Long-term feeding of whey protein hydrolysates increases skeletal muscle glycogen levels and improves exercise performance in mice

Background

Recently, our studies have shown that co-ingestion of carbohydrate and whey protein hydrolysate (WPH) is more effective for increasing post-exercise skeletal muscle glycogen content than ingestion of other protein sources (whey protein, casein hydrolysate, or branched chain amino acids). We have also shown that chronic feeding of whey protein increases glycogen contents in skeletal muscle of exercise-trained rats to a greater extent than does casein. To confirm our hypothesis that long-term feeding of WPH is more effective for increasing both muscle glycogen content and exercise performance than other protein sources, we compared long-term feeding of WPH to other protein sources for their effects on skeletal muscle glycogen levels and exercise performance.

Methods

Male ddY mice were divided into three groups and allowed free access to water and diet containing either whey protein, WPH, or casein for five weeks. During this period, the mice were exercised in a pool five times a week, with exercise performance being measured once a week. On the final day of the five week experiment, the mice were killed for analysis of glycogen content in the gastrocnemius muscle.

Results

The WPH group showed a significant increase (p < 0.05) in exercise performance (42.35+/-5.11 min) compared with the casein group (28.47+/-1.96 min). Furthermore, skeletal muscle glycogen levels were higher in the WPH group (4.42+/-0.24 mg/g) than in either the whey protein (3.39+/-0.40 mg/g, p < 0.05) or casein group (2.60+/-0.18 mg/g, p< 0.01).

Conclusion

These results indicate that long-term feeding of WPH is more effective for increasing glycogen content in skeletal muscle, and improving exercise performance than other protein sources.