Whey protein is the name for a collection of globular proteins that can be isolated from whey, a by-product of cheese manufactured from cow's milk. It is typically a mixture of beta-lactoglobulin (~65%), alpha-lactalbumin (~25%), and serum albumin (~8%), which are soluble in their native forms, independent of pH. Whey has the highest Biological Value (BV) of any known protein.
Whey protein typically comes in three major forms: concentrate, isolate and hydrolysate. Whey protein concentrates contain a low level of fat and cholesterol but generally have higher levels of bioactive compounds, and carbohydrates in the form of lactose — they are 29%-89% protein by weight. Isolates are processed to remove the fat, and lactose, but are usually lower in bioactive compounds as well — they are 90%+ protein by weight. Hydrolysates are predigested, partially hydrolyzed whey proteins which consequently are more easily absorbed, but their cost is generally higher.
Whey protein powder is commonly used by bodybuilders and other athletes to accelerate muscle development and aid in recovery.