Protein requirements may be lower on a training compared to rest day but are not influenced by moderate training volumes in endurance trained males

The impact of training volume on protein requirements in endurance trained males was investigated with indicator amino acid oxidation (IAAO) methodology on a recovery day (REST) or after a 10- or 20-km run while consuming a single suboptimal protein intake (0.93 g/kg/d). Phenylalanine excretion (F13CO2; inverse proxy for whole body protein synthesis) was greatest and phenylalanine net balance was lowest on REST compared to post-exercise recovery with no difference between training volumes. Single point F13CO2 was indistinguishable from past IAAO studies using multiple protein intakes. Our results suggest protein requirements may be greatest on recovery days but are not influenced by moderate training volumes in endurance athletes.

Greater plasma essential amino acids and lower 3-methylhistidine with higher protein intake during endurance training: a randomised control trial

Endurance exercise alters amino acid (AA) metabolism that necessitates greater AA intake in the post exercise recovery period to support recovery. Thus, daily AA ingestion during a period of endurance training may affect the metabolically active plasma free AA pool, which is otherwise maintained during periods of inadequate protein intake by the breakdown of skeletal muscle proteins. Nine endurance-trained males completed a 4-day running protocol (20 km, 5 km, 10 km and 20 km on days 1-4, respectively) on three occasions with a controlled diet providing different protein intakes [0.94(LOW), 1.20(MOD) or 1.83gprotein kgbody mass-1 day-1 (HIGH)]. Urine collected over 24 h on day-4 and plasma collected after an overnight fast on day-5 were analyzed for free AA (plasma) and 3-methylhistidine (3MH; plasma and urine), a marker of myofibrillar protein breakdown. There was an effect of protein intake (HIGH > MOD/LOW; P < 0.05) on fasted plasma essential AA, branched chain AA and 3MH but no effect on 24-h urinary 3-MH excretion. Consuming a previously determined optimal daily protein intake of 1.83 g kg-1 day-1 during endurance training maintains fasted plasma free AA and may attenuate myofibrillar protein catabolism, although this latter effect was not detected in 24-h urinary excretion. The maintenance of the metabolically active free plasma AA pool may support greater recovery from exercise and contribute to the previously determined greater whole-body net protein balance in this athletic population. TRN: NCT02801344 (June 15, 2016).

Protein Intake to Maximize Whole-Body Anabolism during Postexercise Recovery in Resistance-Trained Men with High Habitual Intakes is Severalfold Greater than the Current Recommended Dietary Allowance

BACKGROUND

Dietary protein supports resistance exercise-induced anabolism primarily via the stimulation of protein synthesis rates. The indicator amino acid oxidation (IAAO) technique provides a noninvasive estimate of the protein intake that maximizes whole-body protein synthesis rates and net protein balance.

OBJECTIVE

We utilized IAAO to determine the maximal anabolic response to postexercise protein ingestion in resistance-trained men.

METHODS

Seven resistance-trained men (mean ± SD age 24 ± 3 y; weight 80 ± 9 kg; 11 ± 5% body fat; habitual protein intake 2.3 ± 0.6 g·kg-1·d-1) performed a bout of whole-body resistance exercise prior to ingesting hourly mixed meals, which provided a variable amount of protein (0.20-3.00 g·kg-1·d-1) as crystalline amino acids modeled after egg protein. Steady-state protein kinetics were modeled with oral l-[1-13C]-phenylalanine. Breath and urine samples were taken at isotopic steady state to determine phenylalanine flux (PheRa), phenylalanine excretion (F13CO2; reciprocal of protein synthesis), and net balance (protein synthesis - PheRa). Total amino acid oxidation was estimated from the ratio of urinary urea and creatinine.

RESULTS

Mixed model biphasic linear regression revealed a plateau in F13CO2 (mean: 2.00; 95% CI: 1.62, 2.38 g protein·kg-1·d-1) (r2 = 0.64; P ˂ 0.01) and in net balance (mean: 2.01; 95% CI: 1.44, 2.57 g protein·kg-1·d-1) (r2 = 0.63; P ˂ 0.01). Ratios of urinary urea and creatinine concentrations increased linearly (r = 0.84; P ˂ 0.01) across the range of protein intakes.

CONCLUSIONS

A breakpoint protein intake of ∼2.0 g·kg-1·d-1, which maximized whole-body anabolism in resistance-trained men after exercise, is greater than previous IAAO-derived estimates for nonexercising men and is at the upper range of current general protein recommendations for athletes. The capacity to enhance whole-body net balance may be greater than previously suggested to maximize muscle protein synthesis in resistance-trained athletes accustomed to a high habitual protein intake. This trial was registered at clinicaltrials.gov as NCT03696264.

Protein to Maximize Whole-Body Anabolism in Resistance-trained Females after Exercise

INTRODUCTION

Current athlete-specific protein recommendations are based almost exclusively on research in males.

PURPOSE

Using the minimally invasive indicator amino acid oxidation technique, we determined the daily protein intake that maximizes whole-body protein synthesis (PS) and net protein balance (NB) after exercise in strength-trained females.

METHODS

Eight resistance-trained females (23 ± 3.5 yr, 67.0 ± 7.7 kg, 163.3 ± 3.7 cm, 24.4% ± 6.9% body fat; mean ± SD) completed a 2-d controlled diet during the luteal phase before performing an acute bout of whole-body resistance exercise. During recovery, participants consumed eight hourly meals providing a randomized test protein intake (0.2-2.9 g·kg·d) as crystalline amino acids modeled after egg protein, with constant phenylalanine (30.5 mg·kg·d) and excess tyrosine (40.0 mg·kg·d) intakes. Steady-state whole-body phenylalanine rate of appearance (Ra), oxidation (Ox; the reciprocal of PS), and NB (PS - Ra) were determined from oral [C] phenylalanine ingestion. Total protein oxidation was estimated from the urinary urea-creatinine ratio (U/Cr).

RESULTS

A mixed model biphase linear regression revealed a break point (i.e., estimated average requirement) of 1.49 ± 0.44 g·kg·d (mean ± 95% confidence interval) in Ox (r = 0.64) and 1.53 ± 0.32 g·kg·d in NB (r = 0.65), indicating a saturation in whole-body anabolism. U/Cr increased linearly with protein intake (r = 0.56, P < 0.01).

CONCLUSIONS

Findings from this investigation indicate that the safe protein intake (upper 95% confidence interval) to maximize anabolism and minimize protein oxidation for strength-trained females during the early ~8-h postexercise recovery period is at the upper end of the recommendations of the American College of Sports Medicine for athletes (i.e., 1.2-2.0 g·kg·d).

The Effect of Dietary Protein on Protein Metabolism and Performance in Endurance-trained Males

Recommendations for dietary protein are primarily based on intakes that maintain nitrogen (i.e., protein) balance rather than optimize metabolism and/or performance.

PURPOSE

This study aimed 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; V˙O2peak, 65.9 ± 7.9 mL O2·kg·min) performed three trials consisting of 4 d of controlled training (20, 5, 10, and 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, breakdown, and net balance 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, 5-km time trial, and countermovement jump impulse (IMP) and peak force before and immediately after the 4-d intervention.

RESULTS

Synthesis and breakdown were not affected by protein intake, whereas net balance 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) toward an interaction in 5-km Time Trial with HIGH having a moderate effect over LOW (effect size = 0.57) and small effect over MOD (effect size = 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 maximum voluntary isometric contraction, IMP, or peak force performance.

CONCLUSION

Our data suggest that athletes who consume dietary protein toward the upper end of the current recommendations by the American College of Sports Medicine (1.2-2 g·kg) would better maintain protein metabolism and potentially exercise performance during training.

Whole-body net protein balance plateaus in response to increasing protein intakes during post-exercise recovery in adults and adolescents

Background

Muscle protein synthesis and muscle net balance plateau after moderate protein ingestion in adults. However, it has been suggested that there is no practical limit to the anabolic response of whole-body net balance to dietary protein. Moreover, limited research has addressed the anabolic response to dietary protein in adolescents. The present study determined whether whole-body net balance plateaued in response to increasing protein intakes during post-exercise recovery and whether there were age- and/or sex-related dimorphisms in the anabolic response.

Methods

Thirteen adults [7 males (M), 6 females (F)] and 14 adolescents [7 males (AM), 7 females (AF) within ~ 0.4 y from peak height velocity] performed ~ 1 h variable intensity exercise (i.e., Loughborough Intermittent Shuttle Test) prior to ingesting hourly mixed meals that provided a variable amount of protein (0.02-0.25 g·kg^- 1·h^- 1) as crystalline amino acids modeled after egg protein. Steady-state protein kinetics were modeled noninvasively with oral L-[1-¹³C]phenylalanine. Breath and urine samples were taken at plateau to determine phenylalanine oxidation and flux (estimate of protein breakdown), respectively. Whole-body net balance was determined by the difference between protein synthesis (flux - oxidation) and protein breakdown. Total amino acid oxidation was estimated from the ratio of urinary urea/creatinine.

Results

Mixed model biphasic linear regression explained a greater proportion of net balance variance than linear regression (all, r ² ≥ 0.56; P < 0.01), indicating an anabolic plateau. Net balance was maximized at ~ 0.15, 0.12, 0.12, and 0.11 g protein·kg^- 1·h^- 1 in M, F, AM, and AF, respectively. When collapsed across age, the y-intercept (net balance at very low protein intake) was greater (overlapping CI did not contain zero) in adolescents vs. adults. Urea/creatinine excretion increased linearly (all, r ≥ 0.76; P < 0.01) across the range of protein intakes. At plateau, net balance was greater (P < 0.05) in AM vs. M.

Conclusions

Our data suggest there is a practical limit to the anabolic response to protein ingestion within a mixed meal and that higher intakes lead to deamination and oxidation of excess amino acids. Consistent with a need to support lean mass growth, adolescents appear to have greater anabolic sensitivity and a greater capacity to assimilate dietary amino acids than adults.

Protein Intake at Breakfast Promotes a Positive Whole-Body Protein Balance in a Dose-Response Manner in Healthy Children: A Randomized Trial

Background

Protein ingestion promotes whole-body net protein balance (NB) in children, which is a prerequisite for growth. Determining how much protein is required at breakfast to promote a positive NB, which may be negative after the traditional overnight fast in children, has yet to be determined.

Objective

We determined the impact of incremental doses of milk protein at breakfast as well as the impact of daily dietary protein distribution on NB in children.

Methods

A total of 28 children [14 boys, 14 girls; age range: 7-11 y; body mass index (mean ± SD, in kg/m2): 16.0 ± 1.9] completed 2 intervention trials. During the breakfast meal, participants consumed an isoenergetic beverage with different amounts of protein (0, 7, 14, or 21 g for Groups A-D, respectively) and [15N]-glycine to measure whole body protein metabolism. Whole-body nitrogen turnover, protein synthesis (PS), protein breakdown, and NB were measured over 9 and 24 h.

Results

Following an overnight fast, children were in negative NB (-64.5 mg · kg-1 · h-1). Protein ingestion at breakfast induced a stepwise increase in NB over 9 h [Groups A (6.2 mg · kg-1 · h-1) < B (27.9 mg · kg-1 · h-1) < C (46.9 mg · kg-1 · h-1) < D (66.0 mg · kg-1 · h-1)] with all conditions different from each other (all P < 0.01). PS was 42% greater in Group D than in Group A over 9 h (P < 0.05).

Conclusions

Consuming ≥7 g of the total daily protein intake at breakfast attenuates the observed overnight protein losses in children during the subsequent 9 h following breakfast consumption. The dose-dependent increase in NB over a daytime fed period, inclusive of breakfast and lunch, highlights the importance of breakfast protein intake on acute anabolism in healthy active children. This trial was registered at clinicaltrials.gov as NCT02465151.

Timing and pattern of postexercise protein ingestion affects whole-body protein balance in healthy children: a randomized trial

The dose and timing of postexercise protein ingestion can influence whole-body protein balance (WBPB) in adults, although comparable data from children are scarce. This study investigated how protein intake (both amount and distribution) postexercise can affect WBPB in physically active children. Thirty-five children (26 males; 9-13 years old) underwent a 5-day adaptation diet, maintaining a protein intake of 0.95 g·kg^-1·day^-1. Participants consumed [¹⁵N]glycine (2 mg·kg^-1) before performing 3 × 20 min of variable-intensity cycling, and whole-body protein kinetics were assessed over 6 and 24 h of recovery. Fifteen grams of protein was distributed across 2 isoenergetic carbohydrate-containing beverages (15 and 240 min postexercise) containing reciprocal amounts of protein (i.e., 0 + 15 g, 5 + 10 g, 10 + 5 g, and 15 + 0 g for Groups A-D, respectively). Over the 6 h that included the exercise bout and consumption of the first beverage at 15 min postexercise, WBPB (i.e., synthesis - breakdown) demonstrated a linear increase of 0.647 g·kg^-1·day^-1 per 1 g protein intake (P < 0.001). Over 24 h, robust regression revealed that WBPB was best modeled by a parabola (P < 0.05), suggesting that a maximum in WBPB was achieved between groups B and C. In conclusion, despite a dose response early in recovery, a periodized protein intake with multiple smaller doses after physical activity may be more beneficial than a single bolus dose in promoting daily WBPB in healthy active children.

Effect of milk consumption on rehydration in youth following exercise in the heat

Low-fat milk is thought to be an effective postexercise rehydration beverage in adults; however, little is known about milk’s rehydration ability in children after exercising in the heat. This study tested the hypothesis that because of its electrolyte and protein content, skim milk (SM) would be more effective than both water (W) and a carbohydrate/electrolyte solution (CES) in replacing body fluid losses in children following exercise in the heat. Thirty-eight (19 females) heat-acclimated pre- to early pubertal (PEP, aged 7–11 years) and mid- to late-pubertal (MLP, aged 14–17 years) children performed 3 sessions in 34.5 °C, 47.3% relative humidity, consisting of 2 × 20-min cycling bouts at 60% peak oxygen uptake followed by consumption of either W, CES, or SM. Each beverage was consumed immediately after exercise in a volume equal to 100% of their body mass loss during exercise. Urine samples were collected before, during, and after exercise, as well as the 2-h period following beverage consumption. On average, children dehydrated 1.3% ± 0.4%. Children ingested 0.40 ± 0.11 L (PEP) and 0.74 ± 0.20 L (MLP) of fluid. The fraction of the ingested beverage retained at 2 h of recovery was greater with SM (74% ± 18%) than W (47% ± 26%) and CES (59% ± 20%, p < 0.001 for both), and greater in CES than W (p < 0.001). All participants were in a hypohydrated state after 2 h of recovery, following the pattern SM < CES < W. In both PEP and MLP children, SM is more effective than W and CES at replacing fluid losses that occur during exercise in the heat.

Postexercise protein ingestion increases whole body net protein balance in healthy children

Postexercise protein ingestion increases whole body and muscle protein anabolism in adults. No study has specifically investigated the combined effects of exercise and protein ingestion on protein metabolism in healthy, physically active children. Under 24-h dietary control, 13 (seven males, six females) active children (∼ 11 yr old; 39.3 ± 5.9 kg) consumed an oral dose of [(15)N]glycine prior to performing a bout of exercise. Immediately after exercise, participants consumed isoenergetic mixed macronutrient beverages containing a variable amount of protein [0, 0.75, and 1.5 g/100 ml for control (CON), low protein (LP), and high protein (HP), respectively] according to fluid losses. Whole body nitrogen turnover (Q), protein synthesis (S), protein breakdown (B), and protein balance (WBPB) were measured throughout exercise and the early acute recovery period (9 h combined) as well as over 24 h. Postexercise protein intake from the beverage was ∼ 0.18 and ∼ 0.32 g/kg body mass for LP and HP, respectively. Q, S, and B were significantly greater (main effect time, all P < 0.001) over 9 h compared with 24 h with no differences between conditions. WBPB was also greater over 9 h compared with 24 h in all conditions (main effect time, P < 0.001). Over 9 h, WBPB was greater in HP (P < 0.05) than LP and CON with a trend (P = 0.075) toward LP being greater than CON. WBPB was positive over 9 h for all conditions but only over 24 h for HP. Postexercise protein ingestion acutely increases net protein balance in healthy children early in recovery in a dose-dependent manner with larger protein intakes (∼ 0.32 g/kg) required to sustain a net anabolic environment over an entire 24 h period.

Effects of postexercise milk consumption on whole body protein balance in youth

In adults, adding protein to a postexercise beverage increases muscle protein turnover and replenishes amino acid stores. Recent focus has shifted toward the use of bovine-based milk and milk products as potential postexercise beverages; however, little is known about how this research translates to the pediatric population. Twenty-eight (15 girls) pre- to early pubertal (PEP, 7-11 yr) and mid- to late-pubertal (MLP, 14-17 yr) children consumed an oral dose of [(15)N]glycine prior to performing 2 × 20-min cycling bouts at 60% V̇O(2 peak) in a warm environment (34.5°C, 47.3% relative humidity). Following exercise, participants consumed either water (W), a carbohydrate-electrolyte solution (CES), or skim milk (SM) in a randomized, cross-over fashion in a volume equal to 100% of their body mass loss during exercise. Whole body nitrogen turnover (Q), protein synthesis (S), protein breakdown (B), and whole body protein balance (WBPB) were measured over 16 h. Protein intake from SM was 0.40 ± 0.10 g/kg. Over 16 h, Q and S were significantly greater (P < 0.01) with SM than W and CES. B demonstrated a trend for a main effect for beverage (P = 0.063). WBPB was more negative (P < 0.01) with W and CES than with SM. In the SM trial, WBPB was positive in PEP, although it remained negative in MLP. Boys exhibited significantly more negative WBPB than girls (P < 0.05). Postexercise milk consumption enhances WBPB compared with W and CES; however, additional protein intake may be required to sustain a net anabolic environment over 16 h.

Fluid Balance and Dehydration in the Young Athlete

Many young athletes train and compete under conditions that put their body fluid balance at risk, and hypohydration is usually the major concern. Another less frequent condition is hyperhydration that—if accompanied by other risk factors—may cause hyponatremia. Water and electrolyte losses during physical activities occur primarily from sweat. Such losses have been identified mostly in active (but nonathletic) young populations under laboratory settings. Studies have been trying to estimate fluid losses in the athletic population under field conditions, taking into account the sport modality and environmental conditions. Besides these external conditions, young athletes adopt different drinking attitudes, which may depend on knowledge, education, and the opportunities to drink during the break periods as well as fluid availability. Focusing on the young athlete, this review will discuss water and sodium losses from sweat, the effects of hypohydration on performance, and fluid intake attitudes within and during practices and competitions. Some considerations related to the methods of identifying hydration status and guidelines are also given, with the understanding that they should be individually adapted for the athlete and activity. The young athlete, parents, coaches, and athletic/health professionals should be aware of such information to prevent fluid imbalances and the consequent hazardous effects on performance and health.