Drinking a beverage made from a blend of soy and dairy proteins after exercise can increase muscle growth, according to a study now online in the Journal of Nutrition. The study is the first to look at the effects of this combination of proteins on muscle protein synthesis.
University of Texas Medical Branch at Galveston researchers worked with human subjects who drank a protein blend of soy, whey and casein (a protein derived from milk) after performing resistance exercise. The three protein sources have complementary amino-acid profiles since they are digested at different rates. Results showed a more prolonged delivery of amino acids to muscles and extended muscle protein synthesis when subjects consumed the blend compared to a single source of protein alone.
“Sources of high-quality protein each have individual characteristics thought to offer unique advantages for muscle growth,” said Blake Rasmussen, interim chairman of the Department of Nutrition and Metabolism at UTMB and principal investigator of the study. “This is the first study to test the effects of combining soy with the dairy proteins whey and casein for promotion of lean body mass gain.”
Researchers based the composition of the protein blend on results from a recent pre-clinical study that demonstrated enhanced muscle protein synthesis in rats compared to another blend of soy or whey protein sources alone. The new human study used a blend of 25 percent isolated soy protein, 25 percent isolated whey protein and 50 percent caseinate.
This blend stimulated muscle growth to a similar extent as whey protein by elevating muscle protein synthesis and muscle cell growth signaling. The blend, however, increased the subjects’ anabolic window, extending the higher rate of muscle protein synthesis longer than whey alone.
The beverages provided approximately 20 grams of protein from either the soy-dairy blend or whey protein containing similar amounts of leucine, a key amino acid involved in regulating muscle protein synthesis rates. The volunteers consumed the beverages following high-intensity leg resistance exercise. Researchers collected multiple leg muscle samples from each subject to determine changes in muscle protein synthesis over time (at rest and three and five hours after exercise).
“Previous research examined only single sources of proteins and did not match the protein sources for leucine content, which is thought to trigger muscle protein synthesis,” said Paul Reidy, a graduate student in Rasmussen’s lab and first author on the study. “The extension of the anabolic window may also be important for the aging muscle.”
Nineteen healthy young adults participated in the randomized, double-blind trial. The study was funded by DuPont Nutrition & Health, makers of the soy ingredient included in the protein blend studied.
The University of Texas Medical Branch