If you're a guy who lifts weights, drinking a protein shake after your workout with mostly fast-digesting protein gives your body more of a key muscle-building amino acid—leucine—than a shake with...

If you lift weights and drink a protein shake after your workout, one made only with fast-digesting whey might give your body a quicker boost of key muscle-building amino acids than a mix with mostly slow-digesting casein.

If young men who don't usually work out drink a special protein-and-sugar shake about an hour after lifting weights, their muscles build protein much faster—nearly triple the rate—compared to just working out without the shake.

If you're a guy who lifts weights, drinking a protein shake after your workout with different mixes of fast- and slow-digesting milk proteins — like whey and casein — gives you about the same muscle and strength gains, even if your body processes the amino acids differently.

Eating a big protein meal (100g) after working out keeps your blood amino acid levels high for the whole 12 hours, while a smaller meal (25g) only keeps them high for the first 5 hours.

After swimming, rats that drank whey protein had more leucine in their blood than those drinking other proteins at 1 and 1.5 hours after eating.