What Are the Functions of Protein in the Human Body?

Protein is found throughout your body — in muscle, bone, ligaments, skin, hair, blood and virtually every tissue. In fact, every living cell and all bodily fluids except bile and urine contain protein. Different types of proteins, functioning as enzymes, hormones and their component amino acids, are essential for every metabolic function in your body.

Foods high in protein provide energy and are necessary for your overall health. (Image: Aamulya/iStock/GettyImages)


As a highly evolved, diverse class of molecules, proteins perform endless tasks in your body, such as providing support for your body, regulating hormones for immune health, converting chemical energy into mechanical energy and playing a role in your growth and development.

How Much Do You Need?

You need to include protein in your diet every day because your body doesn't store protein the way it stores fats or carbohydrates. How much you need depends on your age, sex, health and level of physical activity.

The average person requires a specific daily amount of protein, according to USDA ChooseMyPlate:

  • Boys 14 to 18 years of age need 6 1/2 ounces; girls in the same age group need 5 ounces.
  • Women 19 to 30 years of age need 5 1/2 ounces; men in the same age group need 6 1/2 ounces.
  • Women 31 to 50 years of age need 5 ounces; men in the same age group need 6 ounces.
  • Women 51 years and older need 5 ounces; men in the same age group need 5 1/2 ounces.

In general, 1 ounce is equal to either 1/4 cup of cooked beans, 1 egg, 1 tablespoon of peanut butter or 1/2 ounce of nuts or seeds. Use the nutrition labels on food or an online database like MyPlate to determine the specific amount of protein in each food.

Sources and Types of Protein

Protein is composed of more than 20 amino acids, which are the basic building blocks of your body. According to MedlinePlus, amino acids may be divided into three different types of protein:

  • Essential amino acids — not made by the body but supplied by food
  • Nonessential amino acids — made by the body from essential amino acids or in the normal breakdown of proteins
  • Conditional amino acids — needed in times of illness and stress

Proteins from animal products, such as meat, fish and dairy, are known as complete proteins because they supply all nine of the amino acids the body can't make on its own. Most vegetable protein is considered incomplete because it lacks one or more of the essential amino acids. But if you combine different types of plant proteins every day, you can get all of the amino acids your body needs. Soy, beans, legumes, hempseed, nut butters and quinoa are good examples of plant protein sources, according to Piedmont Healthcare.

Providing Support and Aiding Movement

An important function of protein is to provide support in your body, which involves connective tissues, cartilage and bone. Contractual protein is responsible for muscle contraction and movement. Structural protein assures that your cells maintain their shape and resist deformity. Keratin is a structural protein found in your hair, nails and skin. Collagen is another structural protein that provides the framework for the ligaments that hold your bones together, in addition to the tendons that attach muscles to those bones.

Serving the Immune System

Antibodies are specialized proteins that travel through the bloodstream defending the body from antigens, such as bacteria, viruses, infections and disease. By binding to antigens, antibodies neutralize and immobilize foreign molecules so they can be destroyed by white blood cells. There are five different types of antibodies. Each type is found in different parts of the body, and each has a specific duty in maintaining the health of your body.

Regulating Body Processes

Body processes are influenced by hormones — proteins that act as chemical messengers to help cells, tissues and organs communicate, according to Colorado State University. For example, they signal the uptake of glucose into a cell, stimulate the growth of tissue and bone, signal the kidneys to reabsorb water and aid in almost all facets of metabolism in your body.

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