Sometimes it seems like the diet and fitness world has gone protein crazy. Diet books tell you to eat all the bacon you want as long as you don't touch bread, and health clubs push giant tubs of mysterious powders that promise to build muscle. While much of the hoopla surrounding protein is exaggerated, protein supplementation remains a popular part of muscle-building fitness plans. Weight room debates endlessly argue the merits of one protein over another, with whey and casein usually the most-mentioned. With all this debate, you would be surprised to learn that whey and casein come from the same place -- milk.
Curds and Whey
To understand the difference between casein and whey, think of cottage cheese. Like little Miss Muffet's breakfast, cottage cheese is a combination of curds and whey. The liquid is whey, which is the portion of the milk that doesn't curdle with the addition of acid. The solid pieces, or curds, contain casein. Whey and casein are categories of protein, each containing several individual proteins. All of these proteins are responsible for different things in your body.
Whey proteins include antibodies called immunoglobulins, as well as hormones, growth factors and chemicals that help transport nutrients throughout your body. Casein proteins contain just the right mix of amino acids to promote growth, which is why mother's milk is so important for young mammals. Both types of protein are important for the body, especially if you are undergoing resistance training in an effort to build muscle. Protein supplementation can help prevent the breakdown of muscle tissue while stimulating muscle repair and growth.
Whey and casein are different, but that's not to say that one is better than the other. Whey protein digests faster, providing a quick, high peak in blood amino acids. This makes it useful as a pre-workout shake to kick start protein synthesis, which aids in muscle repair. Casein protein digests more slowly, providing more of an extended-release effect, resulting in a slow, gradual rise in amino acid levels. This helps prevent muscle breakdown during endurance exercise.
Instead of choosing one or the other, use casein and whey together for best results. This way, a single beverage -- milk -- both prevents muscle breakdown and stimulates muscle repair. Some bodybuilders swear by a glass of chocolate milk as a post-workout recovery drink for that very reason. Because whey and casein come from animal milk, they are not suitable for vegans -- soy protein and hemp protein can help fill in the gaps, and a balanced diet with adequate whole food protein may even preclude the need for a protein supplement.
- Metabolism; The Effect of Resistance Training Combined with Timed Ingestion of Protein on Muscle Fiber Size and Muscle Strength; Andersen LL, et al.
- Amino Acids; Effects of Resistance Training and Protein Plus Amino Acid Supplementation on Muscle Anabolism, Mass and Strength; Willoughby DS, et al.
- Proceedings of the National Academy of Sciences of the United States of America; Slow and Fast Dietary Proteins Differently Modulate Postprandial Protein Accretion; Boirie Y, et al.
- American Journal of Physiology -- Endocrinology and Metabolism; The Digestion Rate of Protein is an Independant Regulating Factor of Postprandial Protein Retention; Dangin M, et al.