A type of protein in milk. Considered a "fast" protein because it's quickly broken down into amino acids and absorbed into your bloodstream. Not all whey proteins are the same, though -- click here to find out the best whey protein for your goals.

Another type of milk protein. Because this type is digested more slowly, it's ideal for providing your body with smaller amounts of protein for a longer period or time -- such as between meals or while you sleep.

If a soy protein is listed as the first or second ingredient, choose another product. Isoflavones, the active compounds in soy, have been shown to raise estrogen levels in men. (Build muscle and have better sex by taking control of your hormones. How? Try these 5 Ways to Boost Testosterone today!)

Contains slightly more carbohydrates and fat than purer forms, but also contains more health-promoting components. Can be clumpy. (What's the secret to a perfectly smooth protein shake? Follow these rules to blend the ultimate smoothie.)

A purer form of protein, so it contains less fat and carbohydrate.

Protein broken down into smaller fractions, so it's absorbed into your body faster than a concentrate or isolate.

Almost pure casein protein. Absorbs slowly into the bloodstream. Can be pricey.

A type of casein protein that is less expensive than micellar casein, but isn't as pure of a protein. (Sick of powder? Pick one of these Pick one of these 5 Protein-Packed Gym Snacks.)

An ingredient that mirrors milk's protein composition -- 80 percent casein, 20 percent whey.

A high-quality protein made from eggs. Good for cooking. (Yes, you can cook with protein powder! Try these 9 Super-Easy Protein Powder Recipes.)