Loss of muscle mass with age (sarcopenia) may be caused by a reduction of muscle protein synthetic response to food intake. A group of researchers set out to find which milk protein was the best for muscle protein accretion, and would therefore help stave off sarcopenia.
Three groups of older men were fed a meal-like amount of whey, casein, and casein hydrolysate proteins. Their protein ingestion was combined with an intravenous tracer which was used to assess digestion and absorption kinetics, and their muscle synthesis rates were also calculated from the ingested tracer.
According to the study in the American Journal of Clinical Nutrition:
"Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. This effect is attributed to a combination of whey's faster digestion and absorption kinetics and higher leucine content."