Soy Protein Pumps You Up

Researchers at Indiana Universitys School of MedicineEvansville have found that soy protein and whey protein equivalently promote muscle protein synthesis, disproving a popular myth that athletes should avoid soy because its protein is inferior to other sources.

The study (Feeding Meals Containing Soy or Whey Protein after Exercise Stimulates Protein Synthesis and Translation Initiation in the Skeletal Muscle of Male Rats, Tracy G. Anthony, et al, J. Nutr. 137:357-362, Feb. 2007) compared the early response of skeletal-muscle protein synthesis and translation initiation after eating different protein sources following endurance exercise (120 minutes of treadmill exercise) in male rats. One hour after eating a carbohydrate-only, carbohydrate and whey protein, or carbohydrate and soy protein meal, 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 that a meal of carbohydrates only produced an inferior synthesis. 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.

Soy and whey proteins actually complement each other well when used in an exercise regimen, said Greg Paul, Ph.D., one of the studys researchers and the global director of nutrition strategy, The Solae Company, St. Louis. Whey protein is high in branched-chain amino acids, while soy protein has high amounts of the amino acids arginine and glutamine.

Paul also theorizes that athletes who use both soy and whey protein 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, so combining the two might provide a more-prolonged, deliberate release of amino acids to key muscle groups.