The following is an excellent reference in summary, which I copied from the following site: http://www.betterbodz.com/proteinfinal.html (Find out more about Betterbodz at email@example.com, or call 800/335-6740. Copyright © 1995,1996,1997,1998 Betterbodz.com All Rights Reserved. )
Intact Protein Isolates are normally about 90% pure protein. Generally, they have properties that are very similar to protein concentrates with the exception that they are inherently more pure. In other words, protein isolates are better manufactured, more expensive protein sources.
Whey is by far the best selling form of protein in the marketplace today. Whey is one of the two ingredients that is separated from milk (casein is the other). Now, before going any further remember that a protein like whey can either be a concentrate (about 80% protein) or an isolate (about 90% protein). So 20 grams of whey concentrate will yield about 16 grams of pure protein while 20 grams of whey isolate will yield a more respectable 18 grams of protein. Whey has become the best selling protein product in the marketplace. Certainly it is a decent choice for protein gourmets, however, it lacks many of the highly desirable properties that soy protein possesses, especially for women.
Soy is an ingredient that comes from the soybean. First, soy is extremely rich in the muscle critical five amino acid cluster (the 3 branched chain aminos, glutamine and arginine) that will help to develop lean tissue. In fact, nearly 35% of soy protein is made up of these aminos as compared to 18% in whey protein or 16% in beef. Second, soy protein can be a key to increasing health as it is extremely rich in phytoestrogens and isoflavones. Third, soy is highly digestable and scores a perfect 1.0 in scienceís best, current protein quality standard test known as the Protein Digestability Corrected Amino Acid Score (PDCAAS).
Casein: The real knock against casein is that natural casein sources tend to contain moderate to high levels of the milk sugar lactose. Although this isnít necessarily a terrible thing, many people are lactose intolerant or suffer from digestive irregularities if they eat products containing too much lactose. Again, casein is not a bad choice for protein but is not nearly as good for women as is soy. Casein was the “other” component produced from milk in the cheese making process. In fact, casein is really just cottage cheese with a higher amount of the milk sugar lactose and the mineral calcium.
Egg Protein: decades egg was judged to be the single most superior source of protein. For use as a powdered protein supplement, compared to other sources such as soy, casein or whey, eggs isolates taste terrible, are absurdly expensive and donít offer the functional body shaping value that the other products possess.
REMEMBER: I have summarized and “cut” this article. Please see the reference above to read all about proteins.