No matter how hard you try, without protein you simply can't put on mass or retain your shape while dieting. But how much do you really know about this essential nutrient? It isn't as simple as eating 0.8 gram per pound of bodyweight (or 1 gram . . . or 2 grams). A multitude of factors affect how digestible and usable a protein is, as well as how the body will use it, whether for building or for stoking its furnace. Protein quality, meal timing and other nutritional factors all play a role in how protein will be used. For a bodybuilder interested in building muscle, choosing the right proteins is job one—so read on!

Amino Acids: Form & Function Form Function Pros Cons FREE-FORM Doesn't require digestion Allows intake of single amino acids in high doses (some single amino acids reduce muscle catabolism or have other specific benefits) Relatively expensive HYDROLYZED PROTEIN Predigestion speeds absorption Shorter chain length peptides (if available) may increase anabolic hormone (IGF-1) levels BRANCHED-CHAIN Increases ammonia production during exercise, which acids in formation of alanine from glucose Can be converted into energy to prevent muscle catabolism Relatively expensive form of energy for muscle action DI-/TRIPETIDES Two and three-amino acid molecules that are quickly absorbed Increase anabolic hormone (IGF-1) levels in burn patients (increases protein utilization) Cost, availability PLANT PROTEINS Proteins appropriate for vegans, vegetarians and omnivores (chiefly from legumes, nuts, grains) Inexpensive and often fat-free; rich in antioxidants, fiber, etc. Often incomplete (exception: soy); must combine complementary proteins ANIMAL FOODS Dairy, poultry, eggs, beef, etc., rich in essential amino acids Usually complete (contain all essential amino acids: exception: gelatin) Often high in saturated fat