Proteins consist of 20 different amino acids, compounds that help control hunger and build muscle, skin and more. Eleven of the acids are nonessential, meaning our body produces them. The other nine are essential - we can't make them and must get our supply from one of two camps:
Complete proteins contain essential acids and include animal products (meat, fish, dairy, eggs), soybeans and quinoa.
Incomplete proteins fall short. "Nuts, seeds and grains are missing or low in the same essential amino acids," says Diane McKay, Ph.D., assistant professor of nutrition at Tufts University. "Legumes, fruit and veggies lack other essential amino acids." Combine on food from each incomplete group and, voila, full package. Ideally, you'd have complete proteins at every meal. But that's not always possible. A rule of thumb: If you have only incomplete proteins at one meal, choose complete ones the next time you eat.
You Complete Me
Use this food cheat sheet for easy, tasty protein matchmaking.
BREAK IT DOWN after biting into a steak or beans, protein breaks into amino acids, which are reassembled into new proteins that support:
MUSCLES amino acids build and repair muscle. The more muscle, the higher your metabolism - and the more calories you burn.
APPETITE your body torches double the calories digesting protein versus carbohydrates or fat. Amino acids trigger fullness hormones.
BLOOD hemoglobin, a protein in red blood cells, carries oxygen throughout your body.
BONES nearly 30 percent of bone weight is collagen, another protein.
HAIR AND NAILS both are made of keratin, a protein that's constantly replenished (aka growing) as new amino acids arrive.
IMMUNITY amino acids help form illness-fighting antibodies.