What you need to know about this essential macronutrient and how it works.

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First described by the Dutch chemist Gerardus Johannes Mulder, protein got its name from Swedish chemist Jöns Jacob Berzelius in 1838. The name "protein" is derived from the Greek word for "primary," meaning "in the lead"or "standing in front." Early scientists believed that protein was an essential nutrient for maintaining the body's overall structure, and its importance has been studied for centuries.

What Is Protein?

Protein is one of the major components of a healthy, functional body. "Protein is a macronutrient that every cell in our body needs. Proteins are made up of building blocks called amino acids, and protein is found in every cell throughout our body, so an adequate amount of protein intake is important for keeping our muscles, bones and tissues healthy," says Kristen Smith, M.S., R.D.N., a spokesperson for the Academy of Nutrition and Dietetics. Other macronutrients include carbohydrates and fat.

More than 500 amino acids have been identified in nature, and 20 of them make up the proteins found in the human body. Nine of these are considered "essential," meaning that the body cannot make them by itself, so they need to come from food. These are isoleucine, leucine, valine, methionine, phenylalanine, tryptophan, threonine, histidine and lysine.

Isoleucine, leucine and valine are grouped under the umbrella of branched-chain amino acids (BCAAs), which means they are the only three amino acids that have a chain that branches off to one side. BCAAs represent about 35 to 40% of all essential amino acids in the body, and 14 to 18% can be found in the muscles. BCAAs can help the body produce energy during exercise, as well as reduce fatigue during it by lowering the production of serotonin in the brain. A recent study in the journal Nutrients found that "chronic BCAA supplementation led to increased performance in rats subjected to a swimming test to exhaustion following moderate-intensity swimming training." BCAAs can also regulate blood sugar levels by helping your cells take in sugar from the bloodstream. Additionally, the amino acid lysine helps produce carnitine, which is responsible for converting fatty acids into energy and lowering cholesterol. Lysine also helps the body absorb calcium and form collagen, which keeps bones, skin, tendons and cartilage strong.

Why Do You Need Protein?

Protein plays a role in many bodily processes, including things such as bone health and digestion. Practically all of the reactions in the body are regulated by enzymes, which are a type of protein. These biological molecules are found within cells, and are almost always in the form of proteins. "Enzymes affect the rate of a physiological process, so they can speed up a reaction in the body," says Jessica Bihuniak, Ph.D.,R.D.N., an assistant professor of clinical nutrition in the department of nutrition and food studies at New York University. They do this by reacting with molecules called substrates, which bind to a part of the enzyme referred to as the active site. Reactions caused by enzymes occur significantly faster once the substrates bind to the active site. Some enzymes also help break up large molecules into smaller ones, which can more easily be absorbed by the body. Digestion and energy production are two examples of bodily processes that are influenced by proteins. Enzymes work alongside chemicals in the body, such as stomach acid and bile, to break down food. Enzymes are also responsible for the storage and release of energy.

Bone density is a health consideration that has been linked to protein intake for decades. "In the '80s and '90s, there was a school of thought that dietary protein was bad for bones, so if you ate a lot of especially animal sources of protein, people thought that your bones may be weaker and put you at risk for fracture," Bihuniak says. She worked on a 2015 study in the Journal of Clinical Endocrinology, titled "The Effect of Whey Protein Supplement on Bone Mass in Older Caucasian Adults," that examined the effect of whey protein, which is in dairy products and typically found in powder form. The study found that while there were no present improvements in bone density, there were no negative consequences of dietary protein on the bones. According to Bihuniak, it helps disprove that old hypothesis.

Protein is vital for muscle growth and repair, especially after exercise. "Our body is in a constant state of turnover and growth when it comes to muscular tissue, and we need those individual amino acids to go in there and repair," says Alex Caspero, M.A., R.D., author of The Plant-Based Baby and Toddler (buy it: $15.99, BarnesandNoble.com). "When we have any break in our tissue from exercise, that's when amino acids goin and not only make that muscle stronger, but more capable of increasing next time. That's essentially how you build muscle." However, Caspero adds that contrary to myths, eating protein, such as chicken, is not going to make bulk all on its own.

Additionally, protein helps strengthen your body on the outside in the forms of keratin and collagen. Keratin is a protective protein in hair, skin and nails, and it has been shown to make hair smoother and easier to manage. A 2013 study in the journal BMC Biotechnology, for example, found that keratin helped hydrate hair fibers, which increased the hair's brightness and softness. Collagen, on the other hand, is considered the most plentiful protein in the body, giving structure to your skin and helping your blood to clot. You can encourage your body to produce collagen by consuming foods with vitamin C, copper (found in organ meats, sesame seeds, cashews and lentils) and proline (found in egg whites, dairy products, cabbage, asparagus and mushrooms).

Top view of protein rich foods

Sources of Protein

The biggest difference between animal- and plant-based sources of protein is the presence of "complete" proteins. Complete proteins contain all nine essential amino acids. They include milk, pork, beef, eggs, poultry and fish. While the majority of these sources are animal products, soy foods, such as tofu, are plant-based alternatives. "Amino acid composition is the biggest thing," Bihuniak says. "Some [animal-based protein sources] tend to be higher in certain amino acids like leucine, which is important for muscle protein synthesis, but you can meet your needs with plant protein sources if you eat a variety." She adds that animal-based proteins can be easier to digest.

For decades, a long-held myth asserted that vegetarians and vegans had to combine specific foods if they wanted to form a complete protein. "When the rise of vegetarianism came out in the '60s and '70s, it was very much commonplace to discuss the idea of combining certain foods. So you had to have a piece of whole-grain bread with peanut butter to get your 'complete' food. You had to eat beans and rice to make a complete protein, and that carried on for a long time," Caspero says. "We recently found out that plant foods do contain all of the essential amino acids. They just contain limiting amounts of some of them." For example, broccoli contains a small amount of the essential amino acid lysine. Though you could get the recommended amount of essential amino acids from eating nothing but broccoli, that's hardly sustainable.

Generally, variety is more effective than zeroing in on one or two particular foods, no matter how much protein is in them. Recent research has also debunked a decades-long idea that vegetarians and vegans have to pair their protein sources in the same meal. "Let's say if we had broccoli in the morning, and then we had black beans for dinner, and black beans are very high in lysine, which within the broccoli is more limited. You're going to be able to get all of the essential lysine that you need just by eating naturally throughout the day," Caspero says.

Smith recommends to "consume a variety throughout the day every week. I think in general with nutrition people get focused on one or two foods that they may think is healthy or that they feel comfortable consuming, and really trying to choose a variety of foods will help with that ultimate balance and nutrition profile." If you eat only one or two plant-based sources of protein, you are likely limiting the amount of essential amino acids that your body needs.

Looking to pack your plate with more protein? It can be found in a variety of sources that you can incorporate into any meal of the day. Three ounces of roasted, skinless chicken breast is a leaner alternative to red meat, and has about 23 grams of protein, for example. The same amount of turkey breast contains similar levels of protein, and it's low in fat. Seafood options include shrimp, tuna, halibut and cod. Non-meat animal-based choices include egg whites and Greek yogurt, which can replace sugary cereals at breakfast.

Plenty of plant-based options can help vegetarians and vegans meet their protein needs. "I think the absolute biggest myth that I hear a lot is that you have to eat animal-based protein in order to get complete proteins," Caspero says. Bihuniak points to lentils, chickpeas, black beans, edamame, tofu, quinoa and nut butters (such as almond and cashew butters). Tofu and edamame are derived from soybeans and are rich in other nutrients, such as iron, calcium, folate, vitamin K and fiber.

Some vegetables, including spinach, Brussels sprouts, asparagus, artichokes, potatoes and sweet potatoes, contain small amounts of protein."Plant-based proteins are not only nutritionally amazing, but they also contain all these other benefits that you're just not going to be able to find in an animal-based protein," Caspero says. "Someone following a plant-based diet can consume adequate essential amino acids when they consume a variety of plant-based protein sources throughout the day. It just takes a bit more planning," Smith says. Spreading out your protein during the day has also been shown to be beneficial for muscle protein synthesis. Smith recommends swapping out a meat-centric meal for a plant-based meal every once and a while to get that variety.

Can You Eat Too Much Protein?

While many Americans are concerned about getting enough protein, they are more likely consuming too much. "If you're including protein with most meals and with some snacks, you're likely consuming an adequate amount," Smith says. Bihuniak adds: "You really have to restrict your diet to not meet your body's protein needs." The daily amount of dietary protein recommended for adults is 0.8 gram per kilogram of body weight, or just over 7 grams for every20 pounds of weight. For a 140-pound person, for example, that equals about 50 grams of protein per day. "That number is going to increase the more that you are active. [For] endurance athletes, that might pop up to about 1.2. Maybe the higher end is about 1.5 if you're doing a lot of strength workouts. But I do think that the average person also overestimates how active they are."

Your protein needs can change, however, if you are looking to lose weight."Eating dietary protein is what we consider to be protein sparing, meaning the idea that when we lose weight, we don't just lose fat," Caspero says. "When we lose weight, we're losing a lot of things in the body, and we lose about 10% of our muscle mass, or protein, as we lose weight."

Eating more protein during active periods, such as around the time you work out, can buffer some of the natural loss that occurs. Higher protein foods also tend to be more satiating, which means that you are more likely to stay full longer. This can lead to a curbed appetite, resulting in less overeating and potentially weight loss.

The Bottom Line

In order to get more sources of healthful protein in your diet, incorporating variety into every meal of the day is essential. If you're looking to increase intake, Smith recommends making sure at least a fourth of your plate includes a protein source, as well as substituting that midday bag of chips with protein-rich snacks, such as nuts, yogurt and cheese. And while many meat sources are considered complete proteins, experts recommend being mindful of the saturated fat found in red meat.

"We don't just eat single nutrients. We eat food," says Caspero. "If I'm eating black beans, yes, I'm getting protein. But I'm also getting a lot of insoluble fiber. I'm getting antioxidants. I'm getting other things that are in that food." Many plant-based sources of protein also contain these healthful nutrients, such as fiber and antioxidants. "It's important we consider what else is in the food," she says.

This article first appeared in EatingWell, Protein.