Q. Why is whey—particularly whey isolate—considered a fast-acting protein?
A. The concept of “fast” and “slow” acting proteins was first described in the literature by Boirie et al. in 1997. Whey, a protein derived from milk, is considered fast-acting because unlike casein, its impact on postprandial (i.e., after eating) protein metabolism is fast, high (i.e., a lot of amino acids are available immediately) and transient. The amino acids derived from whey are typically associated with protein synthesis and oxidation and not in the inhibition of protein breakdown—so it’s great for muscle building, but not so much for muscle repair. These metabolic characteristics of whey are due in part because whey is not coagulated by the gastric juices of the gut, allowing its amino acids to be assimilated into the body easily. A rapid release of amino acids in the blood from the digestion of whey allows the amino acids to be used effortlessly for muscle enhancement. This is partly because whey’s amino acid profile is very similar to that of human muscle, making it the protein of choice for bodybuilders and athletes. Whey protein isolate is the more preferred form of whey over whey protein concentrate because of the high elemental amount of protein per serving—isolates provide 90% protein per gram of product—ensuring a high concentration of protein in a small dose.
Q. Why is casein considered a slow- or extended-acting protein?
A. Casein is the dominant protein found in milk, and unlike whey, it coagulates in the stomach—the protein then curdles, causing a delay in gastric emptying (i.e., the process of stomach contents passing into the small intestines for further digestion). This means that the release of amino acids into the blood will be slower, lower (i.e., not as many amino acids are available) and prolonged compared to how whey is metabolized. Therefore, with casein supplementation, although protein synthesis is slightly increased and oxidation is moderately stimulated, protein breakdown is markedly inhibited compared to whey. Casein’s slower absorption profile seems to better promote a positive protein balance in the body, which is an essential requirement for reconstructing broken-down muscles. Therefore, casein is the preferred protein for prolonged hours of muscle rebuilding and repair and makes for a perfect partner to whey protein.
Q. What are the benefits of having both proteins in one formula?
A. As previously mentioned, the digestion, absorption and metabolic response of whey and casein differ in the body. Whey protein primarily stimulates protein synthesis for muscle enhancement, whereas casein inhibits protein breakdown, allowing run-down muscles to rebuild and repair. The speed of absorption of dietary amino acids by the gut varies according to the type of dietary protein ingested. Whey protein produces a dramatic, but short increase of plasma amino acids; whereas, casein produces a delayed plateau of moderate amino acid availability due to its slow gastric emptying. Therefore, a combination of both proteins may be most appropriate for the athletically inclined or active individual since whey will provide immediate amino acid replenishment, while the addition of casein will help prolong the extent to which amino acids are available in the body for continual muscle support.
Q. Who would most benefit from taking both proteins and why?
A. Everybody needs protein. Particular lifestyles and individuals at different life stages have special protein requirements. But, no one requires protein more than active individuals, athletes and weekend warriors who need strength, power and endurance. Since these individuals are constantly assembling, breaking down and using proteins on a daily basis, up to 35% (or 0.8 to 1.5 g/kg) of their caloric intake should come from high-quality, complete protein. Although variances and daily amounts of protein are dependent on weight and physical activity level, an ideal source of complete protein for those leading an active lifestyle is a formula that provides both fast-acting undenatured whey protein isolate and extended-acting undenatured micellar casein, like Bluebonnet’s 100% Natural Dual-Action Protein Powder.
Trisha Sugarek holds a Master’s in Nutrition from Texas Woman’s University and also a Bachelor’s of Science Degree in Nutrition and Foods from Texas State University. Ms. Sugarek is currently the National Educator as well as a Research & Development Specialist at Bluebonnet Nutrition where she investigates new ingredients, assists in the launch of new products, and provides industry training on numerous subjects as it relates to the connection between nutrition and health. She is a frequent editorial contributor and lecturer on the benefits surrounding the responsible use of supplements.
Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrere B, “Slow and Fast Dietary Proteins Differently Modulate Postprandial Protein Accretion,” Proc. Nat. Acad. Sci. USA 1997 Dec 23; 94(26), 14930–14935.
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Dangin M, Boirie Y, Guillet C, Beaufrere B, “Influence of the Protein Digestion Rate on Protein Turnover in Young and Elderly Subjects,” J. Nutr. 2002 Oct; 132 (10), 3228S–333S.
Freund HR, Hanani M, “The Metabolic Role Of Branched-Chain Amino Acids,” Nutrition. 2002 Mar; 18 (3), 287–288.
Published in WholeFoods Magazine, Aug. 2010