Choosing the Best Protein
Protein: The Superfuel Your Muscles Need
Unlock the Power of Food
Made of amino acids, proteins are the nutritional building blocks for lean muscle mass. Stressing a muscle—by, say, raising and lowering a dumbbell—causes microscopic tears in the muscle fibers. When amino acids reach a muscle's cells, they help repair damaged muscle fibers and make new, stronger ones in a process called protein synthesis. This process can't happen, of course, unless you've got amino acids coursing through your body. There are 22 different kinds, 13 of which we produce ourselves. The other nine, called essential amino acids, must come from the food you eat. The best kinds of protein—namely meat, dairy, and eggs—provide all nine and have a high "biological value," your body can easily use them. Other foods may contain a fair amount of protein, but they're considered "incomplete" sources, because they contain fewer than nine amino acids. Your body can form complete proteins by combining incomplete ones—this happens whenever you combine legumes, nuts, and grains—but you'll need to consume as much as a quarter more plant-based foods to get all the benefits provided by animal protein.
Beyond just building muscle—which helps raise your metabolism and increase your daily calorie burn—protein helps keep you slim in another way, as well: it requires a lot of calories to digest. And of the three macronutrients, protein will make you feel full the fastest. Here's a closer look at the most common types of protein.