What you scarf post-workout matters for building and repairing muscle. And while scientists have long known that protein should be a key component of whatever you consume to get the job done, two new studies in the American Journal of Clinical Nutrition reveal one reason whywhey protein stands above all others: It’s the leucine.
“Whey is a high-quality milk protein that’s a rich source of the essential amino acid leucine,” says Stefan Pasiakos, Ph.D., a physiologist with the U.S. Army Research Institute of Environmental Medicine. And consuming lots of leucine leads to greater muscle protein synthesis—the intricate process that helps promote the remodeling, repair, and muscle growth that occurs after exercise, the study explains.
More from MensHealth.com: The Truth About Protein
In Pasiakos’ study, military members rode stationary bikes for 60 minutes at a moderate intensity on two separate occasions. Both times they chugged a beverage with equal amounts of protein, but one drink contained 1.9 grams of leucine, while the other packed 3.5 grams. (For reference: 10 grams of regular whey protein contains about 1 gram of leucine.) Researchers found protein synthesis was 33 percent higher after the larger leucine dose. “Leucine can help trigger complex signaling networks within muscles that turn on muscle protein synthesis,” Pasiakos says.
Meanwhile, the second American Journal of Clinical Nutrition study found that consuming 25 grams of whey protein that contained 3.5 grams of leucine after a resistance training workout led to higher blood concentrations of amino acids, including leucine, than when participants downed smaller repeat doses of whey meant to mimic another type of protein called casein. The reason? Whey is digested quickly, and makes essential amino acids available sooner—leading to a greater muscle protein synthesis response, Pasiakos says.