If healthy guys drink more casein protein, more amino acids show up in their blood overall—even though a smaller percentage gets absorbed—probably because their bodies haven’t finished digesting it within 5 hours.

If a young guy drinks a protein shake with a mix of whey and casein, his body absorbs the important amino acids about as well as with pure whey—and better than with pure casein—over the next 6 hours.

If you're someone who works out regularly, adding 54 grams of casein protein to your daily diet—whether in the morning or at night—won’t make you gain fat over 8 weeks, even if you don’t change your exercise routine.

For healthy guys, drinking regular milk protein gives your body more usable protein building blocks over 5 hours than taking just whey or just casein alone.

When healthy guys drink more whey protein, their bodies absorb more of an important amino acid called phenylalanine—about 10% more when they take a higher dose.

When healthy guys drink milk protein, about half of the protein gets into their bloodstream within 5 hours — that's what muscles can use. The rest is either still being digested or gets used by organs like the liver before it ever reaches the rest of the body.