors including sex, age, body composition, training and nutritional status.
... Meta-analyses data suggests that the performance of elite endurance athletes can improve by ~4-5% following methods of live high-train low and live high-train high altitude training [3]. However, some athletes may not respond favourably to such practices potentially due to the negative physiological consequences of training in a hypoxic environment (e.g., impaired sleep quality, weight loss, decrease in muscle protein synthesis) [4,5]. ...
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Altitude training increases haemoglobin, erythropoietin values among athletes, but may have negative physiological consequences. An alternative, although less explored, that has the potential to positively influence performance while avoiding some of the negative physiological consequences of hypoxia is sand training. Ten endurance-trained athletes (age: 20.8 ± 1.4, body mass: 57.7 ± 8.2 kg, stature: 176 ± 6 cm; 5000 m 14:55.00 ±0:30 min) performed three 21-day training camps at different locations: at a high altitude (HIGH), at the sea-level (CTRL), at the sea-level on the sand (SAND). Differences in erythropoietin (EPO) and haemoglobin (Hb) concentration, body weight, VO2max and maximal aerobic velocity (VMA) before and after each training cycle were compared. Data analysis has indicated that training during HIGH elicited a greater increase in VO2max (2.4 ± 0.2%; p = 0.005 and 1.0 ± 0.2%; p < 0.001) and VMA (2.4 ± 0.2%, p < 0.001 and 1.2 ± 0.2%; p = 0.001) compared with CTRL and SAND. While increases in VO2max and VMA following SAND were greater (1.3 ± 0.1%; p < 0.001 and 1.2 ± 0.1%; p < 0.001) than those observed after CTRL. Moreover, EPO increased to a greater extent following HIGH (25.3 ± 2.7%) compared with SAND (11.7 ± 1.6%, p = 0.008) and CTRL (0.1 ± 0.3%, p < 0.001) with a greater increase (p < 0.01) following SAND compared with CTRL. Furthermore, HIGH and SAND elicited a greater increase (4.9 ± 0.9%; p = 0.001 and 3.3 ± 1.1%; p = 0.035) in Hb compared with CTRL. There was no difference in Hb changes observed between HIGH and SAND (p = 1.0). Finally, athletes lost 2.1 ± 0.4% (p = 0.001) more weight following HIGH vs. CTRL, while there were no differences in weight changes between HIGH vs. SAND (p = 0.742) and SAND vs. CTRL (p = 0.719). High-altitude training and sea-level training on sand resulted in significant improvements in EPO, Hb, VMA, and VO2max that exceeded changes in such parameters following traditional sea-level training. While high-altitude training elicited greater relative increases in EPO, VMA, and VO2max, sand training resulted in comparable increases in Hb and may prevent hypoxia-induced weight loss. Citation: Man, M.C.; Ganera, C.; Bărbule, G.D.; Krzysztofik, M.; Panaet, A.E.; Cucui, A.I.; Tohănean, I.; Alexe, D.I. The Modifications of Haemoglobin, Erythropoietin Values and Running Performance While Training at Mountain vs. Hilltop vs. Seaside. Int. J. Environ. Res. Public Health 2021, 18, 9486. https://
... To reduce total body mass, athletes may restrict energy intake, resulting in a negative energy balance (e.g., energy expenditure > energy intake) [4,5]. However, periods of negative energy balance also typically reduce FFM, and that loss of FFM during energy deficit can account for as much as~50% of total mass lost in lean individuals [6][7][8]. Reductions in FFM during negative energy balance may impair physical performance [9]. ...
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Background To achieve ideal strength/power to mass ratio, athletes may attempt to lower body mass through reductions in fat mass (FM), while maintaining or increasing fat-free mass (FFM) by manipulating their training regimens and diets. Emerging evidence suggests that consumption of high-fat, ketogenic diets (KD) may be advantageous for reducing body mass and FM, while retaining FFM. Methods A systematic review of the literature was conducted using PubMed and Cochrane Library databases to compare the effects of KD versus control diets (CON) on body mass and composition in physically active populations. Randomized and non-randomized studies were included if participants were healthy (free of chronic disease), physically active men or women age ≥ 18 years consuming KD (< 50 g carbohydrate/d or serum or whole blood β-hydroxybutyrate (βhb) > 0.5 mmol/L) for ≥14 days. Results Thirteen studies (9 parallel and 4 crossover/longitudinal) that met the inclusion criteria were identified. Aggregated results from the 13 identified studies show body mass decreased 2.7 kg in KD and increased 0.3 kg in CON. FM decreased by 2.3 kg in KD and 0.3 kg in CON. FFM decreased by 0.3 kg in KD and increased 0.7 kg in CON. Estimated energy balance based on changes in body composition was − 339 kcal/d in KD and 5 kcal/d in CON. Risk of bias identified some concern of bias primarily due to studies which allowed participants to self-select diet intervention groups, as well as inability to blind participants to the study intervention, and/or longitudinal study design. Conclusion KD can promote mobilization of fat stores to reduce FM while retaining FFM. However, there is variance in results of FFM across studies and some risk-of-bias in the current literature that is discussed in this systematic review.
... Reductions in concentrations of these metabolites have also been reported with decreased dietary protein intake (53), which results in negative protein balance. Taken together, these findings suggest that increased reliance on amino acids for oxidative purposes may, in part, help explain declines in mechanistic target of rapamycin complex 1 anabolic signaling (54), negative net protein balance (55,56), and reductions in muscle mass (55-57) that occur in unacclimatized lowlanders sojourning at HA. ...
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Article
Hypoxia-induced insulin resistance appears to suppress exogenous glucose oxidation during metabolically-matched aerobic exercise during acute (<8-h) high-altitude (HA) exposure. However, a better understanding of this metabolic dysregulation is needed to identify interventions to mitigate these effects. The objective of this study was to determine if differences in metabolomic profiles during exercise at sea level (SL) and HA are reflective of hypoxia-induced insulin resistance. Native lowlanders (n=8 males) consumed 145g (1.8g/min) of glucose while performing 80-min of metabolically-matched treadmill exercise at SL (757 mmHg) and HA (460 mmHg) after 5-h exposure. Exogenous glucose oxidation and glucose turnover were determined using indirect calorimetry and dual tracer technique (13C-glucose and [6,6-2H2]-glucose). Metabolite profiles were analyzed in serum as change (Δ), calculated by subtracting postprandial/exercised state SL (ΔSL) and HA (ΔHA) from fasted, rested conditions at SL. Compared to SL, exogenous glucose oxidation, glucose rate of disappearance , and glucose metabolic clearance rate (MCR) were lower (P<0.05) during exercise at HA. 118 metabolites differed between ΔSL and ΔHA (P<0.05, Q<0.10). Differences in metabolites indicated increased glycolysis, TCA cycle, amino acid catabolism, oxidative stress, and fatty acid storage, and decreased fatty acid mobilization for ΔHA. BCAA and oxidative stress metabolites, Δ3-methyl-2-oxobutyrate (r=-0.738) and Δgamma-glutamylalanine (r=-0.810), were inversely associated (P<0.05) with Δexogenous glucose oxidation. Δ3-hydroxyisobutyrate (r=-0.762) and Δ2-hydroxybutyrate/2-hydroxyisobutyrate (r=-0.738) were inversely associated (P<0.05) with glucose MCR. Coupling global metabolomics and glucose kinetic data suggest that the underlying cause for diminished exogenous glucose oxidative capacity during aerobic exercise is acute hypoxia-mediated peripheral insulin resistance.
... Here our emphasis will be placed on the applications of stable isotope tracer methodology owing mainly to (1) safety issues, particularly for humans and (2) the versatility of stable isotope tracers in assessing various aspects of metabolism [7,15,16,[29][30][31][32][33][34][35]. In addition, assessments of metabolic flux using stable isotope tracer methodology are typically accomplished in conjunction with the use of gas or liquid chromatography mass spectrometry (GC-or LC-MS) [36,37] or magnetic resonance spectroscopy [38,39] with essentially the same purpose: i.e., determining tracer enrichment (e.g., magnitude of labeling, expressed as various ways) [15,16], which will be briefly discussed below. ...
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Like other substrates, plasma glucose is in a dynamic state of constant turnover (i.e., rates of glucose appearance [Ra glucose] into and disappearance [Rd glucose] from the plasma) while staying within a narrow range of normal concentrations, a physiological priority. Persistent imbalance of glucose turnover leads to elevations (i.e., hyperglycemia, Ra>Rd) or falls (i.e., hypoglycemia, Ra<Rd) in the pool size, leading to clinical conditions such as diabetes. Endogenous Ra glucose is divided into hepatic glucose production via glycogenolysis and gluconeogenesis (GNG) and renal GNG. On the other hand, Rd glucose, the summed rate of glucose uptake by tissues/organs, involves various intracellular metabolic pathways including glycolysis, the tricarboxylic acid (TCA) cycle, and oxidation at varying rates depending on the metabolic status. Despite the dynamic nature of glucose metabolism, metabolic studies typically rely on measurements of static, snapshot information such as the abundance of mRNAs and proteins and (in)activation of implicated signaling networks without determining actual flux rates. In this review, we will discuss the importance of obtaining kinetic information, basic principles of stable isotope tracer methodology, calculations of in vivo glucose kinetics, and assessments of metabolic flux in experimental models in vivo and in vitro.
... Several factors contribute to energy deficit-induced lean mass loss, including downregulated MPS [16][17][18], blunted MPS-associated anabolic signaling responses to feeding [14], and increased whole-body protein oxidation [19][20][21]. The downregulation of postabsorptive and postprandial MPS is further exacerbated during severe energy deficit because dietary protein is used as a readily available, oxidizable energy source to meet increased whole-body energy demands [14,22]. While recommendations based on MPS responses provide valuable guidance for prioritizing muscle mass accretion and maintenance in healthy individuals during energy balance, they may overlook the potential benefit of protein intake on whole-body protein balance (whole-body protein synthesis-whole-body protein breakdown) during energy deficit. ...
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Protein intake recommendations to optimally stimulate muscle protein synthesis (MPS) are derived from dose-response studies examining the stimulatory effects of isolated intact proteins (e.g., whey, egg) on MPS in healthy individuals during energy balance. Those recommendations may not be adequate during periods of physiological stress, specifically the catabolic stress induced by energy deficit. Providing supplemental intact protein (20–25 g whey protein, 0.25–0.3 g protein/kg per meal) during strenuous military operations that elicit severe energy deficit does not stimulate MPS-associated anabolic signaling or attenuate lean mass loss. This occurs likely because a greater proportion of the dietary amino acids consumed are targeted for energy-yielding pathways, whole-body protein synthesis, and other whole-body essential amino acid (EAA)-requiring processes than the proportion targeted for MPS. Protein feeding formats that provide sufficient energy to offset whole-body energy and protein-requiring demands during energy deficit and leverage EAA content, digestion, and absorption kinetics may optimize MPS under these conditions. Understanding the effects of protein feeding format-driven alterations in EAA availability and subsequent changes in MPS and whole-body protein turnover is required to design feeding strategies that mitigate the catabolic effects of energy deficit. In this manuscript, we review the effects, advantages, disadvantages, and knowledge gaps pertaining to supplemental free-form EAA, intact protein, and protein-containing mixed meal ingestion on MPS. We discuss the fundamental role of whole-body protein balance and highlight the importance of comprehensively assessing whole-body and muscle protein kinetics when evaluating the anabolic potential of varying protein feeding formats during energy deficit.
... Whole-body protein synthesis (PS) may reach a maximum 54 6 in response to increasing amounts of EAA. However, whole-body net protein balance (NET; PS 55 -whole-body protein breakdown, PB) may increase further if the rise in EAA concentrations 56 subsequent to increasing EAA intake induce a reduction in PB [14]. This aspect of protein status 57 in response to energy deficit and EAA intake is only evident when whole-body protein turnover 58 is measured in addition to MPS. ...
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Background & aims Consuming 0.10-0.14 g essential amino acids (EAA)/kg/dose (0.25-0.30 g protein/kg/dose) maximally stimulates muscle protein synthesis (MPS) during energy balance. Whether consuming EAA beyond that amount enhances MPS and whole-body anabolism following energy deficit is unknown. The aims of this study were to determine the effects of standard and high EAA ingestion on mixed MPS and whole-body protein turnover following energy deficit. Design Nineteen males (mean±SD; 23 ± 5 y; 25.4 ± 2.7 kg/m²) completed a randomized, double-blind crossover study consisting of two, 5-d energy deficits (-30 ± 4 % of total energy requirements), separated by 14-d. Following each energy deficit, mixed MPS and whole-body protein synthesis (PS), breakdown (PB), and net balance (NET) were determined at rest and post-resistance exercise (RE) using primed, constant L-[²H5]-phenylalanine and L-[²H2]-tyrosine infusions. Beverages providing standard (0.1 g/kg, 7.87 ± 0.87 g) or high (0.3 g/kg, 23.5 ± 2.54 g) EAA were consumed post-RE. Circulating EAA were measured. Results Postabsorptive mixed MPS (%/h) at rest was not different (P = 0.67) between treatments. Independent of EAA, postprandial mixed MPS at rest (standard EAA, 0.055 ± 0.01; high EAA, 0.061 ± 0.02) and post-RE (standard EAA, 0.055 ± 0.01; high EAA, 0.065 ± 0.02) were greater than postabsorptive mixed MPS at rest (P = 0.02 and P = 0.01, respectively). Change in (Δ postabsorptive) whole-body (g/180min) PS and PB was greater for high than standard EAA [mean treatment difference (95%CI), 3.4 (2.3,4.4); P = 0.001 and -15.6 (-17.8,-13.5); P = 0.001, respectively]. NET was more positive for high than standard EAA [19.0 (17.3, 20.7); P = 0.001]. EAA concentrations were greater in high than standard EAA (P = 0.001). Conclusions These data demonstrate that high compared to standard EAA ingestion enhance whole-body protein status during underfeeding. However, the effects of consuming high and standard EAA on mixed MPS are the same during energy deficit. Clinical Trial Registry NCT03372928, https://clinicaltrials.gov.
... Although there was no phase-by-treatment interaction, post hoc pairwise comparisons revealed that the main effect of treatment was likely driven by greater muscle mass in TEST compared with PLA at Recovery and EOS. A lack of change in muscle mass during the energy deficit may be attributed to the body's use of dietary protein to support energy production rather than MPS, which can occur with more severe energy deficits (42). In contrast, the proteome-wide stimulus derived from testosterone resulted in muscle accretion once energy and dietary essential amino acids were readily available during recovery. ...
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Objectives Short-term energy deficit reduces acute measures of mixed muscle protein synthesis (MPS) and suppresses the hypothalamic-pituitary axis and endogenous testosterone synthesis. We hypothesized that testosterone supplementation could mitigate the effects of energy deficit on MPS. We conducted a randomized, double-blind, placebo-controlled trial to determine the effects of 28 days of tightly-controlled severe energy deficit (deficit 55% of total energy requirements) on measures of mixed-MPS and proteome-wide protein dynamics in non-obese men either given 200 mg testosterone enanthate (Testosterone, n = 24) or placebo (Placebo, n = 26) injections per week. Methods Participants received daily aliquots of deuterated water (2H2O) for 42 consecutive days (14-d weight maintenance period followed by 28-d energy deficit). Muscle biopsies were collected at rest in a fasted state at the end of the weight maintenance phase (PRE) and at the middle (MID) and end (POST) of the 28-d energy deficit. Mixed-MPS and proteome-wide protein fractional synthesis rates (FSR) were quantified. Changes over time and differences between Testosterone and Placebo were determined for mixed-MPS, and cross-sectional comparisons between Testosterone and Placebo were performed at MID and POST for proteome dynamics. Results In both Testosterone and Placebo, mixed-MPS were 40% and 33% lower (P < 0.0005) at MID and POST energy deficit, respectively, compared to PRE, with no differences between groups or between MID and POST. Proteome-wide FSR of individual muscle proteins did not differ between Testosterone and Placebo at any time point. However, at POST, the number of individual proteins with higher FSR in Testosterone than Placebo was significant by 2-tailed binomial test (P < 0.05), with values ranging from 20–32% higher FSR for myofibrillar, mitochondrial and cytosolic proteins. Conclusions Findings confirm the pronounced effect of short-term severe energy deficit on mixed-MPS and suggest the anabolic suppression occurs largely independent of testosterone. However, proteome-wide protein dynamics may reveal a novel time sensitive signal by which supplemental testosterone triggers a delayed increase in MPS, providing a synthetic mechanism for muscle mass preservation or accrual. Funding Sources Supported by DHP JPC-5/MOMRP; authors’ views not official U.S. Army or DoD policy.
... However, the efficacy of T administration in healthy populations exposed to severe catabolic stress for short durations highlights a need to close this knowledge gap. In particular, special operations forces combat training results in a hypogonadal state [11,28,29], a loss of lean mass [10,11,30], and decreased performance outcomes due to a convergence of many different physiological and environmental stressors [29,[31][32][33][34]. Thus, the ability to discern the short-term anabolic potential of T may be of substantial benefit to certain military populations whose occupational demands often include exposure to extreme catabolic stress. ...
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We previously demonstrated that improved net muscle protein balance, via enhanced protein synthetic efficiency, occurs 5 days after testosterone (T) administration. Whether the effects of T on muscle protein kinetics occur immediately upon exposure is not known. We investigated the effects of acute T exposure on leg muscle protein kinetics and selected amino acid (AA) transport using the arteriovenous balance model, and direct calculations of mixed-muscle protein fractional synthesis (FSR) and breakdown (FBR) rates. Four healthy men were studied over a 5 h period with and without T (infusion rate, 0.25 mg·min- 1). Muscle protein FSR, FBR, and net protein balance (direct measures and model derived) were not affected by T, despite a significant increases in arterial (p = 0.009) and venous (p = 0.064) free T area under the curve during T infusion. T infusion had minimal effects on AA transport kinetics, affecting only the outward transport and total intracellular rate of appearance of leucine. These data indicate that exposing skeletal muscle to T does not confer immediate effects on AA kinetics or muscle anabolism. There remains an uncertainty as to the earliest discernable effects of T on skeletal muscle protein kinetics after initial administration.
... Consuming higher amounts of protein during typical moderate energy-deficient weight loss diets (i.e., 500-750 kcal/d deficit [25]) preserves muscle mass in an otherwise catabolic physiological environment [6]. However, the protective effect of higher-protein diets on muscle and whole-body protein homeostasis is compromised as the severity of energy deficit increases beyond 40% of daily energy needs, as a greater proportion of dietary amino acids are oxidized for energy production, thereby minimizing amino acid availability to support protein balance [26] (Figure 1). However, most adults rarely experience acute or sustained periods of severe energy deficit, except for perhaps acute fasting for religious reasons, poorly-constructed drastic weight loss plans, preparation and/or recovery from bariatric surgery, or scenarios where food availability is severely limited (e.g., victims of natural disasters, emergency responders, etc.). ...
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Adequate consumption of dietary protein is critical for the maintenance of optimal health during normal growth and aging. The current Recommended Dietary Allowance (RDA) for protein is defined as the minimum amount required to prevent lean body mass loss, but is often misrepresented and misinterpreted as a recommended optimal intake. Over the past two decades, the potential muscle-related benefits achieved by consuming higher-protein diets have become increasingly clear. Despite greater awareness of how higher-protein diets might be advantageous for muscle mass, actual dietary patterns, particularly as they pertain to protein, have remained relatively unchanged in American adults. This lack of change may, in part, result from confusion over the purported detrimental effects of higher-protein diets. This manuscript will highlight common perceptions and benefits of dietary protein on muscle mass, address misperceptions related to higher-protein diets, and comment on the translation of academic advances to real-life application and health benefit. Given the vast research evidence supporting the positive effects of dietary protein intake on optimal health, we encourage critical evaluation of current protein intake recommendations and responsible representation and application of the RDA as a minimum protein requirement rather than one determined to optimally meet the needs of the population.
... Design expertise for the initial questionnaire was provided by the US Army Research Institute of Environmental Medicine, the Department of Defense research institution responsible for conducting research on the nutritional status of military personnel. This institution is staffed by doctoral and masters-level nutrition experts, including dietitians who routinely assess the dietary requirements, habits, and behaviors of diverse military populations as well as civilians, including college students and emergency workers (3,(26)(27)(28). To date, surveys conducted by the US Army Research Institute of Environmental Medicine, typically in collaboration with other institutions with expertise in the populations of interest, have evaluated dietary supplement use in >7000 military personnel on bases in the United States and abroad, as well as >1000 college students from 5 geographically dispersed US universities and the results have been published in various peer-reviewed journals (2,3,7,8,(10)(11)(12). ...
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Substantial data on the use of dietary supplements by the general adult population are available, but many population subgroups have not been extensively studied. Because military service members and young people consume large amounts of dietary supplements, including for enhancement of physical performance, weight control, and bodybuilding, which can be dangerous, we developed a comprehensive questionnaire to characterize patterns of supplement use in these and other populations. The questionnaire has been used to study >7000 military service members and 1000 college students. This supplement article presents a detailed description of the questionnaire, which contains comprehensive questions on demographic characteristics, exercise habits, attitudes with regard to dietary supplements, and amount of money spent on supplements. Intakes of specific dietary supplements and caffeine, frequency of use, and reasons for use are assessed. The questionnaire was designed for studying dietary supplement and caffeine intake patterns with the use of paper-and-pencil administration to military populations and was modified for use with college students and for computer and Web administration. It is available online at https://go.usa.gov/xn9FP and in the Supplemental File for this publication. It can be used to study other populations if minor modifications are made. The online version of the questionnairewill be updated periodically as newversions become available. In conclusion, a validated, detailed, noncopyrighted questionnaire designed to assess the use of dietary supplements, energy drinks (and related products), and caffeine is available for use in diverse populations. The format of the questionnaire is adaptable to computer administration and scoring, and it can be customized for specific subpopulations, locations, and product categories including updates that reflect changes in the availability of supplements or availability of new products.
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We have recently reported that hypobaric hypoxia (HH) reduces plasma volume (PV) in men by decreasing total circulating plasma protein (TCPP). Here, we investigated whether this applies to women and whether an inflammatory response and/or endothelial glycocalyx shedding could facilitate the TCCP reduction. We further investigated whether acute HH induces a short-lived diuretic response that was overlooked in our recent study, where only 24-h urine volumes were evaluated. In a strictly controlled crossover protocol, twelve women underwent two 4-day sojourns in a hypobaric chamber: one in normoxia (NX) and one in HH equivalent to 3,500m altitude. PV, urine output, TCPP, and markers for inflammation and glycocalyx shedding were measured repeatedly. Total body water (TBW) was determined pre- and post-sojourns by deuterium dilution. PV was reduced after 12h of HH and thereafter remained 230-330ml lower than in NX (p<0.0001). Urine flow was 45% higher in HH than in NX throughout the first 6h (p=0.01), but lower during the second half of the first day (p<0.001). 24-h urine volumes (p≥0.37) and TBW (p≥0.14) were not different between the sojourns. TCPP was lower in HH than in NX at the same time points as PV (p<0.001) but inflammatory or glycocalyx shedding markers were not consistently increased. As in men, and despite initially increased diuresis, HH-induced PV contraction in women is driven by a loss of TCPP and ensuing fluid redistribution, rather than by fluid loss. The mechanism underlying the TCPP reduction remains unclear but does not seem to involve inflammation or glycocalyx shedding.
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Human Molecular and Physiological Responses to Hypoxia Towards the end of the 19th century, the French physician Denis Jourdan was the first to understand and state the critical role of the reduction of oxygen at altitude, which he defined as anoxemia. This term indicated the diminished quantity of oxygen contained in the blood of people living at high altitude, where the tension of the oxygen in the surrounding air is considerably decreased (West and Richalet, 2013). In the following 150 years, studies on hypoxia took off, ranging from purely clinical and functional aspects to cellular and biomolecular ones, from acute to chronic hypoxia and analyzing not only the altitude-hypoxia but also the hypoxia related to underlying diseases. Currently, the study of pathophysiological responses at altitude is a model to investigate the mechanisms of response to hypoxia in any condition, also in critical illnesses (Grocott et al., 2007). In this special issue, a series of ten articles with different approaches applied to the study of molecular and physiological responses to hypoxia were collected.
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Context Effects of testosterone on integrated muscle protein metabolism and muscle mass during energy deficit are undetermined. Objective The objective was to determine the effects of testosterone on mixed-muscle protein synthesis (MPS), proteome-wide fractional synthesis rates (FSR), and skeletal muscle mass during energy deficit. Design This was a randomized, double-blind, placebo-controlled trial (ClinicalTrials.gov, NCT02734238). Setting The study was conducted at Pennington Biomedical Research Center. Participants Fifty healthy men. Intervention The study consisted of 14 days of weight maintenance, followed by a 28-day 55% energy deficit with 200 mg testosterone enanthate (TEST, n=24) or placebo (PLA, n=26) weekly, and up to 42 days of ad libitum recovery feeding. Main Outcome Measures Mixed-MPS and proteome-wide FSR before (Pre), during (Mid) and after (Post) the energy deficit were determined using heavy water (days 1-42) and muscle biopsies. Muscle mass was determined using the D3-Creatine dilution method. Results Mixed-MPS was lower than Pre at Mid and Post (P<0.0005), with no difference between TEST and PLA. The proportion of individual proteins with numerically higher FSR in TEST than PLA was significant by two-tailed binomial test at Post (52/67; P<0.05), but not Mid (32/67; P>0.05). Muscle mass was unchanged during energy deficit, but was greater in TEST than PLA during recovery (P<0.05). Conclusions The high proportion of individual proteins with greater FSR in TEST than PLA at Post suggests exogenous testosterone exerted a delayed but broad stimulatory effect on synthesis rates across the muscle proteome during energy deficit, resulting in muscle mass accretion during subsequent recovery.
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Individuals sojourning at high altitude (≥2,500m) often develop acute mountain sickness (AMS). However, substantial unexplained inter-individual variability in AMS severity exists. Untargeted metabolomics assays are increasingly used to identify novel biomarkers of susceptibility to illness, and to elucidate biological pathways linking environmental exposures to health outcomes. This study used untargeted nuclear magnetic resonance (NMR)-based metabolomics to identify urine metabolites associated with AMS severity during high altitude sojourn. Following a 21-day stay at sea level (SL; 55m), 17 healthy males were transported to high altitude (HA; 4,300m) for a 22-day sojourn. AMS symptoms measured twice daily during the first 5days at HA were used to dichotomize participants according to AMS severity: moderate/severe AMS (AMS; n =11) or no/mild AMS (NoAMS; n =6). Urine samples collected on SL day 12 and HA days 1 and 18 were analyzed using proton NMR tools and the data were subjected to multivariate analyses. The SL urinary metabolite profiles were significantly different ( p ≤0.05) between AMS vs. NoAMS individuals prior to high altitude exposure. Differentially expressed metabolites included elevated levels of creatine and acetylcarnitine, and decreased levels of hypoxanthine and taurine in the AMS vs. NoAMS group. In addition, the levels of two amino acid derivatives (4-hydroxyphenylpyruvate and N-methylhistidine) and two unidentified metabolites (doublet peaks at 3.33ppm and a singlet at 8.20ppm) were significantly different between groups at SL. By HA day 18, the differences in urinary metabolites between AMS and NoAMS participants had largely resolved. Pathway analysis of these differentially expressed metabolites indicated that they directly or indirectly play a role in energy metabolism. These observations suggest that alterations in energy metabolism before high altitude exposure may contribute to AMS susceptibility at altitude. If validated in larger cohorts, these markers could inform development of a non-invasive assay to screen individuals for AMS susceptibility prior to high altitude sojourn.
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Nutrition in sports and human performance incorporates knowledge of the intersection of human physiology and nutrition. Registered dietitian nutritionist (RDN) practitioners in sports and human performance focus on nutrition care that is specific to the individual and their sport/occupational requirements. The Dietitians in Sports, Cardiovascular and Wellness Dietetic Practice Group, along with the Academy of Nutrition and Dietetics Quality Management Committee, have updated the Standards of Practice (SOP) and Standards of Professional Performance (SOPP) for RDNs working in sports and human performance. The SOP and SOPP for RDNs in Sports and Human Performance Nutrition provide indicators that describe three levels of practice: competent, proficient, and expert. The SOP uses the Nutrition Care Process and clinical workflow elements for delivering care to athletic/professional populations. The SOPP describes the following six domains that focus on professional performance: Quality in Practice, Competence and Accountability, Provision of Services, Application of Research, Communication and Application of Knowledge, and Utilization and Management of Resources. Specific indicators outlined in the SOP and SOPP depict how these standards apply to practice. The SOP and SOPP are complementary resources for RDNs and are intended to be used as a self-evaluation tool for assuring competent practice in sports and human performance and for determining potential education and training needs for advancement to a higher practice level in a variety of settings.
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Background Effects of high protein (HP) diets and prolonged energy restriction (ER) on integrated muscle protein kinetics have not been determined. Objective The objective of this study was to measure protein kinetics in response to prolonged ER and HP on muscle protein synthesis (MPS; absolute rates of synthesis) and muscle protein breakdown (MPB; half-lives) for proteins across the muscle proteome. Methods Female 6-wk-old obese Zucker rats (Leprfa+/fa+, n = 48) were randomly assigned to one of four diets for 10 wk: ad libitum-standard protein (AL-SP; 15% kcal from protein), AL-HP (35% kcal from protein), ER-SP, and ER-HP (both fed 60% feed consumed by AL-SP). During week 10, heavy/deuterated water (2H2O) was administered by intraperitoneal injection, and isotopic steady-state was maintained via 2H2O in drinking water. Rats were euthanized after 1 wk, and mixed-MPS as well as fractional replacement rate (FRR), relative concentrations, and half-lives of individual muscle proteins were quantified in the gastrocnemius. Data were analyzed using 2-factor (energy × protein) ANOVAs and 2-tailed t-tests or binomial tests as appropriate. Results Absolute MPS was lower in ER than AL for mixed-MPS (–29.6%; P < 0.001) and MPS of most proteins measured [23/26 myofibrillar, 48/60 cytoplasmic, and 46/60 mitochondrial (P < 0.05)], corresponding with lower gastrocnemius mass in ER compared with AL (–29.4%; P < 0.001). Although mixed-muscle protein half-life was not different between groups, prolonged half-lives were observed for most individual proteins in HP compared with SP in ER and AL (P < 0.001), corresponding with greater gastrocnemius mass in HP than SP (+5.3%; P = 0.043). Conclusions ER decreased absolute bulk MPS and most individual MPS rates compared with AL, and HP prolonged half-lives of most proteins across the proteome. These data suggest that HP, independent of energy intake, may reduce MPB, and reductions in MPS may contribute to lower gastrocnemius mass during ER by reducing protein deposition in obese female Zucker rats.
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The importance of diet and nutrition to military readiness and performance has been recognized for centuries as dietary nutrients sustain health, protect against illness, and promote resilience, performance and recovery. Contemporary military nutrition research is increasingly inter-disciplinary with emphasis often placed on the broad topics of: 1) determining operational nutrition requirements in all environments, 2) characterizing nutritional practices of military personnel relative to the required (role/environment) standards, and 3) developing strategies for improving nutrient delivery and individual choices. This review discusses contemporary issues shared internationally by military nutrition research programs, and highlights emerging topics likely to influence future military nutrition research and policy. Contemporary issues include improving the diet quality of military personnel, optimizing operational rations, and increasing understanding of biological factors influencing nutrient requirements. Emerging areas include the burgeoning field of precision nutrition and its technological enablers.
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Protein turnover reflects the continual synthesis and breakdown of body proteins, and can be measured at a whole-body (i.e. aggregated across all body proteins) or tissue (e.g. skeletal muscle only) level using stable isotope methods. Evaluating protein turnover in free-living environments, such as military training, can help inform protein requirements. We undertook a narrative review of published literature with the aim of reviewing the suitability of, and advancements in, stable isotope methods for measuring protein turnover in field research. The 2 primary approaches for measuring protein turnover are based on precursor-and end-product methods. The precursor method is the gold-standard for measuring acute (over several hours) skeletal muscle protein turnover, whereas the end-product method measures chronic (over several weeks) skeletal muscle protein turnover and provides the opportunity to monitor free-living activities. Both methods require invasive procedures such as the infusion of amino acid tracers and muscle biopsies to assess the uptake of the tracer into tissue. However, the end-product method can also be used to measure acute (over 9-24 h) whole-body protein turnover noninvasively by ingesting 15 N-glycine, or equivalent isotope tracers, and collecting urine samples. The end-product method using 15 N-glycine is a practical method for measuring whole-body protein turnover in the field over short (24 h) time frames and has been used effectively in recent military field research. Application of this method may improve our understanding of protein kinetics during conditions of high physiological stress in free-living environments such as military training. Adv Nutr 2020;00:1-10.
Article
Testosterone supplementation during energy deficit promotes whole-body lean mass accretion, but the mechanisms underlying that effect remain unclear. To elucidate those mechanisms, skeletal muscle molecular adaptations were assessed from muscle biopsies collected before (Resting), 1 h (Post) and 6 h (Recovery) after exercise and a mixed meal (40 g protein, 1 h post-exercise) following 14 days of weight maintenance (WM) and 28 days of an exercise- and diet-induced 55% energy deficit (ED) in 50 physically active, non-obese men treated with 200 mg testosterone enanthate/week (TEST) or placebo (PLA) during the ED. Participants (n=10/group) exhibiting substantial increases (TEST) in leg lean mass and total testosterone were compared to those exhibiting decreases in both of these measures (PLA). Resting androgen receptor (AR) protein content was higher and fibroblast growth factor-inducible 14 (Fn14), IL-6 receptor (IL-6R), and muscle ring-finger protein-1 (MuRF1) gene expression were lower in TEST versus PLA during ED relative to WM (P < 0.05). Changes in inflammatory, myogenic, and proteolytic gene expression did not differ between groups after exercise and recovery feeding. Mechanistic target of rapamycin (mTOR) signaling (i.e., translational efficiency) was also similar between groups at rest and after exercise and the mixed meal. Muscle total RNA content (i.e., translational capacity) increased more during ED in TEST than PLA (P < 0.05). These findings indicate that attenuated proteolysis at rest, possibly downstream of AR, Fn14, and IL-6R signaling, and increased translational capacity, not efficiency, may drive lean mass accretion with testosterone administration during energy deficit.
Article
Background: The erythropoietic cells in the bone marrow require iron to synthesize heme for incorporation into hemoglobin. Exposure to hypoxic conditions, such as extended sojourns to high altitude (HA), results in increased erythropoiesis and an increased physiological requirement for iron. In addition to increasing iron requirements, hypoxic conditions suppress appetite and often lead to decreased energy intake. The objective of this study was to determine the combined effects of severe energy deficit and hypoxia on hepcidin and measures of iron status in lowlanders sojourning to HA. Methods: Iron status indicators and hepcidin were determined in 17 healthy male volunteers (mean ± standard deviation, age 23 ± 6 years, body mass index 27 ± 4 kg/m2) fed a controlled diet (12 ± 1.2 mg iron/day) during a 20-day sojourn to 4300 m above sea level. Results: Chronic exposure to HA during severe energy deficit increased hematocrit by 12% (p < 0.01) and decreased serum hepcidin by 37% (p < 0.01) compared with baseline. Ferritin declined by 18% (p = 0.02) and transferrin saturation and soluble transferrin receptor increased by 55% and 83%, respectively (p < 0.01 for both) compared with baseline. Conclusions: HA acclimatization suppresses hepcidin expression to increase iron availability during severe energy deficit. Registered at ClinicalTrials.gov as NCT02731066.
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Dual amylin and calcitonin receptor agonists (DACRAs) are novel candidates for treatment of T2D and obesity due to their beneficial effects on body weight, blood glucose and insulin sensitivity. DACRAs activate the receptors for a prolonged time period resulting in metabolic effects superior to those of amylin. Pharmacological amylin receptor activation leads to body weight loss and reduced food intake as well as improved food preference, at least short-term. Due to the prolonged receptor activation, different dosing intervals and hence less frequent receptor activation might change the efficacy of DACRA treatment in terms of weight loss and food preference. In this study, we compared daily dosing (q.d.) to dosing every other day (q.a.d.) with the aim of understanding the optimal balance between efficacy and tolerability. Obese and lean male Sprague-Dawley rats were treated with the DACRA, KBP-088, applying two different dosing intervals: 1.5 nmol/kg q.d. and 3 nmol/kg q.a.d, in order to assess the effects on body weight, food intake, glucose tolerance as well as food preference when given the choice between chow (13% fat) and high fat diet (60% fat). Treatment with KBP-088 induced a significant weight loss, reduction in adiposity, improvement in glucose control and altered food preference towards less calorie-dense food. KBP-088 dosed q.a.d. (3 nmol/kg) was superior to KBP-088 q.d. (1.5 nmol/kg) in terms of body weight loss and improvement in food preference. Hence, dosing KBP-088 q.a.d. positively affects overall efficacy on metabolic parameters, suggesting that less frequent dosing with KBP-088 could be feasible. SIGNIFICANCE STATEMENT: Here we show that food preference can be altered chronically towards less calorie-dense choices by pharmacological treatment. Further, pharmacological dosing regimens affects the efficacy differently, as dosing every other day improved body weight loss and alterations in food preference compared to daily dosing. This suggest that alterations of the dosing regimens could be feasible in the treatment of obesity.
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In this study, we compare the effects of isocaloric high (HIGH: 2 g.kg‐1.d‐1, n = 19) and low protein diet (LOW: 1 g.kg‐1.d‐1, n = 19) on changes in body composition, muscle strength, and endocrine variables in response to a 10‐day military field exercise with energy deficit, followed by seven days of recovery. Body composition (DXA), one repetition maximum (1RM) bench and leg press, counter movement jump height (CMJ) and blood variables were assessed before and after the exercise. Performance and blood variables were reassessed after seven days of recovery. The 10‐day exercise resulted in, severe energy deficit in both LOW and HIGH (‐4373 ± 1250, ‐4271 ± 1075 kcal.d‐1), and led to decreased body mass (‐6.1%, ‐5.2%), fat mass (‐40.5%, ‐33.4%), 1RM bench press (‐9.5%, ‐9.7%), 1RM leg press (‐7.8%, ‐8.3%) and CMJ (‐14.7%, ‐14.6%), with no differences between groups. No change was seen for fat free mass. In both groups, the exercise led to a switch towards a catabolic physiological milieu, evident as reduced levels of anabolic hormones (testosterone, IGF‐1) and increased levels of cortisol (more pronounced in HIGH, p<0.05). Both groups also displayed substantial increases in creatine kinase. After seven days of recovery, most variables had returned to close‐to pre‐exercise levels, except for CMJ, which remained at reduced levels. In conclusion, increased protein intake during 10‐day of military field exercise with severe energy deficiency did not mitigate loss of body mass or impairment of physical performance.
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Background: A dietary protein intake higher than the Recommended Dietary Allowance during an energy deficit helps to preserve lean body mass (LBM), particularly when combined with exercise. Objective: The purpose of this study was to conduct a proof-of-principle trial to test whether manipulation of dietary protein intake during a marked energy deficit in addition to intense exercise training would affect changes in body composition. Design: We used a single-blind, randomized, parallel-group prospective trial. During a 4-wk period, we provided hypoenergetic (∼40% reduction compared with requirements) diets providing 33 ± 1 kcal/kg LBM to young men who were randomly assigned (n = 20/group) to consume either a lower-protein (1.2 g · kg(-1) · d(-1)) control diet (CON) or a higher-protein (2.4 g · kg(-1) · d(-1)) diet (PRO). All subjects performed resistance exercise training combined with high-intensity interval training for 6 d/wk. A 4-compartment model assessment of body composition was made pre- and postintervention. Results: As a result of the intervention, LBM increased (P < 0.05) in the PRO group (1.2 ± 1.0 kg) and to a greater extent (P < 0.05) compared with the CON group (0.1 ± 1.0 kg). The PRO group had a greater loss of fat mass than did the CON group (PRO: -4.8 ± 1.6 kg; CON: -3.5 ± 1.4kg; P < 0.05). All measures of exercise performance improved similarly in the PRO and CON groups as a result of the intervention with no effect of protein supplementation. Changes in serum cortisol during the intervention were associated with changes in body fat (r = 0.39, P = 0.01) and LBM (r = -0.34, P = 0.03). Conclusions: Our results showed that, during a marked energy deficit, consumption of a diet containing 2.4 g protein · kg(-1) · d(-1) was more effective than consumption of a diet containing 1.2 g protein · kg(-1) · d(-1) in promoting increases in LBM and losses of fat mass when combined with a high volume of resistance and anaerobic exercise. Changes in serum cortisol were associated with changes in body fat and LBM, but did not explain much variance in either measure. This trial was registered at clinicaltrials.gov as NCT01776359.
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Physiological consequences of winter military operations are not well described. This study examined Norwegian soldiers (n = 21 males) participating in a physically demanding winter training program to evaluate whether short-term military training alters energy and whole-body protein balance, muscle damage, soreness, and performance. Energy expenditure (D2(18)O) and intake were measured daily, and postabsorptive whole-body protein turnover ([(15)N]-glycine), muscle damage, soreness, and performance (vertical jump) were assessed at baseline, following a 4-day, military task training phase (MTT) and after a 3-day, 54-km ski march (SKI). Energy intake (kcal·day(-1)) increased (P < 0.01) from (mean ± SD (95% confidence interval)) 3098 ± 236 (2985, 3212) during MTT to 3461 ± 586 (3178, 3743) during SKI, while protein (g·kg(-1)·day(-1)) intake remained constant (MTT, 1.59 ± 0.33 (1.51, 1.66); and SKI, 1.71 ± 0.55 (1.58, 1.85)). Energy expenditure increased (P < 0.05) during SKI (6851 ± 562 (6580, 7122)) compared with MTT (5480 ± 389 (5293, 5668)) and exceeded energy intake. Protein flux, synthesis, and breakdown were all increased (P < 0.05) 24%, 18%, and 27%, respectively, during SKI compared with baseline and MTT. Whole-body protein balance was lower (P < 0.05) during SKI (-1.41 ± 1.11 (-1.98, -0.84) g·kg(-1)·10 h) than MTT and baseline. Muscle damage and soreness increased and performance decreased progressively (P < 0.05). The physiological consequences observed during short-term winter military training provide the basis for future studies to evaluate nutritional strategies that attenuate protein loss and sustain performance during severe energy deficits.
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Maximizing fat loss while preserving lean tissue mass and function is a central goal of modern obesity treatments. A widely cited rule guiding expected loss of lean tissue as fat-free mass (FFM) states that approximately one-fourth of weight loss will be FFM (i.e. ΔFFM/ΔWeight = ∼0.25), with the remaining three-fourths being fat mass. This review examines the dynamic relationships between FFM, fat mass and weight changes that follow induction of negative energy balance with hypocaloric dieting and/or exercise. Historical developments in the field are traced with the 'Quarter FFM Rule' used as a framework to examine evolving concepts on obesity tissue, excess weight and what is often cited as 'Forbes' Rule'. Temporal effects in the fractional contribution of FFM to changes in body weight are examined as are lean tissue moderating effects such as ageing, inactivity and exercise that frequently accompany structured low-calorie diet weight loss protocols. Losses of lean tissue with dieting typically tend to be small, raising questions about study design, power and applied measurement method reliability. Our review elicits important questions related to the fractional loss of lean tissues with dieting and provides a foundation for future research on this topic.
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To determine whole-body protein turnover responses to high protein diets during weight loss, 39 adults (age, 21±1 yr; VO2peak, 48±1 ml kg(-1) min(-1); body mass index, 25±1 kg m(2)) were randomized to diets providing protein at the recommend dietary allowance (RDA), 2X-RDA, or 3X-RDA. A 10-day weight maintenance period preceded a 21-day, 40% energy deficit. Postabsorptive (FASTED) and postprandial (FED) whole-body protein turnover was determined during weight maintenance (day 10) and energy deficit (day 31) using [1-(13)C]-leucine. FASTED flux, synthesis, and breakdown were lower (P<0.05) for energy deficit than weight maintenance. Protein flux and synthesis were higher (P<0.05) for FED than FASTED. Feeding attenuated (P<0.05) breakdown during weight maintenance but not energy deficit. Oxidation increased (P<0.05) between dietary protein levels, and feeding stimulated oxidation, although oxidative responses to feeding were higher (P<0.05) for energy deficit than weight maintenance. FASTED net balance decreased between dietary protein levels, but in the FED state, net balance was lower for 3X-RDA as compared to RDA and 2X-RDA (diet-by-state, P<0.05). Consuming dietary protein at levels above the RDA, particularly 3X-RDA, during short-term weight loss increases protein oxidation with concomitant reductions in net protein balance.International Journal of Obesity (accepted article preview online, 29 October 2013; doi:10.1038/ijo.2013.197.
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To provide evidence-based guidance regarding the efficacy and safety of dietary protein supplement (PS) use by members of the U.S. Armed Forces, a panel of internationally recognized experts in the fields of protein metabolism and dietary supplement research was convened by the Department of Defense Center Alliance for Dietary Supplement Research and the U.S. Army Medical Research and Material Command. To develop a consensus statement, potential benefits, risks, and strategies to optimize military performance through PS use were considered in the context of specific warfighter populations and occupational demands. To maintain muscle mass, strength, and performance during periods of substantial metabolic demand and concomitant negative energy balance the panel recommended that warfighters consume 1.5-2.0 g ⋅ kg(-1) ⋅ d(-1) of protein. However, if metabolic demand is low, such as in garrison, protein intake should equal the current Military Dietary Reference Intake (0.8-1.5 g ⋅ kg(-1) ⋅ d(-1)). Although PS use generally appears to be safe for healthy adults, warfighters should be educated on PS quality, given quality-control and contamination concerns with commercial dietary supplements. To achieve recommended protein intakes, the panel strongly urges consumption of high-quality protein-containing whole foods. However, when impractical, the use of PSs (20-25 g per serving or 0.25-0.3 g ⋅ kg(-1) per meal), particularly after periods of strenuous physical activity (e.g., military training, combat patrols, and exercise), is acceptable. The committee acknowledges the need for further study of protein requirements for extreme, military-specific environmental conditions and whether unique metabolic stressors associated with military service alter protein requirements for aging warfighters.
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The purpose of this work was to determine the effects of varying levels of dietary protein on body composition and muscle protein synthesis during energy deficit (ED). A randomized controlled trial of 39 adults assigned the subjects diets providing protein at 0.8 (recommended dietary allowance; RDA), 1.6 (2×-RDA), and 2.4 (3×-RDA) g kg(-1) d(-1) for 31 d. A 10-d weight-maintenance (WM) period was followed by a 21 d, 40% ED. Body composition and postabsorptive and postprandial muscle protein synthesis were assessed during WM (d 9-10) and ED (d 30-31). Volunteers lost (P<0.05) 3.2 ± 0.2 kg body weight during ED regardless of dietary protein. The proportion of weight loss due to reductions in fat-free mass was lower (P<0.05) and the loss of fat mass was higher (P<0.05) in those receiving 2×-RDA and 3×-RDA compared to RDA. The anabolic muscle response to a protein-rich meal during ED was not different (P>0.05) from WM for 2×-RDA and 3×-RDA, but was lower during ED than WM for those consuming RDA levels of protein (energy × protein interaction, P<0.05). To assess muscle protein metabolic responses to varied protein intakes during ED, RDA served as the study control. In summary, we determined that consuming dietary protein at levels exceeding the RDA may protect fat-free mass during short-term weight loss.-Pasiakos, S. M., Cao, J. J., Margolis, L. M., Sauter, E. R., Whigham, L. D., McClung, J. P., Rood, J. C., Carbone, J. W., Combs, G. F., Jr., Young, A. J. Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial.
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Fat-free mass (FFM) adaptations to physical training may differ between sexes based on disparities in fitness level, dietary intake, and levels of plasma amino acids (AA). This investigation aimed to determine FFM and plasma AA responses to military training, examine whether adaptations differ between male and female recruits, and explore potential associations between FFM and AA responses to training. Body composition and plasma AA levels were assessed in US Army recruits (n = 209, 118 males, 91 females) before (baseline) and every three weeks during basic combat training (BCT), a 10-week military training course. Body weight decreased in men but remained stable in women during BCT (sex-by-time interaction, P < 0.05). Fifty-eight percent of recruits gained FFM during BCT, with more (P < 0.05) females (88%) gaining FFM than males (36%). Total plasma AA increased (P < 0.05) during BCT, with greater (P < 0.05) increases observed in females (17%) then in males (4%). Essential amino acids (EAA) and branched-chain amino acids (BCAA) were increased (P < 0.05) in females but did not change in males (sex-by-time interaction, P < 0.05). Independent of sex, changes in EAA (r = 0.34) and BCAA (r = 0.27) from baseline were associated with changes in FFM (P < 0.05); greater (P < 0.05) increases in AA concentrations were observed for those who gained FFM. Increases in FFM and plasma AA suggest that BCT elicits a more pronounced anabolic response in women compared to men, which may reflect sex-specific differences in the relative intensity of the combined training and physiological stimulus associated with BCT.
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Background: It is currently unclear whether altering the carbohydrate-to-protein ratio of low-fat, energy-restricted diets augments weight loss and cardiometabolic risk markers. Objective: The objective was to conduct a systematic review and meta-analysis of studies that compared energy-restricted, isocaloric, high-protein, low-fat (HP) diets with standard-protein, low-fat (SP) diets on weight loss, body composition, resting energy expenditure (REE), satiety and appetite, and cardiometabolic risk factors. Design: Systematic searches were conducted by using MEDLINE, EMBASE, PubMed, and the Cochrane Central Register of Controlled Trials to identify weight-loss trials that compared isocalorically prescribed diets matched for fat intake but that differed in protein and carbohydrate intakes in participants aged ≥18 y. Twenty-four trials that included 1063 individuals satisfied the inclusion criteria. Results: Mean (±SD) diet duration was 12.1 ± 9.3 wk. Compared with an SP diet, an HP diet produced more favorable changes in weighted mean differences for reductions in body weight (−0.79 kg; 95% CI: −1.50, −0.08 kg), fat mass (FM; −0.87 kg; 95% CI: −1.26, −0.48 kg), and triglycerides (−0.23 mmol/L; 95% CI: −0.33, −0.12 mmol/L) and mitigation of reductions in fat-free mass (FFM; 0.43 kg; 95% CI: 0.09, 0.78 kg) and REE (595.5 kJ/d; 95% CI: 67.0, 1124.1 kJ/d). Changes in fasting plasma glucose, fasting insulin, blood pressure, and total, LDL, and HDL cholesterol were similar across dietary treatments (P ≥ 0.20). Greater satiety with HP was reported in 3 of 5 studies. Conclusion: Compared with an energy-restricted SP diet, an isocalorically prescribed HP diet provides modest benefits for reductions in body weight, FM, and triglycerides and for mitigating reductions in FFM and REE.
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To examine the influence of dietary protein on lean body mass loss and performance during short-term hypoenergetic weight loss in athletes. In a parallel design, 20 young healthy resistance-trained athletes were examined for energy expenditure for 1 wk and fed a mixed diet (15% protein, 100% energy) in the second week followed by a hypoenergetic diet (60% of the habitual energy intake), containing either 15% (approximately 1.0 g x kg(-1)) protein (control group, n = 10; CP) or 35% (approximately 2.3 g x kg(-1)) protein (high-protein group, n = 10; HP) for 2 wk. Subjects continued their habitual training throughout the study. Total, lean body, and fat mass, performance (squat jump, maximal isometric leg extension, one-repetition maximum (1RM) bench press, muscle endurance bench press, and 30-s Wingate test) and fasting blood samples (glucose, nonesterified fatty acids (NEFA), glycerol, urea, cortisol, free testosterone, free Insulin-like growth factor-1 (IGF-1), and growth hormone), and psychologic measures were examined at the end of each of the 4 wk. Total (-3.0 +/- 0.4 and -1.5 +/- 0.3 kg for the CP and HP, respectively, P = 0.036) and lean body mass loss (-1.6 +/- 0.3 and -0.3 +/- 0.3 kg, P = 0.006) were significantly larger in the CP compared with those in the HP. Fat loss, performance, and most blood parameters were not influenced by the diet. Urea was higher in HP, and NEFA and urea showed a group x time interaction. Fatigue ratings and "worse than normal" scores on the Daily Analysis of Life Demands for Athletes were higher in HP. These results indicate that approximately 2.3 g x kg(-1) or approximately 35% protein was significantly superior to approximately 1.0 g x kg(-1) or approximately 15% energy protein for maintenance of lean body mass in young healthy athletes during short-term hypoenergetic weight loss.
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Body mass loss is inevitable with chronic hypoxic exposure. However, the exact body-composition changes, their causes, and possible treatments remain unknown. The objective was to investigate body composition during a high-altitude expedition by using non-empirically derived methods, experimentally manipulating energy intake, and investigating the influence of initial body composition. Forty-one participants completed a 21-d expedition in the Himalayas. Energy intake was manipulated with a double-blind, placebo-controlled, randomized trial of carbohydrate energy supplementation. Body composition was assessed before and after the expedition by using a 4-component model including fat mass, total body water, bone mineral mass, and residual mass (principally protein and glycogen). Data were analyzed by repeated-measures analysis of variance. Participants allocated to receive carbohydrate were given an additional 15,058 +/- 6211 kcal over the 21-d expedition (>6 kcal x kg(-1) x d(-1)). Nevertheless, the functionally important residual mass decreased in both groups by 6% (main effect of time: P = 0.021), with no effect of allocation (interaction effect: P = 0.116). Similar decreases were observed for fat mass (11%) and total body water (3%), which were also unabated by allocation. Furthermore, high initial fat mass (by median split) did not preserve residual mass (high-fat compared with low-fat participants: residual loss = 5% compared with 8%; P = 0.990). High-altitude exposure decreased body mass, including the functionally important residual component. These losses were not abated by increasing energy intake or an initially high fat mass. Factors other than negative energy balance must contribute to body-composition changes with chronic hypoxia. This trial was registered at clinicaltrials.gov as NCT00731510.
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Diets with increased protein and reduced carbohydrates (PRO) are effective for weight loss, but the long-term effect on maintenance is unknown. This study compared changes in body weight and composition and blood lipids after short-term weight loss (4 mo) followed by weight maintenance (8 mo) using moderate PRO or conventional high-carbohydrate (CHO) diets. Participants (age = 45.4 +/- 1.2 y; BMI = 32.6 +/- 0.8 kg/m(2); n = 130) were randomized to 2 energy-restricted diets (-500 kcal/d or -2093 kJ/d): PRO with 1.6 g x kg(-1) x d(-1) protein and <170 g/d carbohydrates or CHO with 0.8 g x kg(-1) x d(-1) protein, >220 g/d carbohydrates. At 4 mo, the PRO group had lost 22% more fat mass (FM) (-5.6 +/- 0.4 kg) than the CHO group (-4.6 +/- 0.3 kg) but weight loss did not differ between groups (-8.2 +/- 0.5 kg vs. -7.0 +/- 0.5 kg; P = 0.10). At 12 mo, the PRO group had more participants complete the study (64 vs. 45%, P < 0.05) with greater improvement in body composition; however, weight loss did not differ between groups (-10.4 +/- 1.2 kg vs. -8.4 +/- 0.9 kg; P = 0.18). Using a compliance criterion of participants attaining >10% weight loss, the PRO group had more participants (31 vs. 21%) lose more weight (-16.5 +/- 1.5 vs. -12.3 +/- 0.9 kg; P < 0.01) and FM (-11.7 +/- 1.0 vs. -7.9 +/- 0.7 kg; P < 0.01) than the CHO group. The CHO diet reduced serum cholesterol and LDL cholesterol compared with PRO (P < 0.01) at 4 mo, but the effect did not remain at 12 mo. PRO had sustained favorable effects on serum triacylglycerol (TAG), HDL cholesterol (HDL-C), and TAG:HDL-C compared with CHO at 4 and 12 mo (P < 0.01). The PRO diet was more effective for FM loss and body composition improvement during initial weight loss and long-term maintenance and produced sustained reductions in TAG and increases in HDL-C compared with the CHO diet.
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Dual-photon absorptiometry (DPA) allows separation of body mass into bone mineral, fat, and fat-free soft tissue. This report evaluates the potential of DPA to isolate appendages of human subjects and to quantify extremity skeletal muscle mass (limb fat-free soft tissue). The method was evaluated in 34 healthy adults who underwent DPA study, anthropometry of the limbs, and estimation of whole-body skeletal muscle by models based on total body potassium (TBK) and nitrogen (TBN) and on fat-free body mass (FFM). DPA appendicular skeletal muscle (22.0 +/- 3.1 kg, mean +/- SD) represented 38.7% of FFM, with similar proportions in males and females. There were strong correlations (all p less than 0.001) between limb muscle mass estimated by DPA and anthropometric limb muscle areas (r = 0.82-0.92), TBK (r = 0.94), and total-body muscle mass based on TBK-FFM (r = 0.82) and TBK-TBN (r = 0.82) models. Appendicular skeletal muscle mass estimated by DPA is thus a potentially practical and accurate method of quantifying human skeletal muscle mass in vivo.
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Progressive body weight loss occurs during high mountain expeditions, but whether it is due to hypoxia, inadequate diet, malabsorption, or the multiple stresses of the harsh environment is unknown. To determine whether hypoxia due to decompression causes weight loss, six men, provided with a palatable ad libitum diet, were studied during progressive decompression to 240 Torr over 40 days in a hypobaric chamber where hypoxia was the major environmental variable. Caloric intake decreased 43.0% from 3,136 to 1,789 kcal/day (P less than 0.001). The percent carbohydrate in the diet decreased from 62.1 to 53.2% (P less than 0.001). Over the 40 days of the study the subjects lost 7.4 +/- 2.2 (SD) kg and 1.6% (2.5 kg) of the total body weight as fat. Computerized tomographic scans indicated that most of the weight loss was derived from fat-free weight. The data indicated that prolonged exposure to the increasing hypoxia was associated with a reduction in carbohydrate preference and body weight despite access to ample varieties and quantities of food. This study suggested that hypoxia can be sufficient cause for the weight loss and decreased food consumption reported by mountain expeditions at high altitude.
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To test the hypotheses that prolonged exposure to moderately high altitude increases the energy requirement of adequately fed women and that the sole cause of the increase is an elevation in basal metabolic rate (BMR), we studied 16 healthy women [21.7 +/- 0.5 (SD) yr; 167.4 +/- 1.1 cm; 62.2 +/- 1.0 kg]. Studies were conducted over 12 days at sea level (SL) and at 4,300 m [high altitude (HA)]. To test that menstrual cycle phase has an effect on energetics at HA, we monitored menstrual cycle in all women, and most women (n = 11) were studied in the same phase at SL and HA. Daily energy intake at HA was increased to respond to increases in BMR and to maintain body weight and body composition. Mean BMR for the group rose 6.9% above SL by day 3 at HA and fell to SL values by day 6. Total energy requirement remained elevated 6% at HA [ approximately 670 kJ/day (160 kcal/day) above that at SL], but the small and transient increase in BMR could not explain all of this increase, giving rise to an apparent "energy requirement excess." The transient nature of the rise in BMR may have been due to the fitness level of the subjects. The response to altitude was not affected by menstrual cycle phase. The energy requirement excess is at present unexplained.
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Testosterone increases muscle mass and strength and regulates other physiological processes, but we do not know whether testosterone effects are dose dependent and whether dose requirements for maintaining various androgen-dependent processes are similar. To determine the effects of graded doses of testosterone on body composition, muscle size, strength, power, sexual and cognitive functions, prostate-specific antigen (PSA), plasma lipids, hemoglobin, and insulin-like growth factor I (IGF-I) levels, 61 eugonadal men, 18-35 yr, were randomized to one of five groups to receive monthly injections of a long-acting gonadotropin-releasing hormone (GnRH) agonist, to suppress endogenous testosterone secretion, and weekly injections of 25, 50, 125, 300, or 600 mg of testosterone enanthate for 20 wk. Energy and protein intakes were standardized. The administration of the GnRH agonist plus graded doses of testosterone resulted in mean nadir testosterone concentrations of 253, 306, 542, 1,345, and 2,370 ng/dl at the 25-, 50-, 125-, 300-, and 600-mg doses, respectively. Fat-free mass increased dose dependently in men receiving 125, 300, or 600 mg of testosterone weekly (change +3.4, 5.2, and 7.9 kg, respectively). The changes in fat-free mass were highly dependent on testosterone dose (P = 0.0001) and correlated with log testosterone concentrations (r = 0.73, P = 0.0001). Changes in leg press strength, leg power, thigh and quadriceps muscle volumes, hemoglobin, and IGF-I were positively correlated with testosterone concentrations, whereas changes in fat mass and plasma high-density lipoprotein (HDL) cholesterol were negatively correlated. Sexual function, visual-spatial cognition and mood, and PSA levels did not change significantly at any dose. We conclude that changes in circulating testosterone concentrations, induced by GnRH agonist and testosterone administration, are associated with testosterone dose- and concentration-dependent changes in fat-free mass, muscle size, strength and power, fat mass, hemoglobin, HDL cholesterol, and IGF-I levels, in conformity with a single linear dose-response relationship. However, different androgen-dependent processes have different testosterone dose-response relationships.
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Negative energy balance during military operations can be severe and result in significant reductions in fat-free mass (FFM). Consuming supplemental high-quality protein following such military operations may accelerate restoration of FFM. Body composition (dual-energy x-ray absorptiometry) and whole-body protein turnover (single-pool (15)N-alanine method) were determined before (PRE) and after 7 d (POST) of severe negative energy balance during military training in 63 male US Marines (mean±SD, 25±3 y, 84±9 kg). After POST measures were collected, volunteers were randomized to receive higher-protein (HIGH: 1103 kcal/d, 133 g protein/d), moderate protein (MOD: 974 kcal/d, 84 g protein/d), or carbohydrate-based low protein control (CON: 1042 kcal/d, 7 g protein/d) supplements, in addition to a self-selected, ad libitum diet, for the 27 d intervention (REFED). Measurements were repeated POST-REFED. POST total body mass (TBM, -5.8±1.0 kg, -7.0%), FFM (-3.1±1.6 kg, -4.7%), and net protein balance (-1.7±1.1 g protein/kg/d) were lower and proteolysis (1.1±1.9 g protein/kg/d) was higher compared to PRE (P<0.05). Self-selected, ad libitum dietary intake during REFED was similar between groups (3507 ± 730 kcal/d, 2.0±0.5 g protein/kg/d). However, diets differed by protein intake due to supplementation (CON: 2.0±0.4, MOD: 3.2±0.7, HIGH: 3.5±0.7 g/kg/d; P<0.05) but not total energy (4498±725 kcal/d). All volunteers, independent of group assignment, achieved positive net protein balance (0.4±1.0 g protein/kg/d) and gained TBM (5.9±1.7 kg, 7.8%) and FFM (3.6±1.8 kg, 5.7%) POST-REFED compared to POST (P<0.05). Supplementing ad libitum, energy-adequate, higher-protein diets with additional protein may not be necessary to restore FFM after short-term severe negative energy balance.
Article
Purpose: Determine if providing supplemental nutrition spares whole-body protein by attenuating the level of negative energy balance induced by military training, and to assess whether protein balance is differentially influenced by macronutrient source. Methods: Soldiers participating in 4-d arctic military training (AMT, 51 km ski march) randomized to receive 3 combat rations (CON; n = 18); 3 combat rations plus 4, 20g, 250 kcal protein-based bars (PRO; n = 28); or 3 combat rations plus 4, 48g, 250 kcal carbohydrate-based bars daily (CHO; n = 27). Energy expenditure (D2 O) and energy intake were measured daily. Nitrogen balance (NBAL) and protein turnover were determined at baseline (BL) and day 3 of AMT using 24 h urine and [N]-glycine. Results: Protein and carbohydrate intake were highest (P < 0.05) for PRO (mean ± SD, 2.0 ± 0.3 g[BULLET OPERATOR]kg[BULLET OPERATOR]d) and CHO (5.8 ± 1.3 g[BULLET OPERATOR]kg[BULLET OPERATOR]d), but only CHO increased (P < 0.05) energy intake above CON. Energy expenditure (6155 ± 515 kcal·d), energy balance (-3313 ± 776 kcal·d), net protein balance (NET; -0.24 ± 0.60 g·d), and NBAL (-68.5 ± 94.6 mg·kg·d) during AMT were similar between groups. In the combined cohort, energy intake was associated (P < 0.05) with NET (r = 0.56) and NBAL (r = 0.69) and Soldiers with the highest energy intake (3723 ± 359 kcal·d, 2.11 ± 0.45 g protein[BULLET OPERATOR]kg[BULLET OPERATOR]d, 6.654 ± 1.16 g carbohydrate[BULLET OPERATOR]kg[BULLET OPERATOR]d) achieved net protein balance and NBAL during AMT. Conclusion: These data reinforce the importance of consuming sufficient energy during periods of high energy expenditure to mitigate the consequences of negative energy balance and attenuate whole-body protein loss.
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Accurate prediction of the metabolic energy walking requires can inform numerous health, bodily status and fitness outcomes. Here, we adopted a two-step approach to identifying a concise, generalized equation for predicting level human walking metabolism. Using literature-aggregated values, we compared: 1) the predictive accuracy of three literature equations: ACSM, Pandolf, and Height-Weight-Speed (HWS) equations, and 2) the goodness-of-fit possible from one- vs. two-component descriptions of walking metabolism. Literature metabolic rate values (n=127; speed range=0.4-1.9 m∙s(-1)) were aggregated from 25 subject populations (n=5-42) whose means spanned a 1.8-fold range of heights and a 4.2-fold range of weights. Population-specific resting metabolic rates (VO2-rest) were determined using standardized equations. Our first finding was that the ACSM and Pandolf equations under-predicted nearly all 127 literature-aggregated values. Consequently, their standard errors of estimate (SEE) were nearly four times greater than those of the HWS equation (4.51 and 4.39 vs. 1.13 mls O2∙kg(-1)∙min(-1), respectively). For our second comparison, empirical best-fit relationships for walking metabolism were derived from the data set in one- and two-component forms for three VO2-speed model types: linear (∝V(1.0)), exponential (∝V(2.0)), and exponential/height (∝V(2.0)/Ht). We found that the proportion of variance (R(2)) accounted for, when averaged across the three model types, was substantially lower for one- vs. two-component versions (0.63±0.1 vs. 0.90±0.03) and the predictive errors were nearly twice as great (SEE=2.22 vs. 1.21 mls O2∙kg(-1)∙min(-1)). Our final analysis identified the following concise, generalized equation for predicting level human walking metabolism: VO2-total=VO2-rest+3.85+5.97∙V(2)/Ht (units: V, m∙s(-1); Ht, m; and VO2, mls O2∙kg(-1)∙min(-1)).
Article
Methods: Forty-eight trekkers were studied during a progressive trek at 3833, 4450, and 5129 m at rest postascent (exercise), and then again at rest 24 hours later. Twenty of the subjects were also tested at rest pre- and postexercise at sea level (SL) at 6 weeks preascent. We examined plasma levels of the interleukin 6 (IL-6), 17a (IL-17a), and endothelin-1 (ET-1) along with oxygen saturation (SpO2) and Lake Louise scores (LLS). Results: ET-1 (5.7 ± 2.1 vs. 4.3 ± 1.9 pg/mL; p < 0.001), IL-6 (3.3 ± 3.3 vs. 2.4 ± 2.3 pg/mL; p = 0.007), and IL-17a (1.3 ± 3.0 vs. 0.46 ± 0.4 pg/mL; p < 0.001) were all overall significantly higher at HA versus SL. There was a paired increase in ET-1 and IL-6 with exercise versus rest at SL, 3833, 4450, and 5129 m (p < 0.05). There was a negative correlation between LLS and SpO2 (r = -0.32; 95% confidence interval [CI] -0.21 to -0.42; p < 0.001) and a positive correlation between LLS and IL-6 (r = 0.16; 0.0-0.27; p = 0.007) and ET-1 levels (r = 0.29; 0.18-0.39; p < 0.001. Altitude, ET-1, IL-6, and SpO2 were all univariate predictors of AMS. On multivariate analysis, ET-1 (p = 0.002) and reducing SpO2 (p = 0.02) remained as the only independent predictors (overall r(2) = 0.16; p < 0.001) of AMS. ET-1 (p = 03) and SpO2 were (p = 0.01) also independent predictors of severe AMS (overall r(2) = 0.19; p < 0.001). Conclusions: HA leads to endothelial activation and an inflammatory response. The rise in ET-1 and IL-6 is heavily influenced by the degree of exercise and hypoxia. ET-1 is an independent predictor of both AMS and its severity.
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Zaccagni, Luciana, Davide Barbieri, Annalisa Cogo, and Emanuela Gualdi-Russo. Anthropometric and body composition changes during expeditions at high altitude. High Alt Med Biol 15:000—000, 2014.—The purpose of this study is to investigate separately in the two sexes the physical adaptations associated to exposure to high altitude in a sample of 18 nonacclimatized Caucasian subjects (10 males and 8 females, 22–59 years) who participated to scientific expeditions to Himalaya up to the Pyramid Laboratory (5050m, Nepal) or Everest North Base Camp (5300m, Tibet). Anthropometric traits (body height and weight, eight girths and six skinfolds) were collected according to standard procedures, before departure at sea level, during ascent (at altitude > 4000m above sea level), and after return to low altitude. Body composition was assessed by means of the skinfold method. Both sexes lost on average 4.0% of initial body mass, corresponding to 7.6% of fat mass and 3.5% of fat free mass in males, and to 5.0% of fat mass and 3.6% of fat free mass in females. Average fat mass loss was greater in males than in females. Initial fat mass percentage was positively correlated to fat mass loss and negatively to FFM loss in males only, thus at HA leanest subjects lost more FFM and less FM than the fattest ones. Adaptations were faster in males than in females. In conclusion, the present research describes significant adaptations to high altitude, in terms of body weight reduction, regardless of the amount of performed physical activity. Key Words: expeditions to high altitude, Mount Everest, weight loss, women at high altitude
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Loss of body weight and fat-free mass (FFM) are commonly noted with prolonged exposure to hypobaric hypoxia. Recent evidence suggests protein supplementation, specifically leucine, may potentially attenuate loss of FFM in subcaloric conditions during normoxia. The purpose of this study was to determine if leucine supplementation would prevent the loss of FFM in subcaloric conditions during prolonged hypoxia. Eighteen physically active male (n = 10) and female (n = 8) trekkers completed a 13-day trek in Nepal to Everest Base Camp with a mean altitude of 4140 m (range 2810-5364 m). In this double-blind study, participants were randomized to ingest either leucine (LEU) (7 g leucine, 93 kcal, 14.5 g whey-based protein) or an isocaloric isonitrogenous control (CON) (0.3 g LEU, 93 kcal, 11.3 g collagen protein) twice daily prior to meals. Body weight, body composition, and circumferences of bicep, thigh, and calf were measured pre- and post-trek. There was a significant time effect for body weight (-2.2% ± 1.7%), FFM (-1.7% ± 1.5%), fat mass (-4.0% ± 6.9%), and circumferences (p < 0.05). However, there was no treatment effect on body weight (CON -2.3 ± 2.0%; LEU -2.2 ± 1.5%), FFM (CON -2.1 ± 1.5%; LEU -1.2 ± 1.6%), fat mass (CON -2.9% ± 5.9%; LEU -5.4% ± 8.1%), or circumferences. Although a significant loss of body weight, FFM, and fat mass was noted in 13 days of high altitude exposure, FFM loss was not attenuated by leucine. Future studies are needed to determine if leucine attenuates loss of FFM with longer duration high altitude exposure.
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The results of a field study of the energy cost of downhill walking and load carriage were used to test a modification of the Pandolf equation (PE) for the prediction of downhill load carriage energy costs. PE is a predictive equation for the energy cost of walking and load carriage on level and uphill terrain. The field study objective was to broaden the database to include slower walking speeds. A new dataset was collected in the field with loads of 0 kg and 27.2 kg at speeds of 0.89 m(x)/s and 1.12 m(x)s- on grades of 0%, -4%, -8.6% and -10.2%. Oxygen uptake was collected using portable oxygen monitors. To adjust the PE for downhill movement, a correction factor (CF) was derived using data from a prior laboratory study. The final equation is CF = hx(Gx(W+L)xV)/3.5 - ((W+L)x(G+6)2)/W) + (25-v2). The adjusted values, using the M = PE - CF format, fit well for walking at 1.12 m(dot)/s, but at 0.89 m(dot)/s, values were underestimated. Thus, an adjusted PE derived from a laboratory study for walking, and load carriage was valid at 1.12 m(dot)/s for loads up to 27 kg, but was not acceptable at 0.89 m(dot)/s.
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Missions conducted by the U.S. Military during combat involve a multitude of operational stressors that can cause deterioration in physical and military performance of soldiers. Physiological consequences of sustained operational stress include decrements in anabolic hormones, skeletal muscle mass, and loss of bone mineral density. The objective of this review is to examine the current literature and provide commanders with information on the physical and physiological decrements in soldiers conducting sustained operations. The intent is that this will provide commanders with insight on how to plan for missions to incorporate possible countermeasures to enhance or sustain warfighter performance.
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The Compendium of Physical Activities was developed to enhance the comparability of results across studies using self-report physical activity (PA) and is used to quantify the energy cost of a wide variety of PA. We provide the second update of the Compendium, called the 2011 Compendium. The 2011 Compendium retains the previous coding scheme to identify the major category headings and specific PA by their rate of energy expenditure in MET. Modifications in the 2011 Compendium include cataloging measured MET values and their source references, when available; addition of new codes and specific activities; an update of the Compendium tracking guide that links information in the 1993, 2000, and 2011 compendia versions; and the creation of a Web site to facilitate easy access and downloading of Compendium documents. Measured MET values were obtained from a systematic search of databases using defined key words. The 2011 Compendium contains 821 codes for specific activities. Two hundred seventeen new codes were added, 68% (561/821) of which have measured MET values. Approximately half (317/604) of the codes from the 2000 Compendium were modified to improve the definitions and/or to consolidate specific activities and to update estimated MET values where measured values did not exist. Updated MET values accounted for 73% of all code changes. The Compendium is used globally to quantify the energy cost of PA in adults for surveillance activities, research studies, and, in clinical settings, to write PA recommendations and to assess energy expenditure in individuals. The 2011 Compendium is an update of a system for quantifying the energy cost of adult human PA and is a living document that is moving in the direction of being 100% evidence based.