The fact that athletes favor protein in their diet is hardly big news. Simple logic suggests that if muscles are made of protein, you need plenty of protein in your diet in order to build muscle mass (coupled with exercise, of course). So, most athletes make a point of ensuring that they meet their daily needs.
And while it’s true that protein can be obtained from a wide range of both plant and animal sources, it’s important to provide your body with a steady dose of complete protein – that is, the right balance of all the essential amino acids (building blocks) that your body can’t manufacture on its own.
All animal sources of protein are naturally complete, and even vegans can obtain the right amino acid balance by carefully combining plant-based protein sources (such as beans and grains) over the course of the day. But milk-based proteins are concentrated sources of certain amino acids that may offer advantages over other proteins when it comes to muscle repair and growth.
Here’s why. The two primary proteins in milk are whey and casein. Whey protein is considered a “fast” protein because it is readily digested, only taking about 15 minutes before its amino acids are detectable in your bloodstream. Casein, on the other hand, takes longer to digest. But its “slow” nature means that casein provides a more sustained release of amino acids into your system.
This is important, because your body is constantly building up and breaking down protein all day long. These two opposing processes are generally kept in balance, though. Whenever you eat protein, it stimulates protein synthesis for a few hours afterwards, and as long as your body has a sustained source of available amino acids, the natural process of protein breakdown is kept in check.
And that’s why the combination of whey and casein is considered a “one-two punch” when it comes to muscle building: the fast-acting whey protein helps stimulate muscle protein buildup, while the sustained action of casein helps inhibit the breakdown process.
But there’s an additional twist to this story, and it has to do with the unique nature of whey protein.
Whey is one of the richest sources of a group of amino acids called branched-chain amino acids (or BCAAs, in reference to their chemical structure). One feature of BCAAs is that they are the only amino acids that muscles can utilize directly for energy. And one BCAA in particular – leucine – does even more. Leucine behaves almost like a hormone in your body by stimulating certain metabolic pathways that lead to muscle protein synthesis. And whey protein contains more than twice the leucine of any other animal sources of protein.
The timing of protein intake is important too. Since muscle protein synthesis is stimulated every time you eat protein, it’s best to spread your protein intake throughout the day over all your meals and snacks.
Before exercise, a light, easy to digest meal that contains both whey protein and carbohydrates (like a protein shake) can help in a couple of ways. Carbohydrates provide quick available energy, while whey protein helps protect muscle protein breakdown. And keep in mind that protein synthesis occurs around the clock. Giving your body a hit of dairy protein before bed can help tip you into positive protein balance – even when you’re sleeping.