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“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.
Since your body can’t store excess protein, it will break down any protein it doesn’t need right away and usually stow it away in fat tissue (as triglycerides), according to Merck Manuals. Rarely, if your body is in a fasting state or not getting enough calories coming in from other macronutrients, broken-down protein can be converted into glucose and used for emergency fuel, Whitney Linsenmeyer, Ph.D., R.D., nutrition and dietetics instructor in the Doisy College of Health Sciences at Saint Louis University and spokesperson for the Academy of Nutrition and Dietetics, tells SELF. But this is not typical, because the body prefers carbs as its primary source of energy (followed by dietary fat, if the body is not getting enough carbs). “We can adapt to use protein for energy as well, but it’s not ideal,” Dr. Linsenmeyer says. “Ideally, [our bodies] want to leave it alone to build and maintain body tissues.”
How much protein your body needs
Okay, so how much protein are we talking about here? The amount of protein your body actually requires for the purpose of tissue growth and repair is determined by factors like sex, age, height, weight, health, activity level, and overall calorie need, according to the U.S. National Library of Medicine. So it’s going to vary a lot from person to person.
A good starting point for roughly estimating minimum protein needs is the recommended daily allowance (RDA) for protein, or the average minimum daily intake that’s sufficient to meet the nutrient requirements (i.e. prevent a deficiency) for most healthy individuals (who are sedentary or minimally active). The RDA for protein is 0.8 grams of protein per kilogram of body weight per day, or about 0.36 grams per pound. (So you would multiply your weight in pounds by 0.36 to get your RDA.) For instance, the average 200-pound person needs at least 72 grams of protein per day to meet the RDA.