Protein is an important part of every diet. The amount of protein an individual needs depends on their age and sex.

Protein is a part of every cell in the body. It helps the body to build and repair cells and tissues. Protein is a major component of the skin, muscle, bone, organs, hair, and nails.

According to the Food and Drug Administration (FDA), most people in the United States get enough protein from their diets to meet their needs.

This article looks at protein, its function, sources, and how much protein different groups of people need each day.

A pretty blue plate full of high-protein foods, mostly beans and maybe chicken. A person is sticking a fork into the beans.Share on Pinterest
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Protein is one of three macronutrients, which are nutrients the body needs in larger amounts. The other macronutrients are fat and carbohydrates.

Protein is made up of long chains of amino acids. There are 20 amino acids. The specific order of amino acids determines the structure and function of each protein.

The 20 amino acids that the body uses to create protein are:

  • alanine
  • arginine
  • asparagine
  • aspartic acid
  • cysteine
  • glutamic acid
  • glutamine
  • glycine
  • histidine
  • isoleucine
  • leucine
  • lysine
  • methionine
  • phenylalanine
  • proline
  • serine
  • threonine
  • tryptophan
  • tyrosine
  • valine

There are nine essential amino acids that the human body does not synthesize, so they must come from the diet.

Proteins may be either complete or incomplete. Complete proteins are proteins that contain all essential amino acids. Animal products, soy, and quinoa are complete proteins.

Incomplete proteins are proteins that do not contain all essential amino acids. Most plant foods are incomplete proteins, including beans, nuts, and grains.

People can combine incomplete protein sources to create a meal that provides all essential amino acids. Examples include rice and beans, or peanut butter on whole wheat bread.

What does protein do in the body?

Protein is present in every body cell, and an adequate protein intake is important for keeping the muscles, bones, and tissues healthy.

Protein plays a role in many bodily processes, including:

  • blood clotting
  • fluid balance
  • immune system responses
  • vision
  • hormones
  • enzymes

Protein is important for growth and development, especially during
childhood, adolescence, and pregnancy.

According to the Dietary Guidelines for Americans 2015–2020, a healthful eating pattern includes a variety of foods containing protein. Both animal and plant foods can be excellent sources of protein.

The guidelines classify the following foods as protein foods:

  • seafood
  • lean meats and poultry
  • eggs
  • legumes, which include beans and peas
  • nuts
  • seeds
  • soy products

Dairy products, such as milk, cheese, and yogurt, also contain protein. Whole grains and vegetables contain some protein, but generally less than other sources.

Animal products tend to contain higher amounts of protein than plant foods, so people following a vegetarian diet or a vegan diet may need to plan their meals to ensure they meet their protein needs.

Read about plant-based sources of protein here.

The FDA advise that people can tell if a food product is high or low in protein by checking the label.

Foods that provide 5% or less of a person’s daily value (DV) are considered low in protein.

Foods with 20% DV or more are considered high in protein.

A person does not need to consume foods containing all the essential amino acids at each meal because their body can use amino acids from recent meals to form complete proteins. Eating a variety of protein foods throughout the day is the best way for a person to meet their daily protein needs.

Read about some healthful high protein foods here.

The FDA recommend that adults consume 50 grams (g) of protein a day, as part of a 2,000-calorie diet. A person’s daily value may be higher or lower depending on their calorie intake.

The Dietary Guidelines for Americans 2015–2020 provide the following recommended daily amounts (RDA) for protein by sex and age group:

AgeProtein RDA
child aged 1–313 g
child aged 4–819 g
child aged 9–1334 g
female teen aged 14–1846 g
male teen aged 14–1852 g
female adult aged 19+46 g
male adult aged 19+56 g

Many factors can affect how much protein a person needs, including their activity level, weight, height, and whether they are pregnant.

Other variables include the proportion of amino acids available in specific protein foods and the digestibility of individual amino acids.

The USDA provide a calculator to help people work out how much protein and other nutrients they need.

Protein and calories

Protein is a source of calories. Generally, protein and carbohydrates contain 4 calories per gram. Fats contain 9 calories per gram.

The Dietary Guidelines for Americans recommend that between 10–35% of an adult’s daily calories should come from protein. For children, it is 10–30%.

Most people in the U.S. meet their daily protein needs. On average, men get 16.3% of their calories from protein, and women 15.8%.

Some diets recommend eating more protein in order to lose weight.

Aa 2015 review suggests that following a particular type of high-protein diet may encourage weight loss, but researchers need to do further studies to establish how to implement such a diet effectively.

When increasing protein intake, it is important to make sure that the diet still contains adequate amounts of fiber, such as fruit, vegetables, and whole grains.

Replacing processed foods and sources of unhealthful fats or sugar in the diet with protein can promote a healthful diet.

Before making significant changes to their diet, it is a good idea for a person to talk to their doctor about the best strategies and tips.

Read about high protein diets here.

Protein deficiency due to a low intake of protein in the diet is unusual in the U.S.

However, a lack of protein in other countries is a serious concern, especially in children. Protein deficiency can lead to malnutrition, such as kwashiorkor and marasmus, which can be life threatening.

Protein deficiency can arise if a person has a health condition, including:

Very low protein intake can lead to:

  • weak muscle tone
  • edema or swelling due to fluid retention
  • thin, brittle hair
  • skin lesions
  • in adults, a loss of muscle mass
  • in children, growth deficits
  • hormone imbalances

Protein shakes and protein powders contain high amounts of protein. Protein powders may contain 10–30 g of protein per scoop. They may also contain added sugars, flavorings, vitamins, and minerals.

Protein in protein shakes or powders can come from:

  • plants, such as peas or soybeans
  • milk, such as casein or whey protein
  • eggs

Building and repairing muscle requires protein. Many athletes and bodybuilders use protein products to boost muscle growth.

A wide range of protein supplements is currently available, many claiming to encourage weight loss and increase muscle mass and strength.

A 2018 review reported that taking protein supplements significantly improved muscle size and strength in healthy adults who do resistance exercise, such as weight lifting.

However, protein shakes and powders count as dietary supplements, and so they are not regulated by the Food and Drug Administration (FDA). This means people cannot guarantee that the products contain what the manufacturer claims they do.

Some supplements may also contain banned or unhealthy substances, such as heavy metals or pesticides.

Many protein products are high in added sugar and calories, which can lead to spikes in blood sugar and weight gain, so it is important to check the labels.

Most people, including athletes, can get enough protein from a balanced diet without supplements. Getting too much protein consistently can cause serious health problems.

Some people may benefit from using protein powder to address health concerns, including those with:

  • a reduced appetite, which may result from older age or cancer treatment
  • a wound that is not healing well, as protein can help the body repair and replace cells
  • a medical condition, such as a serious burn, that requires additional calories and protein

For most people, a varied and healthful diet will provide enough protein. For the best health benefits, people can get their protein from a variety of sources. These include fish, meat, soy, beans, tofu, nuts, and seeds.

Here are some suggestions for adding more protein to diet:

  • Replace regular snacks with high protein snacks, such as nuts, roasted chickpeas, and peanut butter.
  • Add beans and peas to soups, side dishes, or salads. These also make great main dishes.
  • Include one high protein food with each meal.
  • Replace a source of carbohydrate with a source of protein, such as swapping out a piece of toast for an egg in the morning.
  • Before adding protein bars to the diet, check the labels, as they can be high in sugar.

To limit fat intake while increasing protein intake, choose lean meat, poultry, and dairy products, or trim the fat before eating. Try using cooking methods that do not add extra fat, such as grilling.

Avoid processed meats and other processed foods, as these can have negative health effects. Choose nutrient-rich foods instead of processed foods when possible.

Protein is an important part of every diet. The FDA recommend that adults consume 50 grams (g) of protein per day as part of a 2,000-calorie diet, though a person’s specific needs depend on their age, sex, activity levels, and other factors.

Most people in the U.S. meet their daily protein needs. If a person wants to increase their protein intake, they can do so by including healthful, high protein foods with each meal.