Researchers from Indiana University's School of Medicine - Evansville and collaborators from State University of New York - Stony Brook and the Solae Company looked at the effect of different protein sources on skeletal muscle protein synthesis in rats after endurance exercise.
"Taken in total, our study suggests both soy and whey 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.
"In conclusion, general protein synthesis and the mRNA cap binding step are promoted comparably by soy protein and whey protein in the skeletal muscle of exercised rats," said the researchers.
Co-author of the study, Greg Paul, global director of nutrition strategy at The Solae Company, said that the soy and whey proteins could actually complement each other well when used in an exercise regimen.
"Whey protein is high in branched chain amino acids, while soy protein has high amounts of the amino acids arginine and glutamine," he said.
Paul said that incorporation of both soy and whey protein into an athlete's diet may benefit from their different rates of digestion and amino acid absorption. Whey protein digests more quickly in the body, he said, while soy protein digests more gradually, giving a prolonged, deliberate release of amino acids to key muscle groups.
Source: Journal of Nutrition Volume 137, Pages 357-362 "Feeding Meals Containing Soy or Whey Protein after Exercise Stimulates Protein Synthesis and Translation Initiation in the Skeletal Muscle of Male Rats" Authors: T.G. Anthony, B.J. McDaniel, P. Knoll, P. Bunpo, G.L. Paul, and M.A. McNurlan