All About Protein: Nutrition, Food Sources, and More

Medically Reviewed
illustration of different types of protein
You can get protein from a variety of plant and animal sources.Shutterstock

Protein needs no introduction. You likely already know it as one of the three major macronutrients that make up your diet (the other two being fat and carbohydrates). (1)

There are hundreds of products — from supplements to energy bars — designed to make it easy to get your protein fix. There are even entire diets based on upping your protein intake, such as the Atkins diet or the paleo diet.

But what is protein all about anyway? And what benefits does it offer the body?

Dig in here.

What Is Protein? And Why Do I Need It?

Protein is considered the building block of life and is found in every cell of the body. (2)

Protein is made up of amino acids that are attached to one another in long chains. There are 20 different kinds of amino acids, and the sequence in which the different amino acids are arranged helps determine the role of that particular protein. (3)

Proteins play a role in: (2,3)

  • Transporting molecules throughout the body
  • Helping repair cells and make new ones
  • Protecting the body from viruses and bacteria
  • Promoting proper growth and development in children, teenagers, and pregnant women

Without filling your diet with appropriate amounts of protein, you run the risk of missing out on those key functions. Eventually, that could lead to problems, such as a loss of muscle mass, failure to grow, weakened functioning of the heart and lungs, and even early death. (4)

How Much Protein Do I Need for Optimal Health?

Essential amino acids (the ones your body can’t make on its own and needs to get from food) can be found in the food you eat. (2) To source them, you need to fill your diet with a variety of protein-rich foods, which isn’t hard to do since protein is naturally found in many nutritious foods — many of which are likely already part of your regular diet. When you eat, your body will take the protein from the food and break it down into amino acids that can be used by the body. (2)

How to Calculate Your Recommended Protein Intake

The Recommended Dietary Allowance (the amount to meet the nutritional needs of almost all healthy people) is 0.8 grams (g) of protein per kilogram (kg) of body weight. To maintain nutritional balance, the U.S. Department of Agriculture’s MyPlate guidelines recommends protein make up about a quarter of your plate.

To calculate the target number of grams of protein you should eat each day, take your body weight in pounds and multiply it by 0.36. (5) The result should get you within the recommendation to source 10 to 35 percent of your daily total calories from protein. (2) Usually that means at each meal having a piece of meat the size of a deck of cards — that’s 3 ounces (oz) — or the equivalent amount of plant-based protein at lunch and dinner. (6) Plant sources of protein include lentils, beans, nuts, tempeh, and quinoa.

Keep in mind that these recommendations may change depending on age and health. (2) The recommendation changes for athletes, too. People who exercise frequently or are training for a race need to increase their protein intake to between 1.1 and 1.7 g per kg of body weight daily. Anything over 2 g per kg of weight is considered excessive. (6)

Is the Myth That Americans Don’t Get Enough Protein True?

There’s a commonly held belief that Americans don’t get enough protein from their diets. A quick walk through the grocery store reveals hundreds of products that are marketed as “great sources of protein.” The number of protein callouts is so excessive, you’d think there was a major protein deficiency in our country.

Not so. The average American gets about 14 to 16 percent of their calories from protein, which falls within that 10 to 35 percent sweet spot. While Americans typically get more than the recommended amount of  protein, it’s not excessive. (6,7)

That said, Americans don’t always get the types of proteins that nutritionists recommend. The Dietary Guidelines for Americans 2020–2025 found that while three-fourths of Americans meet or exceed the recommended amount of meats, poultry, and eggs, almost 90 percent don’t get enough seafood, and half need more nuts, seeds, and soy products. (8)

Symptoms of Protein Deficiency and Health Risks of Not Getting Enough

Protein deficiency occurs when you don’t eat enough protein. The most severe cases result in a form of malnutrition called kwashiorkor. Usually, this affects people in very poor countries that don’t have enough food to sufficiently feed the people. It rarely occurs in the United States, and when it does, it’s usually linked to some kind of abuse. (9)

Symptoms of protein deficiency include: (10)

  • Delayed growth
  • Loss of muscle mass
  • Thinning hair
  • Edema, which is swelling that results from excess fluid inside the body’s tissues

Although it’s not likely for Americans to be deficient, those who follow certain types of diets need to pay attention to their protein intake. Vegans and vegetarians in particular have to make sure they’re sourcing enough of the macronutrient. Meat is such an abundant source of protein that forgoing meat means these eaters will need to find protein elsewhere. Luckily, there are plenty of plant-based protein sources, including beans, nuts (such as walnuts, pecans, or almonds), and tofu, to make it easy for non–meat eaters to get their fill. Dairy foods are also rich sources of protein for vegetarians. (2)

Another group of people who may have protein concerns: older adults in nursing homes. Perhaps half of them may be protein deficient. (9)

The Role of Protein in Weight Loss and Weight Maintenance

One of the reasons protein is so popular and the cornerstone of many buzzed-about diets is because of its potential link to weight loss.

Over the past two decades, countless studies, including one in the American Journal of Clinical Nutrition, have shown that protein may help people lose weight or maintain weight loss because: (12)

  • Consuming more protein has a positive impact on resting metabolism.
  • High-protein foods increase feelings of fullness. As a result, people eating a sufficient amount of protein may take in fewer calories over the course of the day and lose weight if they end up at a calorie deficit.

To be specific, researchers have found diets that contain between 1.2 and 1.6 g of protein per kg of weight each day — and about 25 to 30 g of protein per meal — have been shown to help with body weight management. (12)

The Best Sources of Protein, From Foods to Supplements

As mentioned, if you live in the United States, you’re probably already getting enough protein in your diet. But if you’re concerned, explore the different ways you can increase how much you get here.

10 Foods That Offer Good Sources of Protein

You can easily up your intake of protein by changing what’s on your plate. The percentages listed here are based on the daily value (DV) of 50 g of protein per day (that’s an estimate of how much an average adult needs):

  • ½ cup nonfat Greek yogurt (23 percent DV)
  • 3 oz tilapia (46 percent DV) (14)
  • ½ cup chickpeas (14.5 percent DV) (15)
  • 3 oz chicken breast (55 percent DV) (16)
  • ½ cup cooked black beans (15.24 percent DV) (17)
  • 2 tablespoons peanut butter (14 percent DV) (18)
  • egg (12 percent DV) (19)
  • 1 ounce almonds (12 percent DV) (20)
  • ½ cup dry unflavored oatmeal (10 percent DV) (21)
  • ½ cup cooked quinoa (8.14 percent DV) (22)

When you’re choosing your protein source, be sure to pay attention to the food’s fat content. Skinless poultry and fish, for instance, are better choices than red meat because they don’t have high levels of saturated fat, which can be dangerous in excess because it can increase the LDL, or “bad” cholesterol in your blood. (23)

Top Sources of Protein Beyond Whole Foods

Even though protein is found in many whole foods, there are hundreds of manufactured protein-packed items. Protein powders, protein energy bars, and even protein-boosted breads, pancake mixes, and chips are available to you.

These products may be appropriate for certain people who are supposed to take in more protein than the usual recommendation. Athletes, for instance, may benefit from ingesting protein within an hour of working out. (6) A study published in the American Journal of Clinical Nutrition showed that a large single dose of 25 g of protein after exercise can increase muscle protein synthesis. (24) That could explain why protein shakes are so often associated with body builders and gym rats.

Elderly people who have trouble eating and drinking enough protein during the day, sometimes as a result of a decreased appetite, can also benefit from high-protein products and shakes, according to an article published in the magazine Aging Well. (25) Protein is important for this group because the body’s protein stores naturally decline as people age. (25) A report in The Journal of Post-Acute and Long-Term Care Medicine recommends that those over the age of 65 get an average daily intake between 1.0 to 1.2 g protein per kilogram of body weight. (26) Without enough protein, these older adults may experience general weakness (including an increased risk of falling), fatigue, decreased mobility, and weakened immune systems. (25)

Here’s the fix: Taking in 25 to 30 g of high-quality protein per meal can help stimulate protein synthesis for these older adults. (26) Protein supplements can be especially helpful in hospitals and can reduce the risk of developing pressure ulcers. (25)

Word to the wise: Study the nutrition label before digging into protein shakes and other supplements. Just because a product is high in protein doesn’t necessarily make it healthy all around. Look for protein supplements that are no more than 200 calories, have fewer than 2 g of saturated fat, and no more than 5 g of sugar. (6)

Also, because supplements aren’t regulated by the Food and Drug Administration (FDA), there’s no oversight checking to make sure the products live up to the claims on their packaging, so take these with a grain of salt and be sure to talk to your healthcare team before adding them to your diet. (27)

Experts say it’s a good idea to lean on whole foods rather than processed foods to source your protein, as whole foods offer nutritional benefits that the man-made options don’t provide. (6)

Side Effects and Health Risks of Getting Too Much Protein

Protein comes with a host of health benefits, but it is possible to overdo it. Many people pay attention to the benefits of protein and figure there’s no harm in stocking up. The problem is that the body doesn’t know what to do with the excess amounts of protein, and it could end up harming the bones, kidneys, and liver, according to a review published in the journal ISRN Nutrition. (28)

Experts say a high-protein meal with about 40 g of protein doesn’t benefit the body any more than one with 15 to 25 g of protein would, so there’s no upside to going overboard. (6)

There are, on the other hand, a few potential downsides. Too much protein can lead to: (28)

  • Kidney stones
  • Bone loss
  • Too much calcium in the bloodstream
  • Liver complications

Meat-heavy diets (which are high in protein), such as the carnivore diet, can also be dangerous and increase one’s risk of developing coronary heart disease and cancer, particularly breast, bowel, and prostate cancers. (28)

Protein and Food Allergies: What to Know

Food allergies occur when the body’s immune system attacks certain food proteins. (29) Your body will fight back by making its own proteins, called IgE antibodies, or immunoglobulin E. If you have an allergy to a certain protein, the next time you eat or drink something containing that protein, you’ll experience an allergic reaction, such as itchiness or trouble breathing. (29)

Many of the most common food allergies are associated with foods that are high in protein, such as eggs, peanuts, tree nuts, and fish. (29)

The 3 Top-Selling Protein Powders on Amazon

Protein powders are incredibly popular. The top three protein powders sold on Amazon based on customer reviews are:

  • TGS Whey Protein Powder; $32.39; Amazon
  • SFH Fuel Whey Protein Powder; $58.89; Amazon
  • RENEW Multi Collagen Protein Powder; $18.99; Amazon

Editorial Sources and Fact-Checking

  1. Macronutrients. USDA National Agricultural Library.
  2. Protein in Diet. MedlinePlus. June 8, 2021.
  3. What Are Proteins and What Do They Do? MedlinePlus. March 26, 2021.
  4. Protein. Harvard T.H. Chan School of Public Health.
  5. How Much Protein Do You Need Every Day? Harvard Health Publishing. July 19, 2022.
  6. Are You Getting Too Much Protein? Mayo Clinic. February 23, 2017.
  7. Berryman CE, Lieberman HR, Fulgoni 3rd VL, et al. Protein Intake Trends and Conformity With the Dietary Reference Intakes in the United States: Analysis of the National Health and Nutrition Examination Survey, 2001–2014. The American Journal of Clinical Nutrition. August 1, 2018.
  8. Dietary Guidelines for Americans 2020–2025 [PDF]. U.S. Department of Agriculture.
  9. Kwashiorkor. MedlinePlus. February 24, 2022.
  10. Protein and Amino Acids. Recommended Dietary Allowances: 10th Edition. 1989.
  11. Deleted, July 23, 2022.
  12. Hansen TT, Astrup A, Sjödin A. Are Dietary Proteins the Key to Successful Body Weight Management? A Systematic Review and Meta-Analysis of Studies Assessing Body Weight Outcomes After Interventions With Increased Dietary Protein. Nutrients. September 2021.
  13. Deleted, July 23, 2022.
  14. Fish, Tilapia, Cooked, Dry Heat. U.S. Department of Agriculture. April 1, 2019.
  15. Chickpeas (Garbanzo Beans, Bengal Gram), Mature Seeds, Cooked, Boiled, Without Salt. U.S. Department of Agriculture. April 1, 2019.
  16. UPDATE: Chicken, Broiler  or  Fryers, Breast, Skinless, Boneless, Meat Only, Cooked, Braised. U.S. Department of Agriculture.
    April 1, 2019.
  17. Beans, Black, Mature Seeds, Cooked, Boiled, Without Salt. U.S. Department of Agriculture. April 1, 2019.
  18. Peanut Butter, Smooth Style, Without Salt. U.S. Department of Agriculture. April 1, 2019.
  19. Egg, Whole, Raw. U.S. Department of Agriculture. April 1, 2019.
  20. Nuts, Almonds. U.S. Department of Agriculture. April 1, 2019.
  21. Cereals, Quaker, Quaker MultiGrain Oatmeal, Dry. U.S. Department of Agriculture. April 1, 2019.
  22. Quinoa, Cooked. U.S. Department of Agriculture. April 1, 2019.
  23. Saturated Fat. American Heart Association. November 1, 2021.
  24. West DWD, Burd NA, Coffey VG, et al. Rapid Aminoacidemia Enhances Myofibrillar Protein Synthesis and Anabolic Intramuscular Signaling Responses After Resistance Exercise. American Journal of Clinical Nutrition. September 2011.
  25. Ensuring Adequate Protein Intake. Aging Well. Summer 2011.
  26. Bauer J, Biolo G, Cederholm, T, et al. Evidence-Based Recommendations for Optimal Dietary Protein Intake in Older People: A Position Paper From the PROT-AGE Study Group. The Journal of Post-Acute and Long-Term Care. July 18, 2013.
  27. FDA 101: Dietary Supplements. U.S. Food and Drug Administration. June 2, 2022.
  28. Delimaris I. Adverse Effects Associated With Protein Intake Above the Recommended Dietary Allowance for Adults. ISRN Nutrition. July 18, 2013.
  29. What Is a Food Allergy? Food Allergy Research & Education.

Additional Sources

  • Coelho-Júnior HJ, Rodrigues B, Uchida M, et al. Low Protein Intake Is Associated With Frailty in Older Adults: A Systematic Review and Meta-Analysis of Observational Studies. Nutrients. September 2018.
  • Hansen TT, Astrup A, Sjöodin A. Are Dietary Proteins the Key to Successful Body Weight Management? A Systematic Review and Meta-Analysis of Studies Assessing Body Weight Outcomes After Interventions With Increased Dietary Protein. Nutrients. September 2021.

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