Protein from soy or from whey is equally effective for synthesis of muscle protein after endurance training, suggests an animal study that may challenge the perception that athletes should avoid soy if reproducible in humans. "Taken in total, our study suggests both and proteins are useful sources of protein for muscle support following aerobic exercise," wrote lead author Tracie Anthony in the Journal of Nutrition. The researchers divided treadmill-acclimated rats to either a control group (no exercise) or the exercise group.
The exercise group was further divided into three groups and fed a meal containing carbohydrates only, carbohydrate plus soy protein, or carbohydrate plus whey protein. Before eating the experimental meals the rats were exercised for two hours at a speed of about 26 metres per minute. One hour after exercise, the researchers measured serum insulin concentrations and serum branched-chain amino acid concentrations, as well as levels of the marker for muscle protein synthesis, the mRNA cap binding complex eIF4F.
Anthony and her colleagues report that, compared to the non-exercising control rats, serum insulin levels were higher in all of the exercise rats, while branched-chain amino acid concentrations were significantly higher in the two protein-fed groups than in the carbohydrate-only group. Serum levels of the amino-acids leucine and isoleucine were found to be higher in the whey protein-fed group than the soy protein-fed group. Both protein sources also increased formation of the mRNA cap binding complex eIF4F, said the researchers, suggesting both protein sources were effective for synthesis of muscle protein after endurance training.
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