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Micellar Casein: The Protein With Staying Power
  Proteins, along with carbohydrate and fat, make up the main energy-providing nutrients of the diet. Proteins are unique for many reasons - they contain nitrogen, and they provide amino acids that serve as building blocks for the formation of new proteins. But not all dietary proteins are equal in their biological effects. An emerging concept in protein quality is that digestion rate has a major impact on protein effects in the body. This has led to the classification of proteins as either slow or fast. Some proteins are digested slowly, whereas others are digested quickly and results in quite different effects. Another critical factor that contributes to the quality of a protein is the method of processing. In this regard, micellar casein has several unique proteins that make it very attractive as a protein supplement for athletes. Here, the benefits of micellar casein      
are overviewed and we recount some of the key findings from studies examining the unique benefits of casein on protein balance.

Casein is the most abundant protein in milk.
Milk actually contains a variety of proteins, and due to many unique properties is easily converted to a wide range of products such as cheese and yogurt. The amino acids in caseinare present in such a ratio to promote growth and development of the young. It has all the essential amino acids, which makes it score well on all methods of protein quality. The other main protein in milk is whey. Whey protein is more soluble in an acid environment, whereas individual casein molecules are relatively insoluble in the aqueous environment of milk. Because casein is insoluble it tends to form structures called micelles. Micelles are suspensions of spherical structures that increase solubility in water. The casein micelle also contains water and a salt (usually calcium or phosphorus) in the core. Because of these unique properties, casein has a much slower digestion rate. During normal treatment of milk, which usually involves heat or acid, the casein peptides and the micelle structure become disturbed or denatured. Simple put, the proteins are disrupted and broken apart to simpler structures. As a result a gelatinous material is formed - the curd - and this is the basis for formation of products such as cheese. Micellar casein is undenatured, containing more of the intact peptides in their natural form. In order to retain an abundance of micellar protein during processing, specialized treatment of milk has to be performed. Because the casein micelle is in suspension, it can be separated from the rest of milk by centrifugation at a very high speed. One method to preserve micellar casein is ultrafiltration or microfiltration. This avoids exposing the proteins to heat, acid or other chemicals thereby preserving micellar casein. Thus, more bioactive peptides with immuno- and growth-modulating effects are present in the protein.
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Another important characteristic of micellar casein is that it is digested slowly, and therefore results in a slow but steady release of amino acids into the circulation. The effects of this pattern of slow amino acid release has been investigated in a number of studies and been shown to be quite potent at promoting an anti-catabolic environment for muscle growth (1).

A first classic study documenting the effects of micellar casein on protein metabolism was done by French researchers and published in the prestigious Proceedings of the National Academy of Sciences (2). The researchers gave healthy subjects 30 g of either whey protein or casein protein and made several measures of the anabolic and catabolic effect for 7 hours after the meal. What they found was that whey protein resulted in a rapid increase in blood amino acids and protein synthesis, but it was short-lived. Casein on the other hand resulted in a prolonged increase in blood amino acids that resulted in a 34% reduction in protein breakdown. The net protein balance remained more positive for the casein protein over a 7 hour period. The authors attributed the superior long-lasting effect of casein to a delayed gastric emptying and slower absorption rate from the gastrointestinal tract. These findings were quite revolutionary. In fact, a commentary was written in the top science journal in the world - Nature, that went on to highlight the important aspects of how various proteins have different effects on protein turnover (3).

To gain further insight into these phenomena, researchers performed additional experiments to document the effects of digestion rate of proteins on protein turnover. In the first study (4), healthy young men were provided one of four meals:
    1) a single meal composed of 30 g of casein (separated by microfiltration and ultrafiltration),

    2) a single meal containing 30 g of individual amino acids equal to the casein meal,

    3) a single meal composed of 30 g of whey protein, and

    4) 30 g of whey protein provided in a sequence of 13 small meals given each 20 min.
In this case, Meal 1 and Meal 2 were both casein, but varied in digestion rate. Meal 3 was whey protein which is a fast-digesting protein. Meal 4 was whey protein, but the repeated ingestion mimicked the characteristics of a slow digestion protein like casein. The results supported the importance of digestion rate on protein turnover. Meal 2 (free amino acids) and Meal 3 (whey protein), both fast-digesting meals, resulted in a larger increase in protein synthesis, but it was transient. They also resulted in a large transient increase in protein oxidation. Meal 1 (casein) and Meal 4 (repeated small whey protein), both slow-digesting meals, resulted in a smaller effect on protein synthesis, but prevented protein oxidation and strongly inhibited protein breakdown. Protein balance over the 7 hour period of measurements was significantly higher with the slow-digesting meals. Thus, casein or small whey protein consumed repeatedly resulted in the most favorable protein balance over a sustained period.

These studies show unequivocally that a slow-digesting protein, in these cases microfiltered and ultrafiltered micellar casein, is an independent regulator of protein retention. Therefore micellar casein makes an ideal protein supplement to sustain long periods of an anabolic environment for muscle growth. This makes micellar casein particularly attractive as protein supplement for such periods as prior to bed or any time frequent meals cannot be consumed.

1. 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-33S.
2. Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrere B. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A. 1997 Dec 23;94(26):14930-5.
3. Fruhbeck G. Protein metabolism. Slow and fast dietary proteins. Nature. 1998 Feb 26;391(6670):843, 845.
4. Dangin M, Boirie Y, Garcia-Rodenas C, Gachon P, Fauquant J, Callier P, Ballevre O, Beaufrere B.The digestion rate of protein is an independent regulating factor of postprandial protein retention. Am J Physiol Endocrinol Metab. 2001 Feb;280(2):E340-8.