proteins are comprised of individual ammino acids bound together forming peptides. the individual sequence and assortment of the amino acids determine the characteristics and properties of the proteins themselves.

when we ingest proteins, the peptide chain is too loarge to be absorbed and enter the blood stream. imagine a beaded necklace (with small beads) and a large sifter (with holes large enough for the individual beads to pas thru). the necklace would represent the peptide chain, the individual beads representing the amino acids making up the chain, and the sifter would represent the intestinal membrane. if you dropped that necklace into the sifter, would the beads fall thru? nope, because the chain is too complex. in order for it to pass thru, the beads would need to be separated from one another. the same is true when ingesting proteins.

the more complex that peptide chain is, the longer it takes for the enzymes to dismantle it. a similar analogy would be the difference between simple and complex carbs. because the simple sugars can be rapidly absorbed, they contribute to a rapid rise in blood glucose levels. complex carbs on the otherhand take a bit more time to breakdown and absorbed more gradually that they sort of trickle into the blood stream, which contributes to an overall constant level of blood glucose. the same is true with some proteins. whey protein has a very short peptide chain and, therefore, is broken down and absorbed into the blood stream more rapidly. whereas, casein consists of a much longer peptide chain. as a result - like complex carbs - casein takes much longer to breakdown and enter the blood stream and, therefore, contributes to a more gradual increase in and longer lasting blood protein levels.

where casein would be most beneficial would be during the day when activity level is not too high, or an hour or so before strenuous exercise. another time would be at night before bed. by maintaining a more constant level of blood proteins, especially when carbs are restricted and glucose levels are limited, these blood proteins can be made available for gluconeogenesis (making of new glucose) while preserving lean tissue.