A Whey-Supplemented, High-Protein Diet versus a High-Carbohydrate Diet: Effects on Endurance Cycling Performance

This study compared a training diet recommended for endurance athletes (H-CHO) with an isoenergetic high protein (whey supplemented), moderate carbohydrate (H-Pro) diet on endurance cycling performance. Over two separate 7-d periods subjects (n = 7) ingested either H-CHO (7.9 +/- 1.9 g x kg(-1) x d(-1) carbohydrate; 1.2 +/- 0.3 g x kg(-1) x d(-1) fat; 1.3 +/- 0.4 g x kg(-1) x d(-1) protein) or H-Pro (4.9 +/- 1.8 g x kg(-1) x d(-1); 1.3 +/- 0.3 g x kg(-1) x d(-1); 3.3 +/- 0.4 g x kg(-1) x d(-1)) diet in a randomized, balanced order. On day 8 subjects cycled (self-paced) for a body weight dependent (60 kJ/bm) amount of work. No differences occurred between energy intake (P = 0.422) or fat intake (P = 0.390) during the two dietary conditions. Performance was significantly (P = 0.010) impaired following H-Pro (153 +/- 36) compared with H-CHO (127 +/- 34 min). No differences between treatments were observed for physiological measures taken during the performance trials. These results indicate an ergolytic effect of a 7-d high protein diet on self-paced endurance cycling performance.