Stefan Pasiakos

U.S. Army Research Institute of Environmental Medicine · Military Performance Division

Background Short-term starvation and severe food deprivation (FD) reduce dietary iron absorption and restricts iron to tissues, thereby limiting the amount of iron available for erythropoiesis. These effects may be mediated by increases in the iron regulatory hormone hepcidin; however, whether mild-to-moderate FD has similar effects on hepcidin and...

Context: Male military personnel conducting strenuous operations experience reduced testosterone, muscle mass, and performance. Pharmacological restoration of normal testosterone may attenuate performance decrements by mitigating muscle loss. Previously, administering testosterone enanthate (200 mg/week) during energy deficit prompted supraphysiol...

Purpose of review: To highlight contemporary findings comparing the digestibility of animal and plant proteins, their stimulatory effects on muscle protein synthesis, and associations with sarcopenia. Recent findings: Animal proteins are more digestible than plant proteins, resulting in greater amino acid availability and stimulation of muscle p...

Objectives Little is known about the relationships between habitual essential amino acid (EAA) intake and functional health in older US adults. This cross-sectional study investigates associations between usual EAA intakes and body composition, muscle strength, and physical function in US adults ≥65 y. Methods The Food and Nutrient Database for Di...

Objectives The lack of complete amino acid composition data in food composition databases has made determining population-wide amino acid intake difficult. This cross-sectional study characterizes habitual intakes of each amino acid and adherence to dietary requirements for each essential amino acid (EAA) by age, gender, and race/ethnicity in the U...

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 wa...

Background Physical and psychological stress alter gut-brain axis activity, potentially causing intestinal barrier dysfunction that may, in turn, induce cognitive and mood impairments through exacerbated inflammation and blood brain barrier (BBB) permeability. These interactions are commonly studied in animals or artificial laboratory environments....

Increasing dietary protein intake during periods of muscle disuse may mitigate the resulting decline in muscle protein synthesis (MPS). The purpose of this randomized pilot study was to determine the effect of increased protein intake during periods of disuse before anterior cruciate ligament (ACL) reconstruction on myofibrillar protein synthesis (...

Background The effects of ingesting varying essential amino acid (EAA)/protein-containing food formats on protein kinetics during energy deficit are undetermined. Therefore, recommendations for EAA/protein food formats necessary to optimize both whole-body protein balance and muscle protein synthesis (MPS) during energy deficit are unknown. We meas...

Background The effects of low muscle glycogen on molecular markers of protein synthesis and myogenesis before and during aerobic exercise with carbohydrate ingestion is unclear. The purpose of this study was to determine the effects of initiating aerobic exercise with low muscle glycogen on mTORC1 signaling and markers of myogenesis. Methods Eleve...

This study used global metabolomics to identify metabolic factors that might contribute to muscle anabolic resistance, which develops when aerobic exercise is initiated with low muscle glycogen using global metabolomics. Eleven men completed this randomized, crossover study, completing two cycle ergometry glycogen depletion trials, followed by 24 h...

Dictionary learning and sparse coding techniques overcome limitations of traditional voxel-level analyses of task-based functional magnetic resonance imaging (fMRI) data by identifying broader temporal and spatial patterns of brain activity. However, prior applications of these methods to task-related fMRI data are not simultaneously optimized to f...

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 environmenta...

Protein quality is an important component of protein intake to support growth, development, and maintenance of essential body tissues and functions. Therefore, protein quality should be emphasized as a key characteristic during protein food selection within the larger context of healthy dietary patterns, especially when considering the wide varianc...

Background: Ramadan fasting (RF) is a form of intermittent fasting that generally improves body composition and related metabolic profiles. Whether RF exacerbates depressive symptomatology in individuals diagnosed with major depressive disorder (MDD) is undetermined. Methods: 100 men, who lived in Bahrain and were between the ages of 18 and 64 y...

Muscle quality (MQ), defined as the amount of strength and/or power per unit of muscle mass, is a novel index of functional capacity that is increasingly relied upon as a critical biomarker of muscle health in low functioning aging and pathophysiological adult populations. Understanding the phenotypical attributes of MQ and how to use it as an asse...

Appropriate nutrition recommendations are required to optimise the health and performance of military personnel, yet limited data are available on whether male and female military personnel have different nutrition requirements. Objectives To consider the evidence for sex-specific nutrition requirements to optimise the health and performance of mi...

Background Clinical administration of testosterone is widely used due to a variety of claimed physical and cognitive benefits. Testosterone administration is associated with enhanced brain and cognitive function, as well as mood, in energy-balanced males, although such relationships are controversial. However, the effects of testosterone administra...

Introduction Anthropometrics and body composition characteristics differentiate many types of athletes and are related to performance on fitness tests and tasks in military personnel. Soldiers competing to enter elite units must demonstrate physical fitness and operational competence across multiple events. Therefore, this study determined whether...

Purpose of review: To highlight emerging evidence challenging traditional recommendations to increase carbohydrate intake to optimize performance at high altitude. Recent findings: Several studies have now clearly demonstrated that, compared with sea level, exogenous carbohydrate oxidation during aerobic exercise is blunted in lowlanders during...

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 limit...

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...

Objectives Secretory IgA (SIgA) is a critical component of mucosal immunity and a first line of defense against pathogens. Intense physical exercise, lack of sleep, and inadequate energy intake are frequently observed during military training and operations. These factors are associated with a decline in SIgA and may increase the risk of infection;...

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...

Background & Aims Protein intake is inversely associated with waist circumference and positively associated with HDL-cholesterol concentrations. However, the relationship between protein intake during specific eating occasions and cardiometabolic health is not well documented. This cross-sectional study measured protein intake at meals and combined...

Energy deficit is common during prolonged periods of strenuous physical activity and limited sleep, but the extent to which appetite suppression contributes is unclear. The aim of this randomized crossover study was to determine the effects of energy balance on appetite and physiologic mediators of appetite during a 72-hr period of high physical ac...

Ingesting protein-containing supplements and foods provides essential amino acids (EAA) necessary to increase muscle and whole-body protein synthesis (WBPS). Large variations exist in the EAA composition of supplements and foods, ranging from free-form amino acids to whole protein foods. We sought to investigate how changes in peripheral EAA after...

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: T...

Background Strenuous physical activity promotes inflammation and depletes muscle glycogen, which may increase the iron regulatory hormone hepcidin. Hepcidin reduces dietary iron absorption and may contribute to declines in iron status frequently observed following strenuous physical activity. Objectives To determine the effects of strenuous physic...

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 acce...

Evidence suggests that carbohydrate and protein (CHO-PRO) ingestion after exercise enhances muscle glycogen repletion to a greater extent than carbohydrate (CHO) alone. However, there is no consensus at this point, and results across studies are mixed, which may be attributable to differences in energy content and carbohydrate intake relative to bo...

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, specificall...

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...

Testosterone (T) administration (TA) increases serum T and fat-free mass (FFM). Although TA-mediated increases in FFM may enhance physical performance, the data are largely equivocal, which may be due to differences in study populations, the magnitude of change in serum T and FFM, or the performance metrics. This meta-analysis explored effects of T...

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...

Objectives Maintaining low muscle glycogen content during recovery from aerobic exercise with low carbohydrate, high fat feeding has been shown to reduce insulin-mediated anabolic signaling compared to high carbohydrate feeding. The effects of low muscle glycogen content on intracellular regulators of muscle mass before and after aerobic exercise w...

Objectives Obesity is associated with increased hepatic de novo lipogenesis (DNL) and altered triglyceride (TG) turnover. A previous trial in male Sprague Dawley rats demonstrated that both energy restriction and higher protein diets downregulate hepatic DNL. It is unknown whether energy restriction and higher protein diets alter kinetic measures o...

Objectives We reported that healthy males supplemented with testosterone gained lean body mass (LBM) during 28-d of energy deficit and 14 d of ad libitium feeding when measured by dual energy x-ray absorptiometry (DXA), but with no increase in muscle strength. We were unable to determine whether LBM gains were due to muscle mass accrual since DXA d...

Objectives High protein (HP) diets during short-term energy restriction (ER) attenuate energy-mediated reductions in muscle protein synthesis (MPS). MPS-adaptive responses to HP diets during prolonged ER are not well described. This study examined the effects of prolonged ER and HP on MPS and the synthesis rates of numerous individual muscle protei...

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 t...

Objectives The Dietary Guidelines for Americans (DGAs) recommend dietary patterns that limit added sugar, sodium, and saturated fat and emphasize nutrient-dense foods. It is unknown whether individuals who self-report adhering to a diet that alters nutrient intake are, in fact, meeting DGA recommendations. Objective: To compare dietary intakes and...

Objectives Iron status declines with military training; however, the reason for the decline is not known. The objective of this study was to determine whether dietary iron absorption is reduced following military training and whether energy deficit during training modifies the effect. Methods This was a randomized, cross-over, controlled-feeding t...

Editorial on writing reviews for the British Journal of Nutrition - Volume 123 Issue 9 - Barbara A. Fielding, Jean-Paul Lalles, Gerald E. Lobley, Stefan M. Pasiakos, Susan J. Whiting

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 cond...

Background: The optimal macronutrient composition of the diet is controversial and many adults attempt to regulate the intake of specific macronutrients for various health-related reasons. Objective: The objective was to compare stability and ranges of intakes of different macronutrients across diverse adult populations in the USA and globally....

Muscle atrophy and weakness occur as a consequence of disuse after musculoskeletal injury (MSI). The slow recovery and persistence of these deficits even after physical rehabilitation efforts indicate that interventions designed to attenuate muscle atrophy and protect muscle function are necessary to accelerate and optimize recovery from MSI. Evide...

Background Severe energy deficits cause interrelated reductions in testosterone and fat free mass. Testosterone supplementation may mitigate those decrements, but could also reduce circulating concentrations of the orexigenic hormone ghrelin thereby exacerbating energy deficit by suppressing appetite. Objective To determine whether testosterone su...

A transient increase in local pro-inflammatory cytokine expression following skeletal muscle injury mediates the repair and regeneration of damaged myofibers through myogenesis. Regenerative capacity is diminished and muscle wasting occurs, however, when intramuscular inflammatory signaling is exceedingly high or persists chronically. An excessive...

Context Severe energy deprivation markedly inhibits erythropoiesis by restricting iron availability for hemoglobin synthesis. Objective The objective of this study was to determine whether testosterone supplementation during energy deficit increased indicators of iron turnover and attenuated the decline in erythropoiesis compared to placebo. Desi...

A recently published meta-analysis in this journal analyzed findings from studies comparing substrate use during exercise at the same relative intensity (i.e., % V̇O2max) in normoxic and hypoxic conditions. The primary conclusion was that hypoxia had no consistent effects on the contribution of carbohydrate oxidation to total energy expenditure. Ho...

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 sele...

Background: Exogenous carbohydrate oxidation is lower during steady-state aerobic exercise in native lowlanders sojourning at high altitude (HA) compared to sea level (SL). However, the underlying mechanism contributing to reduction in exogenous carbohydrate oxidation during steady-state aerobic exercise performed at HA have not been explored. Ob...

This study assessed predictors of successful selection in the very challenging and stressful United States Army Special Forces Assessment and Selection (SFAS) course among 800 Soldiers. A battery of measures were collected during the course and their ability to predict selection were assessed using logistic regression and chi-square tests. Physical...

Purpose: This study determined associations between diet quality measured by the Healthy Eating Index (HEI)-2015, physical performance, and successful selection following a U.S. Army Special Forces Assessment and Selection (SFAS) course characterized by arduous cognitive and physical demands. Methods: HEI-2015 scores were calculated from usual d...

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...

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-concep...

Military personnel and emergency responders perform cognitively-demanding tasks during periods of sustained physical exertion and limited caloric intake. Cognitive function is preserved during short-term caloric restriction, but it is unclear if preservation extends to combined caloric restriction and physical exertion. According to the “reticular-...

Objectives: Greater protein intakes have been associated with decreased weight, BMI, waist circumference (WC) and increased HDL-cholesterol (HDL-C) concentrations. However, the relationship between protein intake during specific eating occasions and metabolic health is not well described. This study measured protein intake at meals (breakfast, lun...