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Level of dietary protein impacts whole body protein turnover in trained males at rest
Abstract
The current investigation examined the effect of variations in protein intake on Whole body protein turnover (WBPTO) at rest in endurance-trained males. Whole body protein turnover is influenced by both diet and exercise. Whether endurance athletes require more protein than the non-exerciser remains equivocal. Five male runners (21.3 +/- 0.3 years, 179 +/- 2 cm, 70.6 +/- 0.1 kg, 8.7% +/- 0.4% body fat, 70.6 +/- 0.1 VO(2)max) participated in a randomized, crossover design diet intervention where they consumed either a low-protein (LP; 0.8 g/kg), moderate-protein (MP; 1.8 g/kg), or high-protein (HP; 3.6 g/kg) diet for 3 weeks. Whole body protein turnover (Ra, leucine rate of appearance; NOLD, nonoxidative leucine disposal; and Ox, leucine oxidation), nitrogen balance, and substrate oxidation were assessed at rest following each dietary intervention period. The HP diet increased leucine Ra (indicator of protein breakdown; 136.7 +/- 9.3, 129.1 +/- 7.4, and 107.8 +/- 3.1 micromol/[kg . h] for HP, MP, and LP diets, respectively) and leucine Ox (31.0 +/- 3.6, 26.2 +/- 4.3, and 18.3 +/- 0.6 micromol/[kg . h] for HP, MP, and LP diets, respectively) compared with LP diet (P < .05). No differences were noted in nonoxidative leucine disposal (an indicator of protein synthesis) across diets. Nitrogen balance was greater for HP diet than for MP and LP diets (10.2 +/- 0.7, 1.8 +/- 0.6, and -0.3 +/- 0.5 for HP, MP, and LP diets, respectively). Protein oxidation increased with increasing protein intake (54% +/- 6%, 25% +/- 1%, and 14% +/- 2% for HP, MP, and LP diets, respectively). Findings from this study show that variations in protein intake can modulate WBPTO and that protein intake approximating the current recommended dietary allowance was not sufficient to achieve nitrogen balance in the endurance-trained males in this investigation. Our results suggest that a protein intake of 1.2 g/kg or 10% of total energy intake is needed to achieve a positive nitrogen balance. This is not a concern for most endurance athletes who routinely consume protein at or above this level.
... We (6) and others (5) have used the indicator amino acid oxidation (IAAO) method to determine protein requirements that would minimize the oxidation of the indicator AA, phenylalanine, suggesting maximal rates of whole-body protein synthesis (13) in male endurance athletes. Using this method, we demonstrated that protein intake should approximate 1.83 g·kg −1 ·d −1 during recovery from a 20-km run for male endurance athletes (6), an amount closer to the higher end of current position stand recommendations (1) and~50% greater than both the recommended intake determined by nitrogen balance in endurance athletes (4,14) and by IAAO in nonexercising adults (15). ...
... In light of the noted research restrictions, retrospective analysis revealed that the biphase breakpoint (i.e., estimated average intake to maximize whole-body protein synthesis) was similar when only using two suboptimal protein intakes and one intake above the breakpoint at the plateau (unpublished analysis), suggesting that individualized breakpoints may be estimated from only three protein intakes. The three protein intakes were selected to correspond to 1) a suboptimal intake to allow for the determination of the slope of the biphasic regression (0.2 g·kg −1 ·d −1 ), 2) the lower boundary of the ACSM recommendations (1) and the recommended intake in endurance athletes determined by nitrogen balance (4,14) as well as the recommended intake determined by IAAO in nonexercising adults (1.2 g·kg −1 ·d −1 ) (1,15), and 3) an intake above our previously determined recommended intake (i.e., the upper 95% confidence interval [CI]) in endurance-trained men by IAAO as well as the upper boundary of the ACSM guidelines (2.0 g·kg −1 ·d −1 ) (1,6). ...
... By deploying the IAAO methodology to a home-based setting and purposely selecting our moderate and surfeit protein intakes (i.e., 1.2 and 2.0 g·kg BM −1 ·d −1 ), the lower PheOx on the highest protein intake demonstrates that current protein recommendations for endurance athletes (1,2,4,14) do not maximize whole-body protein synthesis during an ecologically valid training model. The breakpoint and recommended intakes for F 13 CO 2 and PheOx, which were not different between sexes, suggest that a protein intake of~1.85 g·kg BM −1 ·d −1 maximizes whole-body protein synthesis in trained male and female athletes after an exercise stimulus comparable with the average training session of marathoners with a completion time of <4-h (i.e.,~16 km,~96 min,~5.5 min·km −1 ,~61%VO 2max ) (40). ...
Purpose:
This study aimed to determine the daily protein requirements of female and male endurance athletes in a home-based setting using noninvasive stable isotope methodology (i.e., indicator amino acid oxidation).
Methods:
Eight males (30 ± 3 yr; 78.6 ± 10.5 kg; 75.6 ± 7.5 mL·kgFFM-1·min-1; mean ± SD) and seven females (30 ± 4 yr; 57.7 ± 5.0 kg; 77.5 ± 7.1 mL·kgFFM-1·min-1) during the midluteal phase were studied. After 2 d of controlled diet (1.4 gprotein·kg-1·d-1) and training (10 and 5 km run·d-1, respectively), participants completed a 20-km run before an at-home indicator amino acid oxidation trial testing a suboptimal, a moderate, and an excess (i.e., 0.2, 1.2, and 2.0 g·kg-1·d-1, respectively) protein intake. Protein was consumed as a crystalline amino acid mixture containing [1-13C]phenylalanine to examine whole-body phenylalanine flux and phenylalanine oxidation (PheOx; the reciprocal of whole-body protein synthesis) through breath and urine sample collection. A modified biphasic linear regression determined the breakpoint in PheOx for each participant to generate an estimated average intake that would maximize whole-body protein synthesis for each sex.
Results:
PheOx was different (P < 0.01) between all protein intakes with no effect of sex (P = 0.63). Using a modified three-point curve resulted in a breakpoint that was not different (P = 0.94) between males and females (1.60 and 1.61 g·kg-1·d-1, respectively). The recommended intake (i.e., upper 95% confidence interval) was estimated to be 1.81 and 1.89 g·kg-1·d-1 for males and females, respectively.
Conclusions:
Our findings indicate that endurance athletes consuming a daily protein intake toward the upper end of current consensus recommendations (~1.85 g·kg-1·d-1) will maximize whole-body protein synthesis during postexercise recovery regardless of sex.
... g·kg -1 body weight·d -1 (1). In the case of endurance athletes, these recommendations are largely based on research examining protein intakes required to achieve nitrogen balance (NBAL) (4,5), which as a method may underestimate true requirements (6). ...
... NBAL of 0.94 g·kg -1 ·d -1 with a recommended dietary allowance (RDA) suggested to cover 97.5% of the population at 1.26 g·kg -1 ·d -1 , which is similar to other reports (5). However, identification of a protein intake that maintains NBAL without an appreciation for whether it can also optimize whole body protein metabolism or, more importantly from an athlete perspective, training quality and exercise performance may not provide the athlete with the most relevant nutritional advice (7). ...
... The LOW diet represents the estimated average requirement for endurance athletes as determined by nitrogen balance (4) and a safe intake for non-exercising adults based on the IAAO (6). The MOD diet represents the lower limit of the current recommended protein intake for endurance athletes by the American College of Sports Medicine (1) and a safe intake according to NBAL (4,5). The HIGH diet reflects the protein intake that was recently re-assessed using the novel IAAO tracer method as being sufficient to maximize whole body protein synthesis (12). ...
Recommendations for dietary protein are based primarily intakes that maintain nitrogen (i.e. protein) balance rather than optimize metabolism and/or performance.
Purpose:
To determine how varying protein intakes, including a new tracer-derived safe intake, alter whole body protein metabolism and exercise performance during training.
Methods:
Using a double-blind randomized crossover design, 10 male endurance-trained runners (age, 32±8 yr; VO2peak, 65.9±7.9 ml O2·kg·min) performed 3 trials consisting of 4 days of controlled training (20, 5, 10, 20 km·d, respectively) while consuming diets providing 0.94 (LOW), 1.20 (MOD), and 1.83 (HIGH) g protein·kg·d. Whole body protein synthesis (S), breakdown (B), and net balance (NB) were determined by oral [N]glycine on the first and last day of the 4-d controlled training period whereas exercise performance was determined from maximum voluntary isometric contraction (MVC), 5-km Time Trial (5kmTT), and countermovement jump Impulse (IMP) and peak force (PF) before and immediately after the 4-d intervention.
Results:
S and B were not affected by protein intake whereas NB showed a dose-response (HIGH > MOD > LOW, P<0.05) with only HIGH being in positive balance (P<0.05). There was a trend (P=0.06) towards an interaction in 5kmTT with HIGH having a moderate effect over LOW (ES=0.57) and small effect over MOD (ES = 0.26). IMP decreased with time (P<0.01) with no effect of protein (P=0.56). There was no effect of protein intake (P≥0.06) on MVC, IMP, or PF performance.
Conclusion:
Our data suggest that athletes who consume dietary protein towards the upper end of current ACSM recommendations (1.2-2 g·kg) would better maintain protein metabolism and potentially exercise performance during training.
... Higher-protein intakes are recommended for physically active adults who routinely participate in endurance exercise [7][8][9]. To date, no studies have investigated the impact of dietary protein intake on glucose homeostasis in endurance-trained adults. ...
... Actual macronutrient composition of the each diet was 48% carbohydrate (5.4 g kg -1 d -1 ), 26% fat, and 26% protein (3.1 g kg -1 d -1 ) for HP, 60% carbohydrate (7.4 g kg -1 d -1 ), 26% fat, and 14% protein (1.8 g kg -1 d -1 ) for MP, and 66% carbohydrate (8.3 g kg -1 d -1 ), 27% fat, and 7% protein (0.9 g kg -1 d -1 ) for LP. Extended details of the diet intervention have been previously reported [8]. Volunteers maintained their normal level of training throughout the study. ...
... The increased availability of carbohydrate with the consumption of lower dietary protein (i.e., RDA) contributes to higher rates of carbohydrate oxidation and a reduced need for hepatic glucose production. In contrast, when protein intake increased and approached the upper limit of the AMDR, a concomitant increase in protein oxidation should spare carbohydrate use as a fuel thereby reducing the need for endogenous glucose production [8]. Indeed, consistent with this proposed scenario, previously published data from this investigation showed greater carbohydrate and lower protein oxidation for the MP vs. HP diets and increased protein oxidation with increased protein consumption, which is consistent with the higher rate rates of glucose disposal observed for the MP diet [8,21]. ...
To examine the effects of higher-protein diets on endogenous glucose metabolism in healthy, physically active adults, glucose turnover was assessed in five endurance-trained men (age 21.3 ± 0.3 y, VO2peak 70.6 ± 0.1 mL kg-1 min-1) who consumed dietary protein intakes spanning the current dietary reference intakes.
Using a randomized, crossover design, volunteers consumed 4 week eucaloric diets providing either a low (0.8 g kg-1 d-1; LP), moderate (1.8 g kg-1 d-1; MP), or high (3.6 g kg-1 d-1; HP) level of dietary protein. Glucose turnover (Ra, glucose rate of appearance; and Rd glucose rate of disappearance) was assessed under fasted, resting conditions using primed, constant infusions of [6,6-2H2] glucose. Glucose Ra and Rd (mg kg-1 min-1) were higher for MP (2.8 ± 0.1 and 2.7 ± 0.1) compared to HP (2.4 ± 0.1 and 2.3 ± 0.2, P < 0.05) and LP (2.3 ± 0.1 and 2.2 ± 0.1, P < 0.01) diets. Glucose levels (mmol/L) were not different (P > 0.05) between LP (4.6 ± 0.1), MP (4.8 ± 0.1), and HP (4.7 ± 0.1) diets.
Level of protein consumption influenced resting glucose turnover in endurance athletes in a state of energy balance with a higher rate of turnover noted for a protein intake of 1.8 g kg-1 d-1. Findings suggest that consumption of protein in excess of the recommended dietary allowance but within the current acceptable macronutrient distribution range may contribute to the regulation of blood glucose when carbohydrate intake is reduced by serving as a gluconeogenic substrate in endurance-trained men.
... Many nutritional, physiological, and pathological processes can interfere with protein turnover in adult animals, including diet composition [7], resistance exercise or hypertrophy [8,9], a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 disease, and aging [10,11]. This process can induce changes in muscle mass, in turn, affecting health, physical activity, and disease resistance [10]. ...
Stable isotope methods have been used to study protein metabolism in humans; however, there application in dogs has not been frequently explored. The present study compared the methods of precursor (13C-Leucine), end-products (15N-Glycine), and amino acid oxidation (13C-Phenylalanine) to determine the whole-body protein turnover rate in senior dogs. Six dogs (12.7 ± 2.6 years age, 13.6 ± 0.6 kg bodyweight) received a dry food diet for maintenance and were subjected to all the above-mentioned methods in succession. To establish 13C and 15N kinetics, according to different methodologies blood plasma, urine, and expired air were collected using a specifically designed mask. The volume of CO2 was determined using respirometry. The study included four methods viz. 13C-Leucine, 13C-Phenylalanine evaluated with expired air, 13C-Phenylalanine evaluated with urine, and 15N-Glycine, with six dogs (repetitions) per method. Data was subjected to variance analysis and means were compared using the Tukey test (P<0.05). In addition, the agreement between the methods was evaluated using Pearson correlation and Bland-Altman statistics. Protein synthesis (3.39 ± 0.33 g.kg-0,75. d⁻¹), breakdown (3.26 ± 0.18 g.kg-0.75.d⁻¹), and flux estimations were similar among the four methods of study (P>0.05). However, only 13C-Leucine and 13C-Phenylalanine (expired air) presented an elevated Pearson correlation and concordance. This suggested that caution should be applied while comparing the results with the other methodologies.
... We have established additional exclusion criteria, not mentioned in these previous studies, such as presence of grade II obesity [body mass index (BMI) ≥ 35 kg/m 2 ], severe physical disability, and lactation. Moreover, blood levels of AAs could be influenced by other factors such as medication, diet, and exercise [34][35][36][37]. Our patients were taking pain-related medication and maintained their usual diet and physical activity but, unlike previous studies, we examined the effects of these factors on AA levels. ...
Fibromyalgia is a complex illness to diagnose and treat.
To evaluate a broad range of circulating free amino acid (AA) levels in fibromyalgia patients as well as the ability of the AAs to differentiate fibromyalgia patients from healthy subjects.
We carried out a case-control study to evaluate AA levels in 62 patients with fibromyalgia and 78 healthy subjects. This study adheres to the STROBE guidelines.
AAs content was assayed by HPLC in serum samples. The predictive value of AA levels in fibromyalgia was determined by receiver operating characteristic (ROC) curve and forward binary logistic regression analyses.
Fibromyalgia patients showed higher serum levels of aspartic acid, glutamic acid, aminoadipic acid, asparagine, histidine, 3-methyl-histidine, 5-methyl-histidine, glycine, threonine, taurine, tyrosine, valine, methionine, isoleucine, phenylalanine, leucine, ornithine, lysine, branched chain AAs (BCAAs), large neutral AAs, essential AAs (EAAs), non-essential AAs (NEAAs), basic AAs, EAAs/NEAAs ratio, phenylalanine/tyrosine ratio, and global arginine bioavailability ratio than the controls. Serum alanine levels were lower in patients than in controls. According to ROC analysis, most of these AAs may be good markers for differentiating individuals with fibromyalgia from healthy subjects. Results of logistic regression showed that the combination of glutamic acid, histidine, and alanine had the greatest predictive ability to diagnose fibromyalgia.
Our results show an imbalance in serum levels of most AAs in patients with fibromyalgia, which suggest a metabolic disturbance. The determination of serum levels of these AAs may aid in the diagnosis of fibromyalgia, in combination with clinical data of the patient.
... It is possible that the variations in dietary CP and ME among the dietary groups caused the higher creatinine level by increasing the muscle breakdown at the expense of muscle synthesis. The phenomenon could be attributed to the lower calorie/protein in the mentioned diets (Gaine et al., 2006).On the other hand, The high protein concentration typical of commercial diets used in the starter phase of broiler rearing results in a higher urea concentration content (Szabo et al., 2005). On the other hand, no significant effect in urea concentration was found by Rajman et al., (2006) in growing meat-type chickens and by Schmidt et al., (2007) in pheasants, additionally confirming the great variability in uric acid content in birds. ...
... There are several studies that have proved that vitamin D promotes calcium absorption in the body, which could promote bone growth and the maintenance of bone density and muscle strength [37,38]. As protein intake increases, amino acid availability increases and total protein oxidation increases; these are processes which may be related to better endurance performance [39]. ...
Background:
This study aims to investigate the associations between dietary patterns (breakfast, egg, dairy products, and sugared beverage intake frequencies) and physical fitness among Chinese children and adolescents in Shaanxi Province.
Methods:
Data were extracted from the Chinese National Survey on Students' Constitution and Health (CNSSCH). The study ultimately included 7305 participants (48.4% male, 51.6% female) aged 6-22 in Shaanxi Province, China. Multiple linear regression was used to examine the association of the frequency of breakfast, egg, dairy product, and sugared beverage intakes with physical fitness.
Results:
The frequency of breakfast, egg, and dairy product intakes were all independently and positively associated with the level of physical fitness. The frequency of sugared beverage intake was negatively associated with the level of physical fitness.
Conclusion:
Healthier dietary patterns (i.e., higher breakfast, egg, and dairy product intakes and lower sugared beverage intake) were associated with greater physical fitness. Specifically, maintaining a healthy dietary pattern of breakfast, egg, and dairy product intakes can positively affect the strength and endurance performance of children and adolescents. Increased dairy product intake plays a crucial part in boosting the physical fitness total scores of children and adolescents.
... In addition, the EAA leucine is well documented as a nutrient signal, or trigger, that stimulates muscle protein synthesis (Tessari et al., 2016). Our group has successfully implemented this approach to diet and exercise interventions to increase dietary leucine intake and support whole body and skeletal muscle protein synthesis (Bolster et al., 2005;Gaine et al., 2006;Pikosky et al., 2006;Pasiakos et al., 2010). Meat -a complete, high-quality protein source that is EAA and micronutrient dense-was incorporated into healthy eating patterns for habitual consumption throughout the various dietary intervention periods in these studies. ...
... It is possible that the variations in dietary CP and energy among the dietary groups caused the higher CK level by increasing the muscle breakdown at the expense of muscle synthesis. The phenomenon could be attributed to the lower calorie/protein in the mentioned diets, and consequently lower availability of energy under such energy demanding stressful condition (Fagan et al. 1992;Gaine et al. 2006). ...
The effects of feeding low dietary crude protein (CP) and/or metabolisable energy (ME) with or without supplemental protease on growth performance, carcase characteristics and physiological responses in broiler chickens were investigated under cyclic heat stress condition. A total of 350 day-old male broiler chicks were fed with one of the following seven experimental diets: (1) recommended-CP and recommended-ME (RPE, served as control); (2) recommended-CP and low-ME (RPLE); (3) recommended-CP and low-ME with protease (RPLEP); (4) low-CP and recommended-ME (LPRE); (5) low-CP and recommended-ME with protease (LPREP); (6) low-CP and low-ME (LPE) and (7) low-CP and low-ME with protease (LPEP). From 22 to 42 d of age, half of the chickens from each dietary group were exposed to 34 ± 1 °C for 7 h daily (heat stress), whereas the other half were raised at constant 23 ± 2 °C (normal temperature). Supplementation of protease to RPLE, LPRE and LPE diets had no significant effects on feed intake (FI), weight gain (WG) or feed conversion ratio (FCR). Diet had no effect on serum glucose, total protein, certain acute phase proteins (APPs), corticosterone or breast yield. Regardless of protease supplementation, heat stressed birds had significantly lower FI, WG and breast yield, and higher FCR, APPs and corticosterone compared to birds raised in normal temperature. In conclusion, dietary supplementation of protease to low CP and/or ME diets showed negligible effects on growth performance, carcase characteristic and physiological responses in broiler chickens under heat stress condition. The inclusion of microbial protease in broiler diets could be considered by poultry industry as an effective nutritional tool for reducing ME or CP, in order to decrease abdominal fat deposition, improve feed efficiency and increase the profit margin.
HIGHLIGHTS
• Protease supplementation has no specific help for broilers under heat stress.
• Feeding low CP and/or ME diet is not stressful for broiler chickens.
... In the case of endurance athletes, the specific recommended protein intake was set as 1.2−1.4 g·kg −1 ·day −1 [17,46], largely based on the research examining the protein intakes required to achieve NBAL [28,47,48]. The population-safe protein intake in the current study was higher than that in previous studies [28,47]. ...
A higher protein intake is recommended for athletes compared to healthy non-exercising individuals. Additionally, the distribution and quality (i.e., leucine content) of the proteins consumed throughout the day should be optimized. This study aimed to determine the nitrogen balance and distribution of protein and amino acid intakes in competitive swimmers during the general preparation phase. Thirteen swimmers (age: 19.7 ± 1.0 years; VO2max: 63.9 ± 3.7 mL·kg−1·min−1, mean ± standard deviation) participated in a five-day experimental training period. Nutrient intakes were assessed using dietary records. Nitrogen balance was calculated from the daily protein intake and urinary nitrogen excretion. The intake amounts of amino acids and protein at seven eating occasions were determined. The average and population-safe intakes for zero nitrogen balance were estimated at 1.43 and 1.92 g·kg−1·day−1, respectively. The intake amounts of protein and leucine at breakfast, lunch, and dinner satisfied current guidelines for the maximization of muscle protein synthesis, but not in the other four occasions. The population-safe protein intake level in competitive swimmers was in the upper range (i.e., 1.2–2.0 g·kg−1·day−1) of the current recommendations for athletes. The protein intake distribution and quality throughout the day may be suboptimal for the maximization of the skeletal muscle adaptive response to training.
... gIkg j1 Id j1 (32). Energy balance, or the consumption of adequate calories, particularly carbohydrates, to meet those expended, is important to protein metabolism so that amino acids are spared for protein synthesis and not oxidized to assist in meeting energy needs (33,34). In addition, discussion continues as to whether sex differences in protein-related metabolic responses to exercise exist (35,36). ...
... 24 h −1 during a training season [105]. Additional investigations on whole body protein turnover [106] and skeletal muscle fractional synthetic rates in trained endurance humans [107] suggest that a protein intake of 1.2 g protein −1 . 24 h −1 (or 10-12% of total energy) should achieve a positive nitrogen balance. ...
Muscle mass is the major deposit of protein molecules with dynamic turnover between net protein synthesis and degradation. In human subjects, invasive and non-invasive techniques have been applied to determine their skeletal muscle catabolism of amino acids at rest, during and after different forms of physical exercise and training. The aim of this review is to analyse the turnover flux and the relative oxidation rate of different types of muscle proteins after one bout of exercise as well as after resistance and endurance condition of training. Protein feeding in athletes appears to be a crucial nutrition necessity to promote the maintenance of muscle mass and its adaptation to the need imposed by the imposed technical requirements. In resting human individuals, the recommended protein daily allowance is about 0.8 g (dry weight) kg−1 body weight per 24 h knowing that humans are unable to accumulate protein stores in muscle tissues. Nevertheless, practical feeding recommendations related to regular exercise practice are proposed to athletes by different bodies in order to foster their skills and performance. This review will examine the results obtained under endurance and resistance type of exercise while consuming single or repeated doses of various ingestions of protein products (full meat, essential amino acids, specific amino acids and derivatives, vegetarian food). From the scientific literature, it appears that healthy athletes (and heavy workers) should have a common diet of 1.25 g kg−1 24 h to compensate the exercise training muscle protein degradation and their resynthesis within the following hours. A nitrogen-balance assay would be recommended to avoid any excessive intake of protein. Eventually, a daily equilibrated food intake would be of primer importance versus inadequate absorption of some specific by-products.
... There are other concomitant factors such as timing intake in relation to training, energy balance, carbohydrates availability and amino acids composition of ingested proteins that must be considered. All these factors have a key role for the use of dietary amino acids in protein synthesis, avoiding their oxidation to meet energy requirements [20,21]. Moreover, protein metabolism during and after exercise is also affected by sex, age and the intensity, duration and type of training [1,16]. ...
... However, 25.8% Tunisian youth weightlifters exceed the value of 2.4g/kg ̵ ¹. Gaine's study demonstrated clearly that from this value the anabolic response capped while the degradation of amino acids increases significantly, this may negatively impact the progression of muscle development [21]. Other studies on animals suggest that excessive protein intake raises the rate of myostatin, which decreases the rate of growth hormone [22]. ...
Aim:
to study the quantitative and qualitative aspects of daily spontaneous nutrition as well as anthropometric characteristics and body composition of young Tunisian weightlifters.
Methods:
Thirty one boys aged between 14 and 18 years, practicing for two hours a day, six days a week in the four weightlifting clubs in Tunis were invited to attend an evaluation session for a food survey (3 days recall, with consumption frequency over a period of 7 days) and the assessment of anthropometric measurements (Weight, height and skinfolds).
Results:
Energy intake was acceptable. However, an imbalance nutrient intake was revealed. Concerning macronutrient, fat and protein were above the recommended allowances (p<0.01). Further, the percentage of saturated fatty acids was significantly above the recommended values while the percentages of polyunsaturated fatty acids and monounsaturated fatty acids were restricted. Regarding the micronutrient, the intake of calcium, magnesium and potassium were restrictive (p<0.01). As for the fluid intake, a limited contribution was observed (p<0.01). Several correlations between body composition and dietary intake have been found.
Conclusion:
Nutritional education may lead these young weightlifters to adopt appropriate nutritional habits to optimize dietary intake. This fact could be compromising of a more suitable body composition and could have a positive bearing on athletic performance.
... Thus, the protein requirements of endurance-trained subjects in only the resting condition are not fully understood. To our best knowledge, only a single former study reported that a protein intake of 1.2 g Á kg 21 Á d 21 was required to achieve zero nitrogen balance in trained subjects at rest (56), which is higher than the protein requirements of healthy adults (57). However, some investigators have suggested that the efficiency of protein utilization increases after chronic exercise training (58)(59)(60)(61). ...
Background:
The indicator amino acid oxidation (IAAO) method has contributed to establishing protein and amino acid (AA) requirements by determining the optimal protein and AA intake that maximizes whole-body protein synthesis. However, it has not been used with endurance-trained subjects.
Objective:
This study aimed to determine the optimal AA intake immediately after endurance exercise and at rest in endurance-trained rats by using the IAAO method.
Methods:
Four-week-old male Fischer rats were divided into a sedentary (SED) group and a trained (TR) group, which underwent treadmill training 5 d/wk for 6 wk at 26 m/min for 60 min/d. On the metabolic trial day, half of the TR group was provided with test diets after daily treadmill running (TR-PostEx). The other half of the TR group (TR-Rest) and all of the SED group were provided with test diets while at rest. The test diets contained different amounts of AAs (3.3-37.3 g ⋅ kg(-1) ⋅ d(-1)). Phenylalanine in the test diet was replaced with L-[1-(13)C]phenylalanine. The phenylalanine oxidation rate (PheOx) was determined with (13)CO2 enrichment in breath, CO2 excretion rate, and enrichment of phenylalanine in blood during the feeding period. The optimal AA intake was determined with biphasic mixed linear regression crossover analysis for PheOx, which identified a breakpoint at the minimal PheOx in response to graded amounts of AA intake.
Results:
The optimal AA intake in the TR-PostEx group (26.8 g ⋅ kg(-1) ⋅ d(-1); 95% CI: 21.5, 32.1 g ⋅ kg(-1) ⋅ d(-1)) was significantly higher than in the SED (15.1 g ⋅ kg(-1) ⋅ d(-1); 95% CI: 11.1, 19.1 g ⋅ kg(-1) ⋅ d(-1)) and TR-Rest (13.3 g ⋅ kg(-1) ⋅ d(-1); 95% CI: 10.9, 15.7 g ⋅ kg(-1) ⋅ d(-1)) groups, which did not differ.
Conclusions:
Greater AA intake is required to maximize whole-body protein synthesis immediately after endurance exercise than at rest, but not at rest in endurance-trained rats.
... Adult athletes who engage in both aerobic endurance and resistance-based exercise have been estimated to require more protein than sedentary controls (2), with elite endurance athletes requiring intakes nearly twice as high (1.6-1.7 g·kg -1 ·day -1 [9]) as their sedentary counterparts. Even individuals who are only modestly trained in endurance sports appear to require protein intakes that are higher (1.2-1.4 g·kg -1 ·d -1 ) than the general population (17). Limited data are emerging on the relationship between protein intakes and exercise in youth. ...
Current Dietary Reference Intakes (DRI) for protein for children and youth require revision as they were derived primarily on nitrogen balance data in young children or extrapolated from adult values; did not account for the possible influence of above average physical activity; and did not set an upper tolerable level of intake. Revision of the protein DRIs requires new research that investigates: 1) long-term dose-response to identify protein and essential amino acid requirements of both sexes at various pubertal stages and under differing conditions of physical activity; 2) the acute protein needs (quantity and timing) following a single bout of exercise; 3) the potential adverse effects of chronic high intakes of protein; and 4) new measurement techniques (i.e., IAAO or stable isotope methodologies) to improve accuracy of protein needs. While active individuals may require protein in excess of current DRIs, most active Canadian children and youth have habitual protein intakes that exceed current recommendations.
... There are other concomitant factors such as timing intake in relation to training, energy balance, carbohydrates availability and amino acids composition of ingested proteins that must be considered. All these factors have a key role for the use of dietary amino acids in protein synthesis, avoiding their oxidation to meet energy requirements [20,21]. Moreover, protein metabolism during and after exercise is also affected by sex, age and the intensity, duration and type of training [1,16]. ...
... Multi-nutrient insufficiency and 1C metabolism P Katre et al restriction of protein in healthy humans has been shown to cause a decrease in whole body proteolysis as measured by the rate of appearance of leucine and a decrease in the rate of oxidation of leucine/protein 27,28 and cause a decrease in the rate of oxidation of leucine in the rat. 29 These changes in essential amino acids were associated with a small increase in the levels of glycine and serine in the plasma. ...
Background/objectives:
Multi-nutrient insufficiencies as a consequence of nutritional and economic factors are common in India and other developing countries. We have examined the impact of multi-nutrient insufficiency on markers of one carbon (1C) metabolism in the blood, and response to a methionine load in clinically healthy young women.
Subjects/methods:
Young women from Pune, India (n=10) and Cleveland, USA (n=13) were studied. Blood samples were obtained in the basal state and following an oral methionine load (50 mg/kg of body weight in orange juice). Plasma concentrations of vitamin B12, folate and B6 were measured in the basal state. The effect of methionine load on the levels of methionine, total homocysteine, cysteine, glutathione and amino acids was examined.
Results:
Indian women were significantly shorter and lighter compared with the American women and had lower plasma concentration of vitamins B12, folate and B6, essential amino acids and glutathione, but higher concentration of total homocysteine. The homocysteine response to methionine load was higher in Indian women. The plasma concentrations of glycine and serine increased in the Indian women after methionine (in juice) load. A significant negative correlation between plasma B6 and homocysteine (r= -0.70), and plasma folate and glycine and serine levels were observed in the Indian group (P<0.05) but not in the American group.
Conclusions:
Multi-nutrient insufficiency in the Indian women caused unique changes in markers of whole body protein and 1C metabolism. These data would be useful in developing nutrient intervention strategies.European Journal of Clinical Nutrition advance online publication, 16 September 2015; doi:10.1038/ejcn.2015.155.
... A significant protein intake ranging between 1.2 to 1.7 g/kg BM per day is required for optimal health and performance of endurance athletes [2]. Studies examining protein intake in athletes have shown an increased requirement for protein in endurance trained athletes345 as opposed to healthy adult males (i.e., 0.8 g/kg) due to increased amino acid oxidation during exercise and for growth and repair of muscle tissue [6]. Maintenance of normal body water during strenuous training and minimising the level of dehydration (i.e., preventing a BM loss of > 2%) during endurance exercise achieved by consuming fluids at a rate of 0.4 to 0.8 L/h ad libitum is now recommended [7]. ...
... At present, the evidence is strong that protein in excess of about 25 to 30g at one meal or snack is "oxidized"/used as fuel, rather than for protein synthesis. 38 Although protein is required for optimal muscle growth and strength gains, all data indi cate that a protein intake of 0.9g/lb of body weight each day (180g for a 200lb person) is more than adequate for even the most serious weightlifter or bodybuilder, as long as the diet provides sufficient energy. Importantly, even in the face of an energy deficit, consuming a high protein diet does not mitigate any stressinduced decre ments in anabolic hormones. ...
The US Special Operations Command requires sound recommendations on nutrition to ensure optimal performance of Special Operations personnel. New information continues to emerge, and previous recommendations need to be modified as the evidence base continues to grow. The first 10 Commandments of Nutrition were published in the SEAL professional journal Full Mission Profile in 1992, published for the second time in this journal in 2005, and now revised a second time to reflect the newest science. Whether you are part of the Special Operations Forces (SOF) community or an athlete seeking to improve your performance, these are simple and helpful nutrition guidelines to follow.
... [22,27,28] From physiological studies it is known that dietary protein content has a regulatory effect on protein synthesis and degradation, [29,30] e.g. increased protein intake significantly increases the rate of whole body protein turnover, [31][32][33] and hence the renal hemodynamics, including glomerular filtration rates. [34] On the level of organs and excreta, an effect of dietary protein content on isotopic nitrogen turnover was found in blood of bats and birds. ...
Isotopic turnover quantifies the metabolic renewal process of elements in organs and excreta. Knowledge of the isotopic turnover of animal organs and excreta is necessary for diet reconstruction via stable isotope analysis, as used in animal ecology, palaeontology and food authentication. Effects of dietary protein content on the isotopic carbon and nitrogen turnover (i.e. delay, representing the time between ingestion and start of renewal, and half-life) are unknown for most mammalian organs and excreta.
To examine the effect of dietary protein content on turnover (delay and turnover rate), we fed 18 rats either a diet at protein maintenance or above protein maintenance, and quantified their isotopic carbon and nitrogen turnover in ten organs and excreta. These included the excreta faeces and urine, the visceral organs blood plasma, liver, kidney, lung and spleen, the cerebral tissue brain, and the muscular tissues heart and muscle. For data analysis, we used piecewise linear/non-linear exponential modelling that allows quantifying delay and turnover rate simultaneously.
Delays were ~0.5 days for carbon and nitrogen turnover and were not affected by dietary protein content. Half-lives during the following reaction progress were in the range of 1 to 45 days, increasing from excreta to visceral organs to muscular and cerebral organs. Rats fed the higher protein amount had 30% shorter nitrogen half-lives, and 20% shorter carbon half-lives.
The renewal times of organs and excreta depend on the dietary protein content. Hence, isotopic diet reconstruction is confronted with variation in half-lives within the same organ or excrement, altering the time window through which information can be perceived. Copyright © 2013 John Wiley & Sons, Ltd.
... 4 Increasing dietary protein intake upregulates whole-body protein turnover and improves net protein utilization during energy balance. 5 Therefore, consuming dietary protein at levels exceeding the recommended dietary allowance (RDA, 40.8 g kg À 1 per day) may offset energy deficit-induced downregulations in whole-body protein turnover. Numerous studies in overweight and obese adults have demonstrated protein conservation secondary to energy deficit, and suggest a whole-body protein metabolic advantage through the consumption of dietary protein at levels approaching two times the RDA. ...
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.
... A significant protein intake ranging between 1.2 to 1.7 g/kg BM per day is required for optimal health and performance of endurance athletes [2]. Studies examining protein intake in athletes have shown an increased requirement for protein in endurance trained athletes [3][4][5] as opposed to healthy adult males (i.e., 0.8 g/kg) due to increased amino acid oxidation during exercise and for growth and repair of muscle tissue [6]. Maintenance of normal body water during strenuous training and minimising the level of dehydration (i.e., preventing a BM loss of > 2%) during endurance exercise achieved by consuming fluids at a rate of 0.4 to 0.8 L/h ad libitum is now recommended [7]. ...
Background: Explanations for the phenomenal success of East African distance runners include unique dietary practices. The aim of the present study was to assess the food and macronutrient intake of elite Ethiopian distance runners during a period of high intensity exercise training at altitude and prior to major competition.
... The increased kinetics indicates increased breakdown after the 6-day cycle tour, which could be explained by the energy deficit across the 6 days. Protein intake in this study (mean 2.9 g × kg (1 ) was well above the recommended amount for endurance athletes and previous studies have reported that the level of dietary protein has an influence on whole-body protein turnover, with increasing intake resulting in an increased rate of whole-body protein breakdown and oxidation (Gaine et al., 2006(Gaine et al., , 2007. The increased protein intake over the 6 days of the tour in this study may have been a cause of the increased protein breakdown for participant 1, but other physiological changes may in fact have been responsible (see discussion below). ...
Marked energy expenditure, independent of energy balance, could change whole-body protein turnover. The aims of the present study were to determine the effect of participation in a 6-day, 10-stage cycling stage tour on whole-body protein turnover in elite male cyclists, and to determine whether energy and protein turnover are related to fatigue and over-reaching. C-leucine was used to determine 18-h whole-body protein turnover in cyclists both before and immediately after a cycling stage race. The 18-h period included two feeding periods to simulate a normal evening meal and a normal breakfast meal, and two fasted periods including overnight. Blood was drawn for the determination of plasma cortisol and serum ferritin on days 2, 4, and 6 and a Profile of Mood States questionnaire was administered on alternate days during the tour event for determination of markers of over-reaching. Mean leucine rate of appearance was unchanged from pre- to post-tour during both fed and fasted conditions and mean energy balance was maintained. Serum ferritin concentration declined and plasma cortisol concentration remained stable over the 6 days. Markers of overtraining were evident in one athlete who pulled out of the tour event due to fatigue on the second to last day. Our main finding was that high energy output over a 6-day period did not significantly change protein turnover during fed, fasted or overnight conditions.
... Our results indicate that the change in leucine oxidation from the fasted to fed states at the highest protein intake was negatively correlated with nitrogen balance-based estimates of protein requirement (Fig. 6). This finding supports the notion that protein oxidation increases at protein intakes that exceed dietary need and provides evidence for a qualitative link between nitrogen and isotope-labeled amino acid based assessments of protein requirement as previously reported [19,37,55]. This notion is also supported by the positive correlation observed between the change in leucine oxidation from the fasted to fed states and nitrogen balance across all protein intakes (Fig. 5) and is in line with previous reports [56,57]. ...
... In one study on young gymnasts, using both NBal and the 15 N-glycine technique, we were able to observe a positive net protein balance (+ 0.61 g protein/24 h) with a mean protein intake of over 1.39 g protein/24 h during a training season (76). Additional investigations on whole-body protein turnover (77) and skeletal muscle fractional synthetic rates in trained endurance humans (78) suggest that a protein intake of 1.2 g/24 h (or 10-12% of total energy) should achieve a positive NBal. A recent survey by Slater and Phillips (79) reported a protein intake that ranged from 1.1 to 3.3 g/24 h among adult male strength and power athletes during their training. ...
Skeletal muscle is the major deposit of protein molecules. As for any cell or tissue, total muscle protein reflects a dynamic turnover between net protein synthesis and degradation. Noninvasive and invasive techniques have been applied to determine amino acid catabolism and muscle protein building at rest, during exercise and during the recovery period after a single experiment or training sessions. Stable isotopic tracers (13C-lysine, 15N-glycine, ²H5-phenylalanine) and arteriovenous differences have been used in studies of skeletal muscle and collagen tissues under resting and exercise conditions. There are different fractional synthesis rates in skeletal muscle and tendon tissues, but there is no major difference between collagen and myofibrillar protein synthesis. Strenuous exercise provokes increased proteolysis and decreased protein synthesis, the opposite occurring during the recovery period. Individuals who exercise respond differently when resistance and endurance types of contractions are compared. Endurance exercise induces a greater oxidative capacity (enzymes) compared to resistance exercise, which induces fiber hypertrophy (myofibrils). Nitrogen balance (difference between protein intake and protein degradation) for athletes is usually balanced when the intake of protein reaches 1.2 g·kg-1·day-1 compared to 0.8 g·kg-1·day-1 in resting individuals. Muscular activities promote a cascade of signals leading to the stimulation of eukaryotic initiation of myofibrillar protein synthesis. As suggested in several publications, a bolus of 15-20 g protein (from skimmed milk or whey proteins) and carbohydrate (± 30 g maltodextrine) drinks is needed immediately after stopping exercise to stimulate muscle protein and tendon collagen turnover within 1 h.
... A significant protein intake ranging between 1.2 to 1.7 g/kg BM per day is required for optimal health and performance of endurance athletes [2]. Studies examining protein intake in athletes have shown an increased requirement for protein in endurance trained athletes [3][4][5] as opposed to healthy adult males (i.e., 0.8 g/kg) due to increased amino acid oxidation during exercise and for growth and repair of muscle tissue [6]. Maintenance of normal body water during strenuous training and minimising the level of dehydration (i.e., preventing a BM loss of > 2%) during endurance exercise achieved by consuming fluids at a rate of 0.4 to 0.8 L/h ad libitum is now recommended [7]. ...
Explanations for the phenomenal success of East African distance runners include unique dietary practices. The aim of the present study was to assess the food and macronutrient intake of elite Ethiopian distance runners during a period of high intensity exercise training at altitude and prior to major competition.
The dietary intake of 10 highly-trained Ethiopian long distance runners, living and training at high altitude (approximately 2400 m above sea level) was assessed during a 7 day period of intense training prior to competition using the standard weighed intake method. Training was also assessed using an activity/training diary.
Body mass was stable (i.e., was well maintained) over the assessment period (pre: 56.7 ± 4.3 kg vs. post: 56.6 ± 4.2 kg, P = 0.54; mean ± SD). The diet comprised of 13375 ± 1378 kJ and was high in carbohydrate (64.3 ± 2.6%, 545 ± 49 g, 9.7 ± 0.9 g/kg). Fat and protein intake was 23.3 ± 2.1% (83 ± 14 g) and 12.4 ± 0.6% (99 ± 13 g, 1.8 ± 0.2 g/kg), respectively. Fluid intake comprised mainly of water (1751 ± 583 mL), while no fluids were consumed before or during training with only modest amounts being consumed following training.
Similar to previous studies in elite Kenyan distance runners, the diet of these elite Ethiopian distance runners met most recommendations of endurance athletes for macronutrient intake but not for fluid intake.
... Whole-body protein synthesis is affected not only by protein intake but by exercise as well, especially in the period after exercise (44). The higher protein turnover is suggested to increase the protein requirement for maintenance of nitrogen balance (27). In practice, exercise induces an increase in food intake and thus protein intake remains sufficient when it comprises a minimum of 10% of energy intake. ...
The role of dietary protein in weight loss and weight maintenance encompasses influences on crucial targets for body weight regulation, namely satiety, thermogenesis, energy efficiency, and body composition. Protein-induced satiety may be mainly due to oxidation of amino acids fed in excess, especially in diets with "incomplete" proteins. Protein-induced energy expenditure may be due to protein and urea synthesis and to gluconeogenesis; "complete" proteins having all essential amino acids show larger increases in energy expenditure than do lower-quality proteins. With respect to adverse effects, no protein-induced effects are observed on net bone balance or on calcium balance in young adults and elderly persons. Dietary protein even increases bone mineral mass and reduces incidence of osteoporotic fracture. During weight loss, nitrogen intake positively affects calcium balance and consequent preservation of bone mineral content. Sulphur-containing amino acids cause a blood pressure-raising effect by loss of nephron mass. Subjects with obesity, metabolic syndrome, and type 2 diabetes are particularly susceptible groups. This review provides an overview of how sustaining absolute protein intake affects metabolic targets for weight loss and weight maintenance during negative energy balance, i.e., sustaining satiety and energy expenditure and sparing fat-free mass, resulting in energy inefficiency. However, the long-term relationship between net protein synthesis and sparing fat-free mass remains to be elucidated.
... gIkg j1 Id j1 (32). Energy balance, or the consumption of adequate calories, particularly carbohydrates, to meet those expended, is important to protein metabolism so that amino acids are spared for protein synthesis and not oxidized to assist in meeting energy needs (33,34). In addition, discussion continues as to whether sex differences in protein-related metabolic responses to exercise exist (35,36). ...
It is the position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition. These organizations recommend appropriate selection of foods and fluids, timing of intake, and supplement choices for optimal health and exercise performance. This updated position paper couples a rigorous, systematic, evidence-based analysis of nutrition and performance-specific literature with current scientific data related to energy needs, assessment of body composition, strategies for weight change, nutrient and fluid needs, special nutrient needs during training and competition, the use of supplements and ergogenic aids, nutrition recommendations for vegetarian athletes, and the roles and responsibilities of sports dietitians. Energy and macronutrient needs, especially carbohydrate and protein, must be met during times of high physical activity to maintain body weight, replenish glycogen stores, and provide adequate protein to build and repair tissue. Fat intake should be sufficient to provide the essential fatty acids and fat-soluble vitamins, as well as contribute energy for weight maintenance. Although exercise performance can be affected by body weight and composition, these physical measures should not be a criterion for sports performance and daily weigh-ins are discouraged. Adequate food and fluid should be consumed before, during, and after exercise to help maintain blood glucose concentration during exercise, maximize exercise performance, and improve recovery time. Athletes should be well hydrated before exercise and drink enough fluid during and after exercise to balance fluid losses. Sports beverages containing carbohydrates and electrolytes may be consumed before, during, and after exercise to help maintain blood glucose concentration, provide fuel for muscles, and decrease risk of dehydration and hyponatremia. Vitamin and mineral supplements are not needed if adequate energy to maintain body weight is consumed from a variety of foods. However, athletes who restrict energy intake, use severe weight-loss practices, eliminate one or more food groups from their diet, or consume unbalanced diets with low micronutrient density, may require supplements. Because regulations specific to nutritional ergogenic aids are poorly enforced, they should be used with caution, and only after careful product evaluation for safety, efficacy, potency, and legality. A qualified sports dietitian and in particular in the United States, a Board Certified Specialist in Sports Dietetics, should provide individualized nutrition direction and advice subsequent to a comprehensive nutrition assessment.
... gIkg j1 Id j1 (32). Energy balance, or the consumption of adequate calories, particularly carbohydrates, to meet those expended, is important to protein metabolism so that amino acids are spared for protein synthesis and not oxidized to assist in meeting energy needs (33,34). In addition, discussion continues as to whether sex differences in protein-related metabolic responses to exercise exist (35,36). ...
It is the position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition. These organizations recommend appropriate selection of foods and fluids, timing of intake, and supplement choices for optimal health and exercise performance. This updated position paper couples a rigorous, systematic, evidence-based analysis of nutrition and performance-specific literature with current scientific data related to energy needs, assessment of body composition, strategies for weight change, nutrient and fluid needs, special nutrient needs during training and competition, the use of supplements and ergogenic aids, nutrition recommendations for vegetarian athletes, and the roles and responsibilities of the sports dietitian. Energy and macronutrient needs, especially carbohydrate and protein, must be met during times of high physical activity to maintain body weight, replenish glycogen stores, and provide adequate protein to build and repair tissue. Fat intake should be sufficient to provide the essential fatty acids and fat-soluble vitamins and to contribute energy for weight maintenance. Although exercise performance can be affected by body weight and composition, these physical measures should not be a criterion for sports performance and daily weigh-ins are discouraged. Adequate food and fluid should be consumed before, during, and after exercise to help maintain blood glucose concentration during exercise, maximize exercise performance, and improve recovery time. Athletes should be well hydrated before exercise and drink enough fluid during and after exercise to balance fluid losses. Sports beverages containing carbohydrates and electrolytes may be consumed before, during, and after exercise to help maintain blood glucose concentration, provide fuel for muscles, and decrease risk of dehydration and hyponatremia. Vitamin and mineral supplements are not needed if adequate energy to maintain body weight is consumed from a variety of foods. However, athletes who restrict energy intake, use severe weight-loss practices, eliminate one or more food groups from their diet, or consume unbalanced diets with low micronutrient density may require supplements. Because regulations specific to nutritional ergogenic aids are poorly enforced, they should be used with caution and only after careful product evaluation for safety, efficacy, potency, and legality. A qualified sports dietitian and, in particular, the Board Certified Specialist in Sports Dietetics in the United States, should provide individualized nutrition direction and advice after a comprehensive nutrition assessment.
... 0.44 g protein kg ¡1 day ¡1 ) per g of dietary protein kg ¡1 day ¡1 . Such an eYciency (0.44) is lower than 0.59 reported in 12.7-year-old children (Gattas et al. 1992) but similar to 0.47 reported in adults (DRI 2005) and to the value (0.40) calculated in endurance trained young men (Gaine et al. 2006). With the increase in energy balance there was an increase of 0.88 mg N per 1 kJ kg EBW ¡1 day ¡1 (corresponding to 0.092 kJ if we assume that it is body proteins). ...
Few investigations have studied protein metabolism in children and adolescent athletes which makes difficult the assessment of daily recommended dietary protein allowances in this population. The problematic in paediatric competitors is the determination of additional protein needs resulting from intensive physical training. The aim of this investigation was to determine protein requirement in 14-year-old male adolescent soccer players. Healthy male adolescent soccer players (N = 11, 13.8 +/- 0.1 year) participated in a short term repeated nitrogen balance study. Diets were designed to provide proteins at three levels: 1.4, 1.2 and 1.0 g protein per kg body weight (BW). Nutrient and energy intakes were assessed from 4 day food records corresponding to 4 day training periods during 3 weeks. Urine was collected during four consecutive days and analysed for nitrogen. The nitrogen balances were calculated from mean daily protein intake, mean urinary nitrogen excretion and estimated faecal and integumental nitrogen losses. Nitrogen balance increased with both protein intake and energy balance. At energy equilibrium, the daily protein intake needed to balance nitrogen losses was 1.04 g kg(-1) day(-1). This corresponds to an estimated average requirement (EAR) for protein of 1.20 g kg(-1) day(-1) and a recommended daily allowance (RDA) of 1.40 g kg(-1) day(-1) assuming a daily nitrogen deposition of 11 mg kg(-1). The results of the present study suggest that the protein requirements of 14-year-old male athletes are above the RDA for non-active male adolescents.
The high GFR in vertebrates obligates large energy expenditure. Homer Smith's teleologic argument that this high GFR was needed to excrete water as vertebrates evolved in dilute seas is outdated. The GFR is proportional to the metabolic rate among vertebrate species and higher in warm-blooded mammals and birds than in cold-blooded fish, amphibians, and reptiles. The kidney clearance of some solutes is raised above the GFR by tubular secretion, and we presume secretion evolved to eliminate particularly toxic compounds. In this regard, high GFRs may provide a fluid stream into which toxic solutes can be readily secreted. Alternatively, the high GFR may be required to clear solutes that are too large or too varied to be secreted, especially bioactive small proteins and peptides. These considerations have potentially important implications for the understanding and treatment of kidney failure.
Background:
Assessment of whole body protein turnover (WBPT) can provide fundamental information about protein kinetics which underpins the conservation of lean tissue. Reliability and methodology studies on the measurement of WBPT are scarce. This study aimed to assess the effects of urine collection duration (9 versus 12 h) and the reproducibility of WBPT with the end product method calculated from ammonia as the end product.
Methods:
WBPT was assessed in 21 healthy participants (11 M, 10F) on 2 test days. WBPT was assessed using the end product method with a single dose of 15N glycine with ammonia as end product in a postprandial state with 9 and 12-h urine collections.
Results:
The CV for protein flux averaged 10% and 12% for 9 and 12-h urine collections respectively. Protein flux, synthesis and balance were significantly higher and protein breakdown significantly lower with 9-h urine collections compared to 12-h collections (P < 0.01) and there was a trend towards increasingly greater overestimation of 9-h calculated WBPT kinetics with greater overall rates of WBPT. Correlations between the 9 and 12-h values were strong (r > 0.962, P < 0.001 for all variables).
Conclusions:
The reproducibility of WBPT with ammonia as the end product was similar to previously reported reproducibility of the gold standard precursor technique. The use of a 12-h urine collection is more effective to achieve full turnover of the ammonia free amino acid (AA) pool.
Energy and protein metabolism are closely linked and substantially influence each other. Therefore, the combined measurement of protein and energy metabolism is a logical approach. There are several methods available for measurement of energy expenditure and of protein turnover that usually can be applied simultaneously without affecting either measurement. For energy expenditure, indirect calorimetry is the most accurate and most commonly applied method, but other methods like the doubly labelled water technique or the bicarbonate recovery method have also been applied in conjunction with measurement of protein turnover. For determination of protein turnover, isotope dilution methods are generally used. The precursor method relies on the measurement of the rate of appearance of an amino acid to be metabolized, while the end product method measures the amount of tracer appearing in urea and/or ammonia. The flooding dose technique depends on the ratio of the isotope enrichment in tissues to that in plasma. Each of these methods has distinct advantages and disadvantages that include: the accuracy and precision of results, complexity and necessary skills for application, cost, and applicability in laboratory or field. Thus, the choice of method for energy and protein metabolic measurements depends firstly on the research questions, and secondly on the equipment, expertise and funds available. The preferred method for measurement of energy expenditure is indirect calorimetry, which should be combined with the end product method for determination of protein turnover. The best tracer for measurement of protein turnover is carboxyl-C labelled leucine, unless for the indicator amino acid oxidation technique, for which carboxyl-C labelled phenylalanine is preferred. If indirect calorimetry cannot be performed, the doubly labelled water technique is recommended. If determination of CO2 production is not possible, the precursor method with 15N labelled amino acids, usually glycine, is a viable alternative. However, different methods to determine energy expenditure or different tracers should be considered for research questions that make the recommended approach impractical or inappropriate. The combined measurement of protein turnover and energy expenditure is especially useful for studies in humans and large mammals where the recruitment of subjects may be difficult. The main applications have been determination of energy cost of protein synthesis under a variety of conditions. The research objectives were mainly the study of the effects of health and disease on protein and energy metabolism, assessment of intervention strategies and maximisation of production efficiency in animals. Because of the close linkage of protein and energy metabolism, their simultaneous study can provide additional insights either method alone cannot offer.
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.
Both sportsmen and non-sportsmen usually make the same nutritional errors. Experience with sportsmen has shown that patterns of activity and nutrition do not always change in parallel. Only someone who feeds himself properly can expect his body to perform at a high level. If a sportsman is to achieve satisfactory energy balance, the composition of the nutrients and the quality of macronutrients (such as carbohydrates, fats, proteins and vitamins) are of decisive importance. This guarantees both the necessary nutritional density and the supply of nutrients thought - for physiological or biochemical reasons - to be related to physical performance in sport. If the links between nutrient deficiencies and restrictions in physical performance are born in mind, specific nutritional advice can be used to change sportsmen's nutritional habits and thus to improve their performance. This is ethically acceptable and may even improve their health.
Amino acids are necessary for skeletal muscle protein synthesis. The amount of dietary protein consumption needed to obtain these amino acids and optimize muscle hypertrophy has long been debated. Emerging research has provided us knowledge about the types of amino acids needed, the amounts, and when the best time is to consume them. Protein consumed before and after exercise can offset muscle protein breakdown but amounts higher than 5-15 grams will probably not drive further muscle hypertrophy. Protein intake at levels above 1.4g/(kg*day) will not likely result in further muscle hypertrophy. Overall protein intake does play a role in body composition, immune function and satiety.
Physical activity increases the rate of energy expenditure and, as a result, athletes have greater daily requirements of the three energy macronutrients, in particular carbohydrates and protein, when compared with sedentary individuals. There is ample research investigating adequate nutrient intake recommendations for athletes of various types, where differences occur with the modality, intensity, duration of exercise, and even gender. Understanding optimal nutrient composition is important for athletes and coaches because of the impact diet can play on nutrient utilization during exercise as well as in recovery from exercise. Effective manipulation of these requirements can facilitate and optimize training adaptations while also preventing untoward physiological changes from consuming either too much or too little of the macronutrients. This chapter presents key scientific evidence to outline the optimal nutrient composition for carbohydrates, protein, and fat intake for endurance as well as strength and power athletes.
We have examined hepatic, genomic, and metabolic responses to dietary protein restriction in the non-pregnant Sprague-Dawley rat. Animals were pair-fed either a 6 or 24% casein-based diet for 7-10 days. At the end of the dietary period, a microarray analysis of the liver was performed, followed by validation of the genes of interest. The rates of appearance of phenylalanine, methionine, serine, and glucose and the contribution of pyruvate to serine and glucose were quantified using tracer methods. Plasma and tissue amino acid levels, enzyme activities, and metabolic intermediates were measured. Protein restriction resulted in significant differential expression of a number of genes involved in cell cycle, cell differentiation, transport, transcription, and metabolic processes. RT-PCR showed that the expression of genes involved in serine biosynthesis and fatty acid oxidation was higher, and those involved in fatty acid synthesis and urea synthesis were lower in the liver of protein-restricted animals. Free serine and glycine levels were higher and taurine levels lower in all tissues examined. Tracer isotope studies showed an ∼50% increase in serine de novo synthesis. Pyruvate was the primary (∼90%) source of serine in both groups. Transmethylation of methionine was significantly higher in the protein-restricted group. This was associated with a higher S-adenosylmethionine/S-adenosylhomocysteine ratio and lower cystathione β-synthase and cystathionine γ-lyase activity. Dietary isocaloric protein restriction results in profound changes in hepatic one-carbon metabolism within a short period. These may be related to high methylation demands placed on the organism and caused by possible changes in cellular osmolarity as a result of the efflux of the intracellular taurine.
Background:
Genetic variation in the perilipin (PLIN) gene may play a role in the etiology and treatment of obesity.
Objective:
To examine different polymorphisms in the PLIN gene in relation to body-weight regulation.
Methods:
118 subjects followed a 6 wk VLCD, followed by 1 year weight maintenance. Body-weight (BW), body composition, leptin concentration, and polymorphisms of the PLIN gene: PLIN1:rs2289487, PLIN4:rs894160, PLIN6:rs1052700, PLIN5:rs2304795 and PLIN7:rs 2304796 were determined.
Results:
BW loss during VLCD was 7.0+/-3.1 kg (p<0.05), and BW regain was 3.7+/-1.4 kg (p<0.05), including changes in body mass index (BMI), waist-circumference, body-composition and leptin concentrations (p<0.05). Linkage disequilibria were observed between PLIN1 and PLIN4: D' >0.9, r2=0.72; PLIN5 and PLIN7: D' >0.9, r2=0.85. In men, body weight, BMI, waist circumference, body fat, leptin concentrations were significantly lower for the haplotype of PLIN1 (C-alleles) and PLIN4 (A-alleles). In women weight loss and loss of fat mass were larger for the haplotype of PLIN1 (C-alleles) and PLIN4 (A-alleles). For PLIN6 genotypes body weight and body fat were lower for homozygotes of the minor allele (T/T) in the men; in the women leptin concentrations were lower. The haplotype of PLIN5 and PLIN7 consisting of A/G and G/G of PLIN5 and A/A of PLIN7 showed a reduction in FM: 5.9+/-0.6 kg vs 3.1+/-0.4 kg, % body fat: 5.5+/-0.6% vs 2.2+/-0.2%, and leptin: 20.5+/-10.8 ng/ml vs 12.9+/-6.7 ng/ml over time in the women (p<0.05).
Conclusion:
Since the haplotype of the minor alleles PLIN1-4, PLIN5-7 and PLIN6, was related to body-weight regulation at a lower level of body-weight in the men as well in the women we conclude that the PLIN1-4, 6, and 5-7 locus appears as a genetic influencer of obesity risk in humans.
Whereas diet and exercise have been shown to influence whole-body protein utilization, little is known about the impact of these factors on skeletal-muscle protein turnover. We highlight the role of dietary protein in modulating skeletal-muscle protein turnover in response to endurance exercise. Effects of endurance exercise on skeletal-muscle protein metabolism are presented and the influence of habitual protein intake on exercise-related protein responses is discussed.
Skeletal-muscle protein turnover increases in response to endurance exercise training and following a single endurance exercise bout. Nutritional supplementation postexercise favorably affects skeletal-muscle protein synthesis and demonstrates amino acid availability as pivotal to the skeletal-muscle synthetic response following exercise. The level of habitual protein intake influences postexercise skeletal-muscle protein turnover.
Dietary protein and exercise are powerful stimuli affecting protein turnover. Since variation in habitual protein intake influences skeletal-muscle protein turnover postexercise, investigations are needed to determine what role protein intake has in regulating skeletal-muscle protein metabolism. Long-term, well controlled diet and exercise intervention studies are essential for clarification of the relation between protein intake, endurance exercise, and skeletal-muscle protein turnover. Studies designed to characterize this relationship should be attentive to habitual macronutrient and energy intakes.
This investigation examined the effect of variations in protein intake on whole-body protein turnover (WBPTO) after exercise in endurance-trained males.
Five male runners (21.3 +/- 0.3 yr, 179 +/- 2 cm, 70.6 +/- 0.1 kg, 8.7 +/- 0.4% body fat, 70.6 +/- 0.1 VO2peak) participated in a randomized, crossover-design diet intervention, where they consumed either a low- (0.8 g.kg(-1); LP), moderate- (1.8 g.kg(-1); MP), or high-protein (3.6 g.kg(-1); HP) diet for 4 wk. WBPTO (Ra, leucine rate of appearance; NOLD, nonoxidative leucine disposal; and Ox, leucine oxidation) were assessed after a 75-min run at 70% VO2peak after each diet-intervention period.
Leucine Ra (indicator of protein breakdown) and leucine Ox were greater on the HP diet than on the LP diet (Ra, 123.4 +/- 6.9 vs 97.9 +/- 6.0 micromol.kg(-1).h(-1); Ox, 23.9 +/- 0.5 vs 17.0 +/- 0.8 micromol.kg(-1).h(-1), P < 0.05). No differences were noted in NOLD (an indicator of protein synthesis) across diets. Plasma branched chain amino acids (BCAA) at rest were greater for MP and HP than for LP, and nonessential amino acids (NEAA) were greater for LP than MP at rest and greater than MP and HP after exercise.
Findings from this study show that variations in protein intake can alter plasma amino acid levels and modulate rates of WBPTO after exercise. Additionally, a lower protein intake was associated with decreased rates of WBPTO after exercise.
Previous studies using indirect means to assess the response of protein metabolism to exercise have led to conflicting conclusions. Therefore, in this study we have measured the rate of muscle protein synthesis in normal volunteers at rest, at the end of 4 h of aerobic exercise (40% maximal O2 consumption), and after 4 h of recovery by determining directly the rate of incorporation of 1,2-[13C]leucine into muscle. The rate of muscle protein breakdown was assessed by 3-methylhistidine (3-MH) excretion, and total urinary nitrogen excretion was also measured. There was an insignificant increase in 3-MH excretion in exercise of 37% and a significant increase (P less than 0.05) of 85% during 4 h of recovery from exercise (0.079 +/- 0.008 vs. 0.147 +/- 0.0338 mumol.kg-1.min-1 for rest and recovery from exercise, respectively). Nonetheless, there was no effect of exercise on total nitrogen excretion. Muscle fractional synthetic rate was not different in the exercise vs. the control group at the end of exercise (0.0417 +/- 0.004 vs. 0.0477 +/- 0.010%/h for exercise vs. control), but there was a significant increase in fractional synthetic rate in the exercise group during the recovery period (0.0821 +/- 0.006 vs. 0.0654 +/- 0.012%/h for exercise vs. control, P less than 0.05). Thus we conclude that although aerobic exercise may stimulate muscle protein breakdown, this does not result in a significant depletion of muscle mass because muscle protein synthesis is stimulated in recovery.
The effect of 4 h of exercise at 40% of maximal oxygen consumption (VO2 max) on protein metabolism was assessed in normal volunteers maintained on a diet containing 42 kcal.kg-1.day-1 and either 0.9 or 2.5 g protein.kg-1.day-1. Primed constant infusions of [1,2-13C]-leucine and [15N]glycine enabled the quantitation of whole body protein turnover and also the fractional synthetic rates (FSR) of albumin, fibrinogen, and fibronectin. In subjects who did not exercise, the fractional synthetic rates (%/day) on normal and high-protein intakes, respectively, were as follows: albumin, 10 +/- 1 and 9 +/- 1; fibrinogen, 21 +/- 3 and 18 +/- 1; and fibronectin, 31 +/- 3 and 34 +/- 3. Neither exercise nor recovery had an effect of whole body protein turnover or on albumin FSR, but the FSR of fibronectin was significantly elevated at the end of exercise, and fibrinogen was significantly elevated in recovery. Dietary protein intake had no major effect on the response to exercise. Thus, in response to exercise, there is a stimulation of the synthesis of some acute phase proteins, which may be a mechanism whereby nitrogen resulting from muscle protein breakdown is spared.
The effects of regular submaximal exercise on dietary protein requirements, whole body protein turnover, and urinary 3-methylhistidine were determined in six young (26.8 +/- 1.2 yr) and six middle-aged (52.0 +/- 1.9 yr) endurance-trained men. They consumed 0.6, 0.9, or 1.2 g.kg-1.day-1 of high-quality protein over three separate 10-day periods, while maintaining training and constant body weight. Nitrogen measurements in diet, urine, and stool and estimated sweat and miscellaneous nitrogen losses showed that they were all in negative nitrogen balance at a protein intake of 0.6 g.kg-1.day-1. The estimated protein requirement was 0.94 +/- 0.05 g.kg-1.day-1 for the 12 men, with no effect of age. Whole body protein turnover, using [15N]glycine as a tracer, and 3-methylhistidine excretion were not different in the two groups, despite lower physical activity of the middle-aged men. Protein intake affected whole body protein flux and synthesis but not 3-methylhistidine excretion. These data show that habitual endurance exercise was associated with dietary protein needs greater than the current Recommended Dietary Allowance of 0.8 g.kg-1.day-1. However, whole body protein turnover and 3-methylhistidine excretion were not different from values reported for sedentary men.
Short-term metabolic experiments have revealed that physical exercise increases the oxidation of leucine, which has been interpreted to indicate an increased requirement for dietary protein in physically active subjects. Because it may be inaccurate to extrapolate measurements of amino acid oxidation made over a few hours to the entire day, we have carried out a continuous 24-h intravenous [1-13C]leucine/[15N]urea tracer study in eight healthy adult men. Their diet supplied 1 g protein.kg-1.day-1, and exercise (mean maximal O2 consumption 46%) was for 90 min during the 12-h fast and 12-h fed periods of the day. Subjects were adapted to the diet and exercise regimen for 6 days. Then, on day 7, they were dressed in the University of Uppsala energy metabolic unit's direct calorimeter suit, were connected to an open-hood indirect calorimeter, and received the tracers. Exercise increased leucine oxidation by approximately 50 and 30% over preexercise rates for fast and fed periods, respectively. This increase amounted to approximately 4-7% of daily leucine oxidation. Subjects remained in body leucine equilibrium (balance -4.6 +/- 10.5 mg.kg-1.day-1; -3.6 +/- 8.3% of intake; P = not significant from zero balance). Therefore, moderate exercise did not cause a significant deterioration in leucine homeostasis at a protein intake of 1 g.kg-1.day-1. These findings underscore the importance of carrying out precise, continuous, 24-h measurements of whole body leucine kinetics; this model should be of value in studies concerning the quantitative interactions among physical exercise, energy/protein metabolism, and diet in humans.
Six healthy men completed three 1-hr bouts of treadmill walk-jogging at low (L; 42 +/- 3.9% VO2max), moderate (M; 55 +/- 5.6%), and high (H; 67 +/- 4.5%) exercise intensity in order to determine whether moderate physical activity affects dietary protein needs. Both sweat rate and sweat urea N loss were greater (p < .10) with increasing exercise intensity. Seventy-two hour postexercise urine urea N excretion was elevated (p < .05) over nonexercise control (26.6 +/- 2.96 g) with both M (31.0 +/- 3.65) and H (33.6 +/- 4.39), but not L (26.3 +/- 1.86), intensities. Total 72-hr postexercise urea N excretion (urine + sweat) for the M and H exercise was greater than control by 4.6 and 7.2 g, respectively. This suggests that 1 hr of moderate exercise increases protein oxidation by about 29-45 g, representing approximately 16-25% of the current North American recommendations for daily protein intake. These data indicate that the type of exercise typically recommended for health/wellness can increase daily protein needs relative either to sedentary individuals or to those who exercise at lower intensities.
In healthy adult men adapted to a diet/exercise regimen for 6 days, the effects of small, frequent meals supplying daily protein intakes of 1 (n = 8) or 2.5 g . kg-1 . day-1 (n = 6) on leucine oxidation, urea production, and whole body protein synthesis (PS) and degradation (PD) have been compared with the use of a 24-h continuous intravenous [13C]leucine and [15N,15N]urea infusion protocol. Two 90-min periods of exercise (approximately 50% maximal O2 consumption) were included during the fasting and the fed periods of the 24-h day. Subjects were determined to be at approximate energy, nitrogen, and leucine balances on both diets. Increased protein intake raised the urea production rate; the absolute rate of urea hydrolysis was the same on both diets. When the first-pass splanchnic uptake of leucine was taken to be 25% of intake, PS was stimulated by feeding (after an overnight fast) at both protein intake levels (P < 0.05 and P < 0.01), whereas PD declined significantly (P < 0.01) at both protein levels. Protein gain at a high protein intake appears to be the result of both a stimulation of PS and a marked decline in PD, whereas at a less generous intake, the gain appears to be a result of a fall in PD with a less evident change in PS. Exercise moderately decreased PS during and/or immediately after exercise at each protein level, and there was a postexercise-induced increase (P < 0.01) in PD, which was more dramatic when feeding was at the higher protein intake level.
The aim of this study was to investigate dietary protein-induced changes in whole body leucine turnover and oxidation and in skeletal muscle branched chain 2-oxo acid dehydrogenase (BCOADH) activity, at rest and during exercise. Postabsorptive subjects received a primed constant infusion of L-[1-13C,15N]leucine for 6 h, after previous consumption of a high- (HP; 1.8 g . kg-1 . day-1, n = 8) or a low-protein diet (LP; 0.7 g . kg-1 . day-1, n = 8) for 7 days. The subjects were studied at rest for 2 h, during 2-h exercise at 60% maximum oxygen consumption, then again for 2 h at rest. Exercise induced a doubling of both leucine oxidation from 20 micromol . kg-1 . h-1 and BCOADH percent activation from 7% in all subjects. Leucine oxidation was greater before (+46%) and during (+40%, P < 0.05) the first hour of exercise in subjects consuming the HP rather than the LP diet, but there was no additional change in muscle BCOADH activity. The results suggest that leucine oxidation was increased by previous ingestion of an HP diet, attributable to an increase in leucine availability rather than to a stimulation of the skeletal muscle BCOADH activity.
This paper reviews the factors (exercise intensity, carbohydrate availability, exercise type, energy balance, gender, exercise training, age, and timing of nutrient intake or subsequent exercise sessions) thought to influence protein need. Although there remains some debate, recent evidence suggests that dietary protein need increases with rigorous physical exercise. Those involved in strength training might need to consume as much as 1.6 to 1.7 g protein x kg(-1) x day(-1) (approximately twice the current RDA) while those undergoing endurance training might need about 1.2 to 1.6 g x kg(-1) x day(-1) (approximately 1.5 times the current RDA). Future longitudinal studies are needed to confirm these recommendations and asses whether these protein intakes can enhance exercise performance. Despite the frequently expressed concern about adverse effects of high protein intake, there is no evidence that protein intakes in the range suggested will have adverse effects in healthy individuals.
Both exercise and dietary protein intake affect whole-body protein turnover (WBPTO). Few studies have investigated the effect of aerobic exercise training on WBPTO [leucine rate of appearance (Ra), oxidation (Ox), and nonoxidative leucine disposal (NOLD)] in untrained individuals consuming a specified level of protein. This study examined the effect of aerobic exercise training on WBPTO in untrained men and women during a controlled diet intervention providing 0.88 g protein/(kg . d). After a 2-wk adaptation to the study diet, 7 subjects [3 men, 4 women; 76.1 +/- 5.8 kg, 164.7 +/- 4.4 cm, 30.7 +/- 4.5% body fat, 39.1 +/- 2.8 VO(2max) (maximal oxygen uptake) mL/(kg . min)] participated in 4 wk of aerobic exercise training (running and walking 4-5 times/wk at 65-85% maximal heart rate). WBPTO (determined via constant infusion of 1-[(13)C] leucine), nitrogen balance, and body composition were determined at baseline and after 4 wk of training. Nitrogen balance (-1.0 +/- 0.7 vs. 0.9 +/- 1.1 g N/24 h, P = 0.03) improved with exercise training, whereas body mass and composition did not change. Leucine Ra did not change, Ox decreased [18 +/- 2 to 15 +/- 2 micromol/(kg . h), P </= 0.001], and NOLD tended to increase [128 +/- 18 to 151 +/- 19 micromol/(kg . h), P = 0.09] in response to training. These data indicate improved protein utilization in response to exercise training in weight-stable subjects. This study emphasizes the importance of dietary control, with specific regard to energy and protein intakes, in the characterization of protein utilization in response to an exercise intervention.
In brief: The use of proteins as a source of energy has been discounted in the past. However, current research has demonstrated that amino acids can contribute to whole body metabolism. The availability of amino acids can be increased by either elevating the rate of muscle protein breakdown or decreasing the rate of muscle protein synthesis. Research indicates that there is a substantial decrease in the rate of protein synthesis during exercise. We estimate that protein can provide up to 5.5% of the total caloric cost of exercise. Because essential amino acid requirements have been determined only for resting persons, the recommended maximum protein requirements may not be adequate for physically active individuals.
Whole body leucine kinetics was compared in endurance-trained athletes an sedentary controls matched for age, gender, and body weight. When leucine kinetics were expressed both per unit of body weight and per unit of fat-free mass, both groups demonstrated an increase in leucine oxidation during exercise. However, the between group differences were eliminated when leucine kinetics were corrected for fat-free tissue mass. Therefore, correction of leucine kinetics for far-free mass maybe important when cross-sectional investigations on humans are performed. It is concluded that there was no difference between endurance-trained and sedentary humans in whole body leucine kinetics during rest, exercise, or recovery when expressed per unit of FFM.
We studied postexercise amino acid metabolism, in the whole body and across the forearm. Seven volunteers were infused with L-[alpha-15N]lysine and L-[1-13C]-leucine twice [one time during 3 h after cycle exercise (75% VO2max), and one time in the resting state]. Whole body protein breakdown was estimated from dilution of L-[alpha-15N]lysine and L-[1-13C]ketoisocaproic acid (KIC) enrichments in plasma. Leucine oxidation was calculated from 13CO2 enrichments in expired air. Whole body protein breakdown was not increased above resting levels during the recovery period. Leucine oxidation was decreased after exercise (postexercise 13 +/- 2.3 vs. resting 19 +/- 3.2 mumol.kg-1.h-1; P less than 0.02), while nonoxidative leucine disposal was increased (115 +/- 6.1 vs. 103 +/- 5.6 micrograms.kg-1.min-1; P less than 0.02). After exercise, forearm net lysine balance was unchanged (87 +/- 25 vs. 93 +/- 28 nmol.100 ml-1.min-1), but there were decreases in forearm muscle protein degradation (219 +/- 51 vs. 356 +/- 85 nmol.100 ml-1.min-1; P less than 0.05) and synthesis (132 +/- 41 vs. 255 +/- 69 nmol.100 ml-1.min-1; P less than 0.01). In conclusion, after exercise 1) whole body protein degradation is not increased, 2) leucine disposal is directed away from oxidative and toward nonoxidative pathways, 3) forearm protein synthesis is decreased. Postexercise increases in whole body protein synthesis occur in tissues other than nonexercised muscle.
The effects of gender on substrate utilization during prolonged submaximal exercise were studied in six males and six equally trained females. After 3 days on a controlled diet (so that the proportions of carbohydrate, protein, and fat were identical), subjects ran on a treadmill at a velocity requiring an O2 consumption of approximately 65% of maximal. They ran a total "distance" of 15.5 km with a range in performance time of 90-101 min. Plasma glycerol, glucose, free fatty acids, and selected hormones (catecholamines, growth hormone, insulin, and glucagon) were measured throughout and after the run by sampling from an indwelling venous catheter, and glycogen utilization was calculated from pre- and postexercise needle biopsies of vastus lateralis. Exercise protein catabolism was estimated from 24-h urinary urea nitrogen excretion over the test day and a nonexercise day. The males were found to have significantly higher respiratory exchange ratios (mean 0.94 vs. 0.87), greater muscle glycogen utilization (by 25%), and greater urea nitrogen excretion (by 30%) than the females. No gender differences were evident in the hormonal response to the exercise with the exception of a lower insulin concentration and a higher epinephrine concentration in the males. We conclude that, during moderate-intensity long-duration exercise, females demonstrate greater lipid utilization and less carbohydrate and protein metabolism than equally trained and nourished males.
This study compared whole-body leucine kinetics in endurance-trained (TRN) and sedentary (SED) control subjects. Eleven men and women (6 TRN, 5 SED) underwent a 6-h primed, constant-rate infusion of L-[1-13C]leucine. Leucine turnover and oxidation were measured using tracer dilution and by measuring 13C enrichment of expired CO2 combined with respiratory calorimetry. Whole-body leucine turnover was greater in the TRN subjects (P less than 0.004; TRN 98.3 +/- 5.0, SED 75.3 +/- 4.2 mumol.kg-1.h-1; mean +/- SE), but there was no difference between groups in leucine oxidation (TRN 13.1 +/- 0.97, SED 11.5 +/- 0.48 mumol.kg-1.h-1). Thus more leucine turnover was available for nonoxidative utilization. In addition, the TRN subjects had higher resting energy expenditures compared with the SED group, and when all subjects were included in the analysis, there was a significant correlation between energy expenditure and protein turnover (n = 11, R = 0.61, P = 0.05). Therefore the heightened resting energy expenditure in the TRN subjects may be accounted for by an increased whole-body protein turnover. These results suggest that endurance training results in increased leucine and/or protein turnover, which may contribute to the increased resting energy expenditure observed in these subjects.
This study examined whether variability among healthy young adults in resting metabolic rate, normalized for the amount of metabolically active tissue (assessed by total body potassium), is related to protein turnover. Resting metabolic rate was measured by indirect calorimetry for 2 h in 26 men and 21 women, 19-33 yr old, with simultaneous estimation of protein turnover during a 4-h infusion of L-[1-13C]leucine. After adjusting metabolic rate for total body potassium, the standard deviation was only 89 kcal/day, or 5.5% of the average value. There was a high correlation between leucine flux (an index of proteolysis) and metabolic rate (r = 0.84) and between the nonoxidized portion of leucine flux (an index of protein synthesis) and metabolic rate (r = 0.83). This relationship was weaker, but still significant, after adjusting leucine metabolism and metabolic rate for total body potassium (r = 0.36 for leucine flux vs. metabolic rate, r = 0.33 for nonoxidized portion of leucine flux vs. metabolic rate, P less than 0.05). The regression analysis suggested that the contribution of protein turnover to resting metabolic rate was approximately 20% in an average subject. Metabolic rate and protein turnover were highest in the subjects with the greatest amount of body fat, even after accounting for differences in whole body potassium. Neither resting metabolic rate nor protein turnover was related to total or free concentrations of thyroxine or triiodothyronine, within the euthyroid range.(ABSTRACT TRUNCATED AT 250 WORDS)
On two separate occasions, five well-trained endurance runners (VO2max = 71 +/- 5 ml/kg/min; means +/- SD) consumed a meat-free diet for 6 days. For one trial the subjects consumed the recommended dietary allowance (RDA) of protein (REC-PRO = 0.86 +/- 0.23 g/kg body wt/day). Protein intake for the other trial was 1.7 times higher (HI-PRO = 1.49 +/- 0.29 g/kg body wt/day). Each subject followed his regular training program (12-16 km running/day), and on day 5 of each diet completed a treadmill run at a similar intensity and duration (75 min at 72% VO2max). Seventy-two hour urinary urea N loss (days 4, 5, and 6 of each diet) and day 5 exercise sweat urea N excretion were measured. Serum urea N and creatinine increased significantly during the treadmill run under both dietary conditions (P less than 0.05). No significances between diet differences were observed in sweat or urinary urea N excretion; however, excretion of both tended to be higher on the REC-PRO diet than on the HI-PRO diet. The differences in protein intake combined with the nitrogen excretion measures resulted in significant differences in estimated whole-body nitrogen retention between the two treatments. Nitrogen retention (means +/- SE) remained positive during the HI-PRO trial (2.41 +/- 1.99 g/day) but was significantly (P less than 0.005) reduced to -5.29 +/- 2.58 g/day during the REC-PRO trial. These results suggest that the current protein RDA may be inadequate for athletes engaging in chronic high-intensity endurance exercise. Future studies are needed to confirm this observation.
The present study examined the effects of training status (endurance exercise or body building) on nitrogen balance, body composition, and urea excretion during periods of habitual and altered protein intakes. Experiments were performed on six elite bodybuilders, six elite endurance athletes, and six sedentary controls during a 10-day period of normal protein intake followed by a 10-day period of altered protein intake. The nitrogen balance data revealed that bodybuilders required 1.12 times and endurance athletes required 1.67 times more daily protein than sedentary controls. Lean body mass (density) was maintained in bodybuilders consuming 1.05 g protein.kg-1.day-1. Endurance athletes excreted more total daily urea than either bodybuilders or controls. We conclude that bodybuilders during habitual training require a daily protein intake only slightly greater than that for sedentary individuals in the maintenance of lean body mass and that endurance athletes require daily protein intakes greater than either bodybuilders or sedentary individuals to meet the needs of protein catabolism during exercise.
Two studies were conducted to investigate the effects of mild exercise on nitrogen balance in men given diets supplying adequate or slightly limiting energy. In experiment A the diet supplied 91 mg N/kg body weight (0.57 g protein/kg, the FAO/WHO safe level of intake) as egg white; in experiment B the same source was used to provide the 1980 NRC-RDA for adult males, 128 mg N/kg body weight (0.8 g protein/kg). By adjusting energy intake and activity, periods of energy equilibrium and negative energy balance (-15%) were achieved at three levels of activity (X for exercise): no programmed work (0.85X), 1 hour of treadmill walking (1.0X) and 1 hour each of treadmill and cycle ergometry (1.15X). "True" nitrogen balance (TNbal) was more positive or less negative during periods of energy equilibrium as compared to those of energy deficit. This effect of energy balance on TNbal increased with physical activity. At the lower protein intake the mean difference in TNbal between the period of energy equilibrium and that of energy deficit at 1.0X was 0.19 g N/day (nonsignificant difference) and 0.54 g N/day at 1.15X. When protein intake was increased, the difference in TNbal between periods of equilibrium and deficit was significant at all levels of activity: 0.65 g N/day at 0.85X, 0.93 g N/day at 1.0X and 1.09 g N/day at 1.15X. Physical activity was anabolic when energy balance was maintained. In experiment A the addition of 1 hour of exercise (1.0X to 1.15X) spared 2.5 mg N/kg body weight; reducing activity by 1 hour (1.0X to 0.85X) cost 1.4 mg N/kg body weight. In experiment B, TNbal was more positive with increased activity (by 5.9 mg N/kg body weight) and more negative (by 11.5 mg N/kg body weight) when the men were sedentary. During periods of energy deficit, the anabolic effect of activity was also present, although less markedly. When activity increased from 1 to 2 hours in experiment A, TNbal improved by 2.1 mg N/kg body weight and in experiment B, by 3.5 mg N/kg body weight. Thus, circumstances of negative energy balance with adequate protein intake are better tolerated when the energy deficit is generated by physical activity than when it derives from reduced intake; the picture when protein intake is marginal requires further investigation.
Protein utilization in young men under circumstances of one or two periods of work and both adequate and surfeit energy intake was determined by nitrogen balance; protein intake was constant at the FAO/WHO (1973) safe level (0.57 g/kg body-weight). Physical activity affected protein utilization negatively by increasing sweat and faecal N losses, and positively by supporting increased energy intake. Efficiency with which surfeit energy improved N utilization (mg N retained/added kJ) was greater under circumstances of increased activity. Changes in body composition as determined by total body potassium and hydrostatic weighing supported the N retention values.
We have used the primed constant infusion of di-[15N]urea and [1-13C]leucine to determine the effects of mild exercise (approx 30% Vo2max for 105 min) on urea production and leucine metabolism in human subjects. The oxidation of plasma leucine was distinguished from the oxidation of leucine that never entered the plasma pool ("intracellular" leucine) by means of determining the enrichment of alpha-ketoisocaproic acid (alpha-KICA). Total leucine oxidation increased from 0.38 +/0 0.05 to 1.41 +/- 0.14 micromol . kg-1 . min-1 during exercise due to increases in the oxidation of plasma leucine (150%) and intracellular leucine (600%). Plasma leucine flux decreased slightly, but not significantly (0.1 greater than P greater than 0.05), and the percent of alpha-KICA derived from plasma leucine dropped significantly (P less than 0.05) from 79.5 +/- 4.3 at rest to 62.0 +/- 5.3% over the last 30 min of exercise. Despite the increase in leucine oxidation during exercise, urea concentration and production did not change. Thus in exercise urea production does not accurately reflect all aspects of amino acid metabolism.
1. We have investigated the effects of moderate long-term exercise on protein turnover in fed man by measuring the extent of whole-body nitrogen production, the labelling of urinary ammonia from ingested [15N]glycine and plasma, muscle and urine free amino acid concentrations.
2. Judged both from nitrogen production, and from the extent of 13CO2 production from ingested l-[l-13C]leucine, exercise causes a substantial rise in amino acid catabolism.
3. Amino acids catabolized during exercise appear to become available through a fall in whole-body protein synthesis and a rise in whole-body protein breakdown. After exercise, protein balance becomes positive through a rise in the rate of whole-body synthesis in excess of breakdown.
4. Studies of free 3-methylhistidine in muscle, plasma and urine samples suggest that exercise decreases the fractional rate of myofibrillar protein breakdown, in contrast with the apparent rise in whole-body breakdown.
During endurance exercise at approximately 65% maximal O2 consumption, women oxidize more lipids, and therefore decrease carbohydrate and protein oxidation, compared with men (L.J. Tarnopolsky, M.A. Tarnopolsky, S.A. Atkinson, and J.D. MacDougall. J. Appl. Physiol. 68: 302-308, 1990; S.M. Phillips, S.A. Atkinson, M.A. Tarnopolsky, and J.D. MacDougall. J. Appl. Physiol. 75: 2134-2141, 1993). The main purpose of this study was to examine the ability of similarly trained male (n = 7) and female (n = 8) endurance athletes to increase muscle glycogen concentrations in response to an increase in dietary carbohydrate from 55-60 to 75% of energy intake for a period of 4 days (carbohydrate loading). In addition, we sought to examine whether gender differences existed in metabolism during submaximal endurance cycling at 75% peak O2 consumption (VO2 peak) for 60 min. The men increased muscle glycogen concentration by 41% in response to the dietary manipulation and had a corresponding increase in performance time during an 85% VO2 peak trial (45%), whereas the women did not increase glycogen concentration (0%) or performance time (5%). The women oxidized significantly more lipid and less carbohydrate and protein compared with the men during exercise at 75% VO2-peak. We conclude that women did not increase muscle glycogen in response to the 4-day regimen of carbohydrate loading described. In addition, these data support previous observations of greater lipid and lower carbohydrate and protein oxidation by women vs. men during submaximal endurance exercise.
The effect of the amount of protein intake (12% and 21% of total energy intake, diet A and diet B, respectively) on nitrogen balance and whole-body protein turnover (PT) was measured in 19 young men and 10 young women (aged 30 +/- 5 and 27 +/- 4 y, respectively). In young adults, mean nitrogen balance was approximately zero during diet A whereas it was positive during diet B. In young adults, PT was significantly higher during diet B in comparison with diet A. This was also seen in elderly subjects, as described before. From a comparison of the current data with the data previously obtained in elderly subjects it can be concluded that during diet A young adults had PT rates higher than those of elderly subjects. During diet B, PT of young men was comparable with the PT of elderly men whereas young women still had higher PT rates than elderly women (even when corrections were made for differences in body composition).
The current Canadian Recommended Nutrient Intake (RNI) for protein (0.86 g.kg-1.day-1) makes no allowance for an effect of habitual physical activity. In addition, Tarnopolsky et al. (J. Appl. Physiol. 68: 302-308, 1990) showed that males may catabolize more protein than females consequent to endurance exercise. We examined nitrogen (N) balance and leucine kinetics during submaximal endurance exercise to determine the adequacy of the current Canadian RNI for protein for male and female endurance athletes. Athletes were matched for equal training volume, competitive status, and conditioning and were fed diets isoenergetic with their habitual intake, containing protein at the Canadian RNI. Subjects were adapted to the diet for 10 days before completing a 3-day measurement of N balance. N balance showed that the RNI was inadequate for females (-15.9 +/- 6.0 mg.kg-1.day-1) and males (-26.3 +/- 11.0 mg.kg-1.day-1). Leucine kinetics during exercise were determined for each subject on day 3 of the N balance experiment by use of a primed continuous infusion of L-[1-13C]leucine and the reciprocal pool model. Exercise resulted in a significant (P < 0.01) increase in leucine oxidation for both groups. Males oxidized a greater amount of leucine during the infusion than females (P < 0.01). Leucine flux also increased significantly (P < 0.01) during exercise in both groups. We conclude that the current Canadian RNI for protein is inadequate for those who chronically engage in endurance exercise.(ABSTRACT TRUNCATED AT 250 WORDS)
There is little known about the responses of muscle protein metabolism in women to exercise. Furthermore, the effect of adding resistance training to an endurance training regimen on net protein anabolism has not been established in either men or women. The purpose of this study was to quantify the acute effects of combined swimming and resistance training on protein metabolism in female swimmers by the direct measurement of muscle protein synthesis and whole body protein degradation. Seven collegiate female swimmers were each studied on four separate occasions with a primed constant infusion of ring-[13C6]phenylalanine (Phe) to measure the fractional synthetic rate (FSR) of the posterior deltoid and whole body protein breakdown. Measurements were made over a 5-h period at rest and after each of three randomly ordered workouts: 1) 4,600 m of intense interval swimming (SW); 2) a whole body resistance-training workout with no swimming on that day (RW); and 3) swimming and resistance training combined (SR). Whole body protein breakdown was similar for all treatments (0.75 +/- 0.04, 0.69 +/- 0.03, 0.69 +/- 0.02, and 0.71 +/- 0.04 mumol.min-1.kg-1 for rest, RW, SW, and SR, respectively). The FSR of the posterior deltoid was significantly greater (P < 0.05) after SR (0.082 +/- 0.015%/h) than at rest (0.045 +/- 0.006%/h). There was no significant difference in the FSR after RW (0.048 +/- 0.004%/h) or SW (0.064 +/- 0.008%/h) from rest or from SR. These data indicate that the combination of swimming and resistance exercise stimulates net muscle protein synthesis above resting levels in female swimmers.
Whole body leucine kinetics was compared in endurance-trained athletes and sedentary controls matched for age, gender, and body weight. Kinetic studies were performed during 3 h of rest, 1 h of exercise (50% maximal oxygen consumption), and 2 h of recovery. When leucine kinetics were expressed both per unit of body weight and per unit of fat-free mass, both groups demonstrated an increase in leucine oxidation during exercise (P < 0.01). Trained athletes had a greater leucine rate of appearance during exercise and recovery compared with their sedentary counterparts (P < 0.05) and an increased leucine oxidation at all times on the basis of body weight (P < 0.05). However, all of these between-group differences were eliminated when leucine kinetics were corrected for fat-free tissue mass. Therefore, correction of leucine kinetics for fat-free mass may be important when cross-sectional investigations on humans are performed. Furthermore, leucine oxidation, when expressed relative to whole-body oxygen consumption during exercise, was similar between groups. It is concluded that there was no difference between endurance-trained and sedentary humans in whole body leucine kinetics during rest, exercise, or recovery when expressed per unit of fat-free tissue mass.
We studied the effects of a 38-day endurance exercise training program on leucine turnover and substrate metabolism during a 90-min exercise bout at 60% peak O(2) consumption (VO(2 peak)) in 6 males and 6 females. Subjects were studied at both the same absolute (ABS) and relative (REL) exercise intensities posttraining. Training resulted in a significant increase in whole body VO(2 peak) and skeletal muscle citrate synthase (CS; P < 0.001), complex I-III (P < 0.05), and total branched-chain 2-oxoacid dehydrogenase (BCOAD; P < 0.001) activities. Leucine oxidation increased during exercise for the pretraining trial (PRE, P < 0.001); however, there was no increase for either the ABS or REL posttraining trial. Leucine oxidation was significantly lower for females at all time points during rest and exercise (P < 0.01). The percentage of BCOAD in the activated state was significantly increased after exercise for both the PRE and REL exercise trials, with the increase in PRE being greater (P < 0.001) compared with REL (P < 0.05). Females oxidized proportionately more lipid and less carbohydrate during exercise compared with males. In conclusion, we found that 38 days of endurance exercise training significantly attenuated both leucine oxidation and BCOAD activation during 90 min of endurance exercise at 60% VO(2 peak) for both ABS and REL exercise intensities. Furthermore, females oxidize proportionately more lipid and less carbohydrate compared with males during endurance exercise.
Based on an intensive review of published observations on protein intake in the presence of a reduced caloric intake, certain conclusions seem clear.
For young, essentially normal active men, when no protein is fed the protein deficit (negative nitrogen balance) can be maximally reduced by supplying about 700 nonprotein calories. No significant protein-sparing is achieved by intake as high as 2800 calories in the absence of protein. When the caloric intake is approximately 1000, 3 Gm. of nitrogen will produce as much protein sparing as higher quantities of nitrogen. When full caloric requirement is met, 8.5 Gm. of nitrogen promotes balance and little additional storage results even from much larger protein intakes.
These findings, plus others cited from the literature, suggest that a versatile food unit of 500 calories (7 to 8 per cent of which are derived from protein) would be most practical and physiological in the development of a military survival ration, or a short-term civilian emergency feeding.
Prolonged endurance exercise stimulates whole-body protein turnover (synthesis and degradation) but it remains contentious whether this translates into an increased net protein oxidation or dietary requirement for protein. Skeletal muscle is the major energy consumer during exercise and the oxidation of branched-chain amino acids (BCAA) is increased several-fold, suggesting an increased requirement for fuel. Increased BCAA oxidation has been proposed to impair aerobic energy provision during prolonged exercise, but there is little evidence to support this theory. Endurance training blunts the acute exercise-induced increase in whole-body protein turnover and skeletal BCAA oxidation at a given work intensity. However, training also increases the maximal capacity for skeletal muscle BCAA oxidation, as evidenced by a higher maximal activity of the rate-determining enzyme branched-chain oxo acid dehydrogenase. Exercise-induced changes in protein metabolism are affected by nutritional status, with high carbohydrate availability (as typically practiced by endurance athletes) generally associated with reduced net protein utilisation. Ingestion of protein with carbohydrate improves net protein balance during exercise and recovery compared with carbohydrate alone, but it remains to be determined whether this practice facilitates the adaptive response to chronic training.
Effect of exercise and recovery on muscle protein synthesis in human subjects Gender differences in leucine kinetics and nitrogen balance in endurance athletes
- F Carraro
- Ca Stuart
- Wh Hartl
- J Rosenblatt
- Wolfe
- Phillips
- Sm
- Atkinson
- Sa
- Ma Tarnopolsky
- Macdougall
Carraro F, Stuart CA, Hartl WH, Rosenblatt J, Wolfe RR. Effect of exercise and recovery on muscle protein synthesis in human subjects. Am J Physiol 1990;259:E470 -6. [13] Phillips SM, Atkinson SA, Tarnopolsky MA, MacDougall JD. Gender differences in leucine kinetics and nitrogen balance in endurance athletes. J Appl Physiol 1993;75:2134 -41.
Increased dietary protein affects hydration indices in endurance runners
- W F Martin
- D R Bolster
- P C Gaine
- L J Hanley
- M A Pikosky
- B T Bennett
Martin WF, Bolster DR, Gaine PC, Hanley LJ, Pikosky MA, Bennett BT, et al. Increased dietary protein affects hydration indices in endurance runners. J American Dietetic Association (in press).
American Dietetic Association, and Dietitians of Canada Joint position statement: nutrition and athletic performance
American College of Sports Medicine, American Dietetic Association,
and Dietitians of Canada. Joint position statement: nutrition and
athletic performance. Med Sci Sports Exerc 2000;32:2130 -45.
Joint position statement: nutrition and athletic performance
- American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada