On Protein Types
In supplementary form, protein powders are going to be either milk-derived (mostly cow, though goat is available too), egg-derived, or soy derived. All are "complete" proteins (ie., they have all of the essential amino acids--the ones that the body cannot make on its own).
Milk Proteins: These would be whey and casein. Whey is a by-product of the cheesemaking industry--it's the liquid part of the milk (the whole "curds and whey" deal). It is a very quickly digested protein. This makes it ideal for taking in the morning, as well as post-workout. Casein, OTOH, is the opposite--ie., it is very slowly digested. It actually gels in the gut, releasing amino acids over a period of several hours.
Whey can come in a concentrate, an isolate, or a hydrolyzed form. Concentrates and isolates are the most common. Hydrolyzed proteins are almost never used on their own due to taste issues--they must be blended with other forms. Concentrates contain sub-fractions which aid in muscle-building, wound-healing, etc. However, they also typically have more fat and lactose. Isolates are lower on the fat and lactose, but don't always have those subfractions intact. As far as isolates go, micro cross-filtered is superior to ion-exchange. Ion-exchange destroys those subfractions.
Egg Protein: This is simply the protein from egg whites, and hence is free of cholesterol. Egg protein is excellent, especially for those with allergies to dairy, but it has a funky aftertaste.
Soy Protein: For those who are allergic to both Milk proteins and Egg protein, this is the only alternative, supplement-wise. It is also a standard for vegans, who refuse to consume animal products. Although it is a complete protein, its amino acid profile is inferior to the animal-derived ones. Milk and Egg protein consistently rate higher on the various protein scales--the Biological Value (BV), Protein Efficiency Ratio (PER), Net Protein Utilization (NPU), etc. This does not mean that soy is useless, but you'll generally get better results with the Milk or Egg.
Like Milk proteins, soy is available in concentrate and isolate forms.
One advantage of soy is that, depending on how it is processed, it may contain constituents known as isoflavones, which have various health benefits. Isoflavones are most often mentioned in regards to women, because they act like a weak form of estrogen. Bodybuilders cite this as a reason not to use soy, but I have yet to see a study that confirms their fears--if anything, they should be far more worried about the potential grave side effects of the illegal anabolic agents that they routinely use--ie., steroids & GH.
[This message has been edited by Armed_Man_Piker (edited 09-24-2004).]