Neither type of whey protein affected insulin levels in rats' blood an hour after exercise, regardless of dose.

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.

When rats ate a larger dose of regular whey protein, their blood had more leucine than when they ate the same amount of hydrolyzed whey protein an hour later.

A small dose of whey protein hydrolysate made a key muscle-building signal stronger in rats than regular whey protein or no protein.

A larger dose of regular whey protein activated a key muscle-building pathway more than hydrolyzed whey protein or no protein in rats.

If you're overweight, eating a lot more protein — especially from whey — for a month won't help your body use insulin better unless you're also losing weight.