Morifuji, M., Aoyama, T., Nakata, A., Sambongi, C., Koga, J., Kurihara, K., Kanegae, M., Suzuki, K., & Higuchi, M. (2009). Effect of co-ingestion of carbohydrate and whey protein hydrolysates on exercise performance and blood biochemical parameters of carbohydrate metabolism in male athletes. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

This study compared the effect of the co-ingestion of carbohydrate and whey protein hydrolysates with carbohydrate-alone on exercise performance and post-exercise blood biochemical parameters of carbohydrate metabolism in male athletes (N = 8). Ss exercised on a cycle ergometer continuously for 60 minutes on two separate occasions at 68% VO2max, interrupted by six two-minute intervals at 88% VO2max. Ss cycled at 60% VO2max during the last 10 minutes. On one occasion, immediately after and 30, 60, 90, and 120 minutes after exercise, Ss received a supplement containing 1) 17.5 g carbohydrate, 2) 3.0 g whey protein hydrolysates and 17.5 g carbohydrate (L-WPH), or 3) 8.0 g whey protein hydrolysates and 17.5 g carbohydrate (H-WPH). On both occasions, after a two-hour recovery, a time-trial was performed. Blood samples were drawn before exercise and at 0, 30, 60, 90 and 120 minutes after the exercise, and also after the time-trial test.

The blood glucose response was lower and the plasma insulin response was significantly higher in the H-WPH group compared to the carbohydrate-alone group. The concentrations of plasma amino acid and dipeptide were also higher in both whey protein hydrolysates groups compared to the carbohydrate group. There was a strong positive correlation between the plasma concentrations of insulin and the biochemical markers of Leu, Ile, Met, Thr, Tyr, Phe, Trp, Ile-Leu and Val-Leu. Furthermore, the plasma IL-6 and free-fatty acid levels after the time-trial were significantly lower in the H-WPH group than in the carbohydrate group. The time-trial endurance performance was not statistically different between the treatments.

Implication. The co-ingestion of carbohydrate and whey protein hydrolysates was more effective than ingestion of carbohydrate alone for stimulating insulin secretion and plasma amino acid and dipeptide availability in exercise-trained athletes. Furthermore, blood parameters of substrate metabolism, such as free-fatty acids and IL-6 also changed after co-ingestion of carbohydrate and whey protein hydrolysates. The ingestion of carbohydrate with whey protein hydrolysates has a beneficial role of increasing post-exercise glycogen repletion rates but does not translate into any obvious performance improvements. [This is another instance of where significant biochemical/physiological changes occur but are not accompanied by significant performance alterations. It is dangerous to infer that theoretical physiology, of which this is an example, has a direct correlate with performance improvement.]

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