For people experiencing significant growth -- children, adolescents, pregnant women -- protein is important. These bodies aren't just maintaining, they're producing.
Similarly, athletes use a lot of protein as well -- the process of building muscle is one of constantly tearing and repairing skeletal muscle cells. In fact, you can't build muscle without what's called a "positive protein balance." That means your protein synthesis -- your production of protein -- must be greater than the destruction of muscle the exercise causes. To boost protein synthesis, some physicians recommend consuming protein after a workout.
For athletes -- and the people who want to look like them -- the form of that protein can be important. A two-tablespoon serving of peanut butter could be a great post-workout snack -- but it comes loaded with about 18 grams of fat [source: Peanut Institute]. If you're trying to lose weight, maintain your heart health or achieve lean bodybuilder-style definition, the fat, cholesterol and calories associated with many forms of protein could be a problem.
That's why some people turn to supplements. Whey protein isolate is fat-free, and it's filling. It also has a very high biological value, or BV. BV is a measure of the body's ability to absorb a protein. The naturally occurring protein source with the highest BV is an egg, with a BV of 100. Whey protein is around 104 -- its score can vary depending on its form [source: Whey Protein]. Basically, whey protein is pure, no-frills protein, designed to be absorbed thoroughly and quickly. The speed of absorption matters because it affects the anabolic, or muscle-building, qualities of the protein.
A high-protein, no-fat supplement sounds like it packs a pretty strong one-two punch. Before you get too excited, though, better learn about the side effects.