Why Your Body Needs Proteins: Essential Benefits and Functions Explained

The body needs protein to build and repair tissues, make enzymes and hormones, and support immunity.

Roles

• Build and repair tissue: muscle, skin, hair.
• Enzymes and hormones.
• Immune system: antibodies.
• Transport: hemoglobin.
• Fluid balance.
• Energy: 4 calories per gram.

Amino acids

Twenty amino acids make protein. Nine are essential.

Daily

RDA 0.8 g per kg.

Sources

Meat, fish, eggs, dairy, beans and nuts.

Deficiency

Causes swelling (kwashiorkor).

Functions

Proteins are chains of amino acids that build and repair tissues, make enzymes and hormones, carry molecules like hemoglobin and form antibodies. There are 20 amino acids, 9 of which are essential and must come from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

• The RDA is 0.8 g of protein per kg of body weight per day for adults, or about 56 g for a 70 kg man and 46 g for a 57 kg woman.
• Athletes and older adults may need 1.2 to 2.0 g per kg, according to sports nutrition guidance.
• Muscle makes up about 40 percent of body weight, and protein turnover is constant.

Sources and shortage

Complete proteins come from meat, fish, eggs, dairy and soy. Beans, grains and nuts can be combined over the day. Deficiency (kwashiorkor) causes edema, muscle wasting and weakened immunity, and affects malnourished children globally. Excess protein in people with kidney disease can be harmful, so check with a doctor.

Functions

Proteins build and repair tissue, make enzymes and hormones, support immunity and transport molecules. Hemoglobin is a protein that carries oxygen. Muscle is about 20 percent protein. The body breaks proteins into amino acids and uses them for synthesis.

Sources and shortage

Adults need 0.8 g per kilogram daily. Sources are meat, fish, eggs, dairy, legumes and soy. Deficiency causes muscle loss, edema and weak immunity.

Biochemical roles

The body contains about 100,000 different proteins. Enzymes such as amylase speed up reactions; antibodies defend against infection; collagen provides structure and makes up about 30 percent of body protein; insulin is a protein hormone. Proteins also buffer pH and carry molecules. Protein supplies 4 calories per gram.

Intake and shortage

Older adults may benefit from 1.0 to 1.2 g per kg to limit sarcopenia, per the PROT-AGE group. Protein deficiency is uncommon in the US, but affects millions in food insecure regions. Kwashiorkor shows as edema and a swollen belly in children. Excess protein is not stored but converted, and in kidney disease high intake strains the kidneys.

Based on data from the National Academies of Sciences and the World Health Organization