Dietary protein requirements and body protein metabolism in endurance-trained men

Abstract

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.

Protein and Amino Acid Needs of the Strength Athlete

“…If other amino acids follow a similar pattern, dietary amino acid needs could be substantially elevated by exercise. Although these data are consistent with several nitrogen balance studies involving high intensity exercise (34,73,83), they conflict with several others that used lower intensity exercise (17,40,85) and found that protein requirements were actually reduced following adaptation to an exercise program. Few individual amino acids have been studied to date (93), so it is not possible to make a conclusion regarding exercise effects on overall amino acid need.…”

Sports nutrition

“…Takmičari u sportovima aerobne izdržljivosti, koji izgledaju mršavo i manje mišićavo od npr. dizača tegova, zapravo imaju skoro jednako visoku potrebu za proteinima (po jedinici telesne mase) kao sportisti u sportovima snage (27,28). Preporučeni dnevni nivo unosa proteina za opštu populaciju je 12-15% od ukupnog unosa kalorija, što bi iznosilo nekih 0,8 grama proteina po kilogramu telesne mase.…”

“…Preporuke za povećanim unosom proteina kod sportista zasnivaju se na četiri faktora (29)(30)(31). Sportisti obično imaju veću bezmasnu telesnu masu, za čije je održavanje potrebno više proteina; oni putem urina gube malu količinu proteina (fenomen poznat kao proteinurija), sagorevaju malu količinu proteina za vreme fizičke aktivnosti (približno 5% od ukupnog sagorevanja energije) i potrebna im je dodatna količina proteina da bi se oporavili od oštećenja mišića koja nastaju tokom trajanja treninga.…”

Optimal Protein Intake in Athletes

“…This is postulated to be an effect of carbohydrate depletion [37]. The literature supports endurance athletes' consuming between 1.2 and 1.4 g/kg/day or 150% to 175% of the RDA [38][39][40][41][42]. It is important to note that these studies were performed using male athletes and the results may not be reproducible in females as some studies suggest that women utilize less protein than men when performing endurance exercise [21,43,44].…”