Why whey?

There are plenty of sources of protein. Meat, fish and poultry are complete proteins. Nuts, beans and soybeans offer lots of amino acids too, and they become complete when you pair them with other vegetable sources of protein. Sure, it might be hard -- and messy -- to toss some silky tofu into your gym bag, but the point is that whey protein is not the only lean source of protein -- and certainly not the only way to build muscle.

Whey Protein Benefits

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­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.