When older women drink whey protein shakes, their muscles start repairing and growing faster—especially if they also do leg exercises—while collagen protein shakes don’t do much unless they exercise, and even then, it’s much weaker.

After drinking whey protein shakes every day for a week, older women’s muscles kept building up new protein even on days they didn’t exercise—collagen protein didn’t do this at all.

Even though whey protein made muscles build faster, it didn’t change the usual ‘on/off’ switches in muscle cells that are supposed to control growth—suggesting other mechanisms are at play.

When rats exercised and then ate a small amount of whey protein hydrolysate, their muscles built protein faster than when they ate regular whey protein at the same dose.

One scoop of whey protein has over five times more of the key muscle-building amino acid (leucine) than one scoop of collagen protein—even though both have the same total protein.

Even though both protein shakes had the same amount of protein, the whey one made the key muscle-building amino acid (leucine) in the blood much higher than the collagen one.