Protein is a macronutrient that is essential to building muscle mass. It is commonly found in animal products, though is also present in other sources, such as nuts and legumes.
There are three macronutrients: protein, fats and carbohydrates. Macronutrients provide calories, or energy. The body requires large amounts of macronutrients to sustain life, hence the term “macro,” according to the University of Illinois McKinley Health Center. Each gram of protein contains 4 calories. Protein makes up about 15 percent of a person’s body weight.
Chemically, protein is composed of amino acids, which are organic compounds made of carbon, hydrogen, nitrogen, oxygen or sulfur. Amino acids are the building blocks of proteins, and proteins are the building blocks of muscle mass, according to the National Institutes of Health (NIH).
“When protein is broken down in the body it helps to fuel muscle mass, which helps metabolism," said Jessica Crandall, a registered dietitian nutritionist, certified diabetes educator and national spokesperson for the Academy of Nutrition and Dietetics. "It also helps the immune system stay strong. It helps you stay full. A lot of research has shown that protein has satiety effects.”