Casein protein is a slow digesting and extremely rich protein source that is a continual muscle feeder long after whey protein has run its course. Casein protein, the predominant protein found in milk, is a slow digesting protein that plays a large role in preventing muscle breakdown. Casein protein has also been shown to have the ability to slowly release amino acids which in turn causes a timed release trickle of amino acids into the bloodstream. This release can last up to 7 hours after ingestion.
Meal replacements, in the form of a powder shake and a snack bar, each providing 900 kJ, have been used successfully in several weight-loss trials (5–8). Previous trials with these kinds of meal replacements have nearly always incorporated professional dietary input from either a dietitian, a physician, or a nurse, in addition to written information supplied with the meal replacements. However, daily intake of meal replacement products by a consumer would mostly occur without professional input and feedback. One uncontrolled 12-wk study (9) evaluated meal replacements in a nonclinical worksite weight-reduction program and showed them to be effective in achieving weight loss in this environment.
Whey protein isolate is the highest yield of protein currently available, and it comes from milk. Because of its chemical properties, whey protein is the easiest to absorb into your muscles. Obviously, with its high concentration, whey protein isolate is the best to use.
Whey protein isolate is also the most pure and concentrated form of whey protein available. It contains 90% or more protein and very little (if any) fat and lactose.