The good news for vegetarians, vegans, and lovers of plant foods in general is that you can still easily get all the essential amino acids from eating a wide variety of incomplete proteins. As the FDA explains, incomplete proteins are often just lacking in one or two amino acids, so they can often make up for whatever the other one is lacking. For instance, grains are low in an amino acid called lysine, while beans and nuts are low in methionine. But when you eat, say, beans and rice or wheat toast with nut butter, you’re getting all the amino acids that you do when you eat, say, chicken. While people used to be encouraged to eat foods in combinations at meals, we now know this is not necessary, according to the U.S. National Library of Medicine, as long as you’re eating a variety of complementary incomplete proteins throughout the day.
Why we even need protein
That building block nickname is no exaggeration. The stuff is an integral component of every cell in your body, including, yes, your muscles.
“If we don’t get enough protein, our bodies actually won’t be able to rebuild properly and we’ll start to lose muscle mass,” Colleen Tewksbury, Ph.D., M.P.H., R.D., senior research investigator and bariatric program manager at Penn Medicine and president of the Pennsylvania Academy of Nutrition and Dietetics, tells SELF.
Protein helps repair the microtears that occur in your muscle fibers when they’re strained during exercise, the American College of Exercise (ACE) explains. That process of damage and repair is what maintains and grows your muscle mass.
But protein is not just important for people who work out: In addition to muscle growth and repair, protein is essential to the growth and repair of virtually all cells and body tissues—from your skin, hair, and nails to your bones, organs, and bodily fluids, according to the FDA. That’s why it’s especially important to get enough of it during developmental periods like childhood and adolescence.
Protein also plays a role in crucial bodily functions like blood clotting, immune system response, vision, fluid balance, and the production of various enzymes and hormones, per the FDA. And because it contains calories, it can provide the body energy for storage or use. (But this definitely isn’t its main gig, which we’ll get into in a bit.)
What happens in your body when you eat protein
It’s not like you eat a piece of chicken and that protein goes directly to your biceps. Dietary protein gets broken down and reassembled into the various kinds of proteins that exist in the body. No matter what kind of protein you’re eating—plant or animal, complete or incomplete—your body’s first objective is to break it back down into all the different amino acid units it was assembled from, Dr. Tewksbury explains, through the digestive process.
Then those little singular amino acids get reconfigured (by the liver) into whatever kind of protein your body needs. For instance, some proteins in the body make up antibodies that help the immune system fight bacteria and viruses. Others help with DNA synthesis, chemical reactions, or transporting other molecules, the National Institute of General Medical Sciences explains.