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Many new protein supplements are profoundly different than their predecessors. This revolution came about when a French study found that casein - a protein found in milk - prolonged digestion
and absorption of amino acids (Y. Boirie et al., "Slow and fast dietary proteins differently modulate postprandial protein accretion," Proceedings of the National Academy of Science USA,
94:14930-5,1997). Further, slowing the digestive process caused a much greater anticatabolic response than that induced by whey protein alone, which is digested and absorbed quickly. When
whey and casein are combined, then, consumers can reap the benefits of both proteins. Almost immediately after this study was published, mixing casein and whey became the "cutting edge" in
Not all casein is equivalent. The type utilized in the French study was micellar casein, which is isolated from milk by filtration, rather than by use of acid or heat. The filtration method preserves the structural integrity of the protein, unlike what occurs in other processing methods.
The crux of the issue lies in the micelle itself. Its unique spherical structure allows casein to remain suspended in milk, which produces milk's characteristic opaque appearance. Basically, when heat or acid is used to separate casein out of milk, the micelle's structures are altered, resulting in a loss of biological activity and digestibility.
Milk and its intact undamaged protein fractions - of which micellar casein is one - were designed by Mother Nature to be digested and absorbed by humans; milk's function is to nourish offspring. It's not surprising, then, that undamaged milk protein provides us with more than just a source of amino acids. It also provides us with many biologically active proteins that have direct immune and physiological benefits that aren't provided by tissue and vegetable proteins. These other proteins we eat aren't first and foremost meant to nourish; instead, they are contractile (muscles contract) or structural (contribute to the shape/structure of a plant) proteins. The fact that we can digest these types of proteins makes living a whole lot easier, but that's only because we have adapted to utilizing them.
To maintain the spectrum of biological functions of milk protein, the casein units must be as undamaged as possible. This is the critical difference between micellar casein and other forms, such as caseinate.
Caseinate is typically produced by first precipitating casein using acid or heat. Casein, which does not dissolve in water, is made more soluble by forcing it to react with a strong inorganic base like calcium hydroxide. Caseinate does possess a casein amino-acid profile, but its micelles are damaged. Not only are digestibility and production of biologically active digestive fractions adversely altered, but caseinates are also stripped of naturally occurring chelated minerals.
How can you tell which kind of casein you're getting? Micellar casein appears on ingredients labels as milk protein concentrate, but that category also contains total milk proteins that are not processed as gently. Caseinates are listed by name, but there are many grades of caseinate. Those with increased viscosity will slow digestion, but the biologically active peptide content may still be compromised. Ultimately, cost is the single best indicator of what you are getting. High-quality components like micellar casein and viscous caseinates add to the bottom line.