Whey Protein vs Casein Protein

Whey and casein are two of the most popular protein supplements on the market, and for good reason. They’re both high-quality, highly bioavailable, complete proteins that are rich in branched-chain amino acids (BCAAs). This quality makes them perfect for muscle growth and repair.

However, despite both coming from milk, there are distinct differences between these muscle-building brothers.

Whey and casein are dairy proteins found in milk – casein is the “curds” in “curds and whey” (think: cottage cheese). Whey is considered a “fast” protein, because it is rapidly digested in as little as an hour, whereas casein is a “slow” protein that is digested over several hours. Most food sources of protein are also “slow” proteins (eg, eggs, steak, fish), especially when consumed with mixed meals. Soy is a plant-based protein source that is found naturally in soybeans, edamame, and tofu.

There are a few questions to be answered regarding the effects of protein supplementation on strength and body composition. Is there a difference between any of these proteins? Or is it simply an issue of quantity over quality?

We can address these questions from two angles: (1) the short-term effects of different proteins on muscle building and/or the prevention of muscle breakdown and (2) the long-term effects on muscle size and strength.

The former was discussed at length in this article: Is Hydrolyzed Protein Better Than Whey? As a brief refresher, whey protein, regardless of whether it is hydrolyzed or intact, is superior to casein and soy in the short-term… but that doesn’t always guarantee that choosing whey over casein or soy will make you bigger stronger faster. For that, we have to look at the long-term studies.

Whey stimulates protein synthesis

Fast-digesting whey means it is emptied from the stomach quickly, resulting in a rapid and large increase in plasma amino acids. This translates into a quick but transient increase in protein synthesis, while protein breakdown is not affected. Whey also has higher levels of leucine, a potent amino acid that stimulates protein synthesis. Whey protein is superior at augmenting protein synthesis rapidly, but this positive effect is short-lived. Consuming repeated doses of whey allows for sustained high levels of blood amino acids and repeated bursts of protein synthesis that provide superior effects on muscle protein balance.

Casein offers a positive protein balance

Casein is the most abundant protein in milk. It is relatively insoluble and tends to form structures called micelles that increase solubility in water. During the processing of milk, which usually involves heat or acid, the casein peptides and micelle structure become disturbed or denatured to form simpler structures. As a result, a gelatinous material is formed. This is the basis for why casein has a slower rate of digestion, and results in a slow but steady release of amino acids into circulation.