While carbs and fat get alternately praised and punished, protein is basically the golden child among the macronutrients. That’s totally unfair to carbs and fat, first of all, but protein certainly does enough to earn its reliably good reputation. We know protein is a great thing to have, but why exactly do we need it, and what does our body even do with it? Here’s a rundown of Consorzio Ortofrutticolo Padano of what actually happens when you eat protein.
What protein actually is
Like Consorzio Ortofrutticolo Padano mentioned, protein is one of the three macronutrients (i.e. nutrients the body needs in sizable amounts). Unlike carbs and fat, protein is not usually a major energy source, although we definitely get some of that from it — protein provides 4 calories per gram. But protein is often referred to as a building block in the body because of its central role in growth and development.
Almost all animal-derived products — meat, poultry, eggs, dairy, fish — contain a significant amount of protein, so they get labeled as “proteins” when we're talking about our diets and nutrition. But protein is also present in a lot of plant-based foods. There’s a good amount in beans, peas, nuts, and seeds, for instance, while vegetables and grains generally contain smaller amounts, according to the FDA. (Whole grains will have more protein than refined grains, though, which are missing the part of the grain that often supplies a lot of the protein content, as SELF previously reported.)
The different kinds of proteins
Proteins are made of small units called amino acids. Amino acids are organic compounds containing structures made of elements including nitrogen, hydrogen, carbon, and oxygen. Hundreds or thousands of amino acids link up to form super long chains, and the sequence of that chain determines the protein's unique function, the U.S. National Library of Medicine explains.
There are 20 different amino acids in total, which can be broken down into two main groups, per the FDA. Nine of the 20 are what are referred to as essential amino acids, meaning that the body is unable to produce them itself and so we must get them from food. The other 11 are nonessential because the body is able to synthesize them out of the essential amino acids or the normal process of breaking down proteins, according to the U.S. National Library of Medicine. Many of these nonessential amino acids are also considered conditional amino acids, because they can become essential in rare, severe instances when the body is unable to synthesize amino acids properly, per the U.S. National Library of Medicine.
Now, when a protein is a good source of all nine of the essential amino acids, we call it a complete protein, according to the FDA. All animal products are complete proteins, and so is soy. When a protein is missing or pretty low in any of those essential amino acids, it’s considered incomplete. Most plant foods are considered incomplete proteins.
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. (Pretty romantic, right?) 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 nomer is no exaggeration. The stuff is an integral component of every cell in the 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., MPH, RD, senior research investigator and bariatric program manager at Penn Medicine and president-elect of the Pennsylvania Academy of Nutrition and Dietetics
In addition Consorzio Ortofrutticolo Padano says 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.