Protein is an essential part of the diet because it provides amino acids the body needs to function correctly. People need daily protein sources from their food, which they can get from animal or plant proteins.

This article looks at how much protein someone needs each day and why this amount may vary. It also describes amino acids, their role in the body, and the effects of protein deficiency. Finally, it includes sources of protein and tips to get enough protein in the diet.

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Protein is a macronutrient, and each gram provides four calories.

Amino acids are the building blocks of proteins in food. In nutrition, amino acids are either essential or non-essential. People need to consume essential amino acids in foods.

The nine essential amino acids are:

  • Phenylalanine
  • Valine
  • Tryptophan
  • Threonine
  • Isoleucine
  • Methionine
  • Histidine
  • Leucine
  • Lysine

Scientists consider amino acids such as arginine and histidine to be conditionally essential, as the body may not make enough of them during times of growth or trauma.

When a single protein source contains all nine essential amino acids, nutritionists refer to it as a “complete protein.” Animal-based proteins such as meat are complete sources of protein. People who eat a plant-based diet can obtain all of the essential amino acids by eating a combination of foods.

Learn more about protein here.

According to the Dietary Guidelines for Americans 2020-2025, people need different amounts of daily protein depending on their age and sex. Those amounts include:

  • 56 grams (g) for adult males
  • 46 g for adult females
  • 34 g for children aged 9-13 years
  • 13 g for children aged 2-3 years

A person who is pregnant or breastfeeding requires 71 g of protein per day.

Experts base guidelines on healthy adults who do minimal activity. People who do more activity or who build muscle through exercise may require more protein in their diet, although recommended amounts vary.

For a person doing moderate to intense physical activity, the recommended intake is between 1.3 g – 1.6 g per kilogram (kg) of body weight per day

However, the International Society of Sports Nutrition recommends higher levels of 1.4 g to 2.0 g per kg of body weight per day.

People can also calculate the amount of protein they need by using the guidelines of 0.8 g protein per kg of body weight per day. However, according to 2016 study, consuming up to 2 g of protein per kg of body weight per day is safe for healthy adults

Another study indicates that older people who are moderately or severely ill may require between 1.2 to 1.5 g of protein per day per kg of body weight.

Protein is an essential part of the diet, and the body needs it for numerous processes.

The United States Food and Drug Administration (FDA) advise that protein plays roles in the following aspects of human health:

  • ensuring correct growth and development, especially during childhood, adolescence, and pregnancy
  • building and repairing cells and body tissues
  • maintaining and building healthy skin, hair, nails, muscle, bone, and internal organs
  • producing hormones, neurotransmitters, antibodies, and enzymes
  • helping blood to clot, balancing fluids, and supporting the immune system

The body incorporates dietary amino acids into skeletal muscle and other tissues as needed. During fasting or stress, the muscles can release the amino acids for the body to utilize.

Learn more about essential amino acids here.

The Dietary Guidelines for Americans 2020-2025 recommend that people vary the sources of protein they eat, and limit or avoid saturated fat sources such as processed and red meat.

Sources of protein include:

  • meat and poultry such as beef, lamb, pork, chicken, turkey, game, liver, and sweetbreads
  • chicken and other birds’ eggs
  • dairy products, including milk, yogurt, cheese, and cream
  • seafood such as white fish, oily fish, scallops, shrimp, crab, and oysters
  • nuts and seeds, including Brazil nuts, cashews, hazelnuts, almonds, walnuts, hemp seeds, pumpkin seeds, chia seeds, and sunflower seeds
  • beans and pulses such as lentils, chickpeas, black beans, navy beans, butter beans, and cannellini beans
  • soy products, including tofu, natto, tempeh, soy milk, and soy yogurt
  • plant-based proteins such as seitan and mycoprotein

According to a 2016 review, many children in developing countries are missing essential amino acids, leading to growth and development issues. However, the United Nations’ (UN) emphasis on protein malnutrition has waned since the 1970s, say the reviewers.

Another review estimates that one billion people worldwide have inadequate protein intake.

The Dietary Guidelines for Americans 2020-2025 suggests that about three-quarters of Americans meet or exceed the recommendation for consumption of meats, poultry, and eggs. However, almost 90 percent do not meet the guidelines for seafood, and more than half do not meet the recommendation for nuts, seeds, and soy products.

A lack of essential amino acids can not only occur in developing countries but also in older adults with inadequate care.

Clinical symptoms of protein deficiency can include:

  • depression
  • anxiety
  • insomnia
  • fatigue
  • weakness
  • stunted growth in children

According to a review, kwashiorkor and marasmus are examples of more severe clinical disorders caused by malnutrition and inadequate intake of essential amino acids.

Learn more about malnutrition here.

People can get enough protein by including suitable food sources in each meal and snack.

Animal-based sources

Here are some meal ideas for how a person can incorporate more poultry, eggs, dairy, fish, and lean meats into their diet:

  • chicken breast, sweet potato, and greens
  • scrambled egg with tomato and spinach
  • pancakes with Greek yogurt and fruit
  • salmon, purple sprouting broccoli, and sweet potato mash

Vegan sources

A person following a vegetarian or vegan diet needs to ensure they get all the essential amino acids by including various types of protein. Here are some suggestions for the kinds of meals that can help a person incorporate sufficient protein:

  • Bolognese made with lentils and zucchini noodles
  • vegetable soup served with oatcakes
  • protein powder smoothie with fruit and oat milk
  • crispy tofu bowl
  • vegetable and hummus wrap

Learn more about healthy foods here.

People can ensure they get enough protein by including varied sources in their diet every day. Meat, fish, and dairy products are complete sources of protein. Eating a variety of different plant sources ensures that people eating a plant-based diet get essential amino acids.

People can add beans, nuts, and seeds to their meals as additional protein sources, or try adding protein powder to smoothies. Consuming up to 2 g of protein per kilogram of body weight a day is safe for healthy adults.