What Is Protein & Why Do You Need It?

What Is 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 . 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 , 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 "," 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: ). "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 , 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).