In one study, researchers tested the idea that a combination of amino acid proteins from soy and dairy together would feed the body longer after exercise than whey protein alone. The 20g protein blend contained 25% isolated soy, 25% whey and 50% casein.
One hour before a high-intensity leg resistance exercise, 20 young adults took either the protein blend or whey alone.
Doctors explained that the body absorbs whey protein rapidly, casein more slowly, and soy protein somewhere in between. Researchers took thigh muscle biopsies before exercise, one to three hours after, and again three to five hours after exercise.
While the effects for whey were shorter, the soy-whey-casein blend delivered essential amino acid nourishment and promoted muscle-building activity up to five hours after exercise.