A first-of-its kind study in the February issue of the Journal of Nutrition concludes soy protein and whey protein are equally beneficial in promoting muscle protein synthesis, dispelling a popular but unsubstantiated weight room myth that athletes should avoid soy.
Researchers at Indiana University’s School of Medicine - Evansville compared the early response of skeletal muscle protein synthesis and translation initiation following the ingestion of different protein sources after endurance exercise in rats.
The animals were subjected to 120 minutes of treadmill exercise and then fed a carbohydrate-only, carbohydrate and whey protein, or carbohydrate and soy protein meal. One hour later, researchers measured the degree of muscle protein synthesis in each rat and compared their findings to a control group.
The researchers found soy and whey proteins were equally effective at promoting general protein synthesis in the rats’ skeletal muscle, and markedly inferior synthesis was associated with the carbohydrate-only meal.
Many male exercisers avoid soy protein despite its association with myriad health benefits, including lowered cholesterol and a reduced risk of certain types of cancer. This is partly due to a common but untested notion that soy is inferior to whey protein in promoting muscle weight gain and muscle recovery.
“Taken in total, our study suggests both soy and whey proteins are useful sources of protein for muscle support following aerobic exercise,” the researchers wrote.
These findings support a growing body of evidence suggesting soy protein is as effective, and sometimes more effective, than dairy protein in terms of its ability to promote gains in lean muscle mass and facilitate muscle recovery after exercise.
“Soy and whey proteins actually complement each other well when used in an exercise regimen,” said Greg Paul, Ph.D., a nutritionist and global director of nutrition strategy at The Solae Company. “Whey protein is high in branched chain amino acids, while soy protein has high amounts of the amino acids arginine and glutamine.”
Dr. Paul also suspects athletes who incorporate both soy and whey protein in their nutritional regimens may benefit from their different rates of digestion and amino acid absorption. Whey protein digests more quickly in the body, while soy protein digests more gradually. Together, they may provide a more prolonged, deliberate release of amino acids to key muscle groups.
For more information, see: Tracy G. Anthony, Brent J. McDaniel, Peter Knoll, Piyawan Bunpo, Greg L. Paul, and Margaret A. McNurlan. Feeding Meals Containing Soy or Whey Protein after Exercise Stimulates Protein Synthesis and Translation Initiation in the Skeletal Muscle of Male Rats. J. Nutr. 2007 137: 357-362.
Editor’s Note
Resistance exercise - also called strength training - increases muscle strength and mass, but also disrupts the body’s net muscle protein balance for up to 24 hours following exercise. Skeletal muscle growth is possible only when muscle protein synthesis exceeds muscle protein breakdown.