Casein, often called micellar casein is the protein components in milk curds and is naturally the main protein in cheese. It is a popular protein supplement and complements those other milk derived proteins found in whey. The main difference between the two types is that casein is much more slowly digested and absorbed by the body whereas whey proteins have a faster absorption.
Milk is consumed at bedtime because casein helps us sleep. The slow digestion of protein coupled with the release of melatonin like peptides is shown to help with sending us off to sleep. It’s the basis behind many of the claims made for malted drinks like Horlicks or Milo for example.
Body building dietary supplements often contain a mix of blended proteins including whey and casein because they extend the digestion period and the release of peptides and amino-acids for absorption. Casein is ideal for providing nutrition when the body is resting or recovering or where targeted muscle building is required. Some established sport protein supplements rely on a balanced blend to achieve a strong absorption level: consider JYM Supplement Science’s PRO JYM blend as a good example.
Micellar casein refers to the physical structure of casein in solution. Casein is not readily soluble in water and is usually a suspension in milk. This level of insolubility increases when it is combined with acidic liquids, such as stomach acid. This is the property that results in its slow absorption because it forms a gel that is gradually digested over a 7-8 hour period.