Milk protein is 80% casein and 20% whey, and is our favorite source of casein and the #1 ingredient of SELECT Protein.
With Milk Protein Isolate, we've trimmed down the fat and carbohydrate content from milk, leaving you with the 20/80 whey-casein protein ratio and synergistic growth factors intact. Indeed, MPI may be the single best protein source money can buy. To quote "The Protein Book":
"[R]esearch seems to suggest that consuming slower digesting proteins, or a mixture of fast and slow proteins during the post-training period may provide superior results compared to a fast protein... [M]ilk protein isolate (MPI), which contains 20% whey and 80% casein might turn out to be an ideal post-workout protein[...] By providing a rapidly available source of amino acids (from the whey) with a slower digesting source (from the casein), both protein synthesis and breakdown should be positively affected"