Effect of Chronic Endurance Exercise on Retention of Dietary Protein

Abstract

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.

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.…”

Level of dietary protein impacts whole body protein turnover in trained males at rest

“…Although some studies have found optimal protein intakes to be 1.0 to 1.8 g/kg of body weight for endurance-exercising individuals [8,9,11,13,21], there are studies that oppose this view and hypothesize that with the maintenance of energy balance, protein intake of 0.8 g/kg of body weight is sufficient for this population [1,6].…”

“…With increasing dietary protein there is an increase in nitrogen retention [8][9][10][11], an increase in the oxidation of leucine [2], and changes in rates of protein turnover [9,10]. Although the implications of noted changes in rates of protein turnover in response to protein intake are not fully understood, it is clear that increases in dietary protein influence rates of protein turnover [2,10].…”

Nutritional Considerations for Ultraendurance Performance

“…Ultraendurance athletes consume 1.5 to 2.0 g protein kg-' (6,21), meeting or exceeding the recommendations made by various researchers (16,24). However, female ultraendurance athletes with low caloric intakes may take in less than optimal amounts of protein in an effort to consume adequate dietary carbohydrate.…”