A study from the University of Auckland in New Zealand showed that taking whey protein leads to more prolonged muscle protein synthesis than taking soy protein.
As part of the study, researchers gave older men, aged 60-75, 30 grams of either soy or whey protein and measured a marker of muscle protein synthesis (P70S6 kinase) from a muscle biopsy. Protein synthesis increased for two hours after taking soy protein but continued for another four hours after taking the whey protein.
Decreased muscle mass in older people (called sarcopenia) is a serious medical problem that results in decreased bone mass, loss of mobility, premature death, and poor blood sugar metabolism. A daily supplement of 30 grams of whey protein can encourage muscle protein synthesis in older people and could even prevent sarcopenia.