What Is Protein? A Complete Scientific Guide

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), according to the U.S. Department of Agriculture (USDA).

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.

Protein is considered the building block of life and is found in every cell of the body, according to MedlinePlus.

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, per MedlinePlus.

As MedlinePlus notes, proteins play a role in:

• 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. According to the Harvard T.H. Chan School of Public Health, that eventually 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.

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 one-quarter of your plate.

To calculate the target number of grams of protein you should eat each day, Harvard Health Publishing says take your body weight in pounds and multiply it by 0.36. The result should get you within the recommendation to source 10 to 35 percent of your daily total calories from protein, according to MedlinePlus. Usually that means having some kind of dairy at each meal plus 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, according to Mayo Clinic.

Keep in mind that these recommendations may change depending on age and health. 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.

Certain people may benefit from focusing on adding protein to their diet.

Athletes

Have some hefty fitness goals? Athletes may benefit from ingesting protein within an hour of working out, according to Mayo Clinic. Previous research showed that a large single dose of 25 g of protein after exercise can increase muscle protein synthesis. That could explain why protein shakes are so often associated with body builders and gym rats.

Elderly People 

With age, you may take in fewer calories during the day and lose weight as a result, according to an article published in April 2021 in Nutrients. Many elderly people benefit from supplementing with protein products and shakes since a significant portion of this weight loss is muscle. Indeed, people lose 3 to 8 percent of their lean muscle mass each decade after age 30, per previous research. Without enough protein, these older adults may experience general frailty, fatigue, decreased muscle strength, and higher mortality risk, the Nutrients article notes.

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, according to Mayo Clinic.

Protein deficiency happens when you don’t eat enough protein.

Prevalence

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. According to Harvard Health Publishing, the average American gets about 15 percent of their calories from protein, which falls within that 10 to 35 percent sweet spot. And in fact, as the Mayo Clinic notes, most Americans get 2 times as much protein as they need.

Signs and Symptoms

According to previous research, symptoms of protein deficiency include:

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

Prevention

Preventing protein deficiency may be a worthwhile effort for people on extreme fad diets or people who are following an imbalanced plant-based diet. To address the latter concern, check out plant-based protein sources, including beans, nuts (such as walnuts, pecans, or almonds), and tofu. Dairy foods are also rich sources of protein for vegetarians.

Consequences

The most severe cases of protein deficiency result in a form of malnutrition called kwashiorkor, according to MedlinePlus. 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.

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

But the real relationship between protein and weight loss may surprise you. The truth is, protein intake can help you lose weight — but not all protein sources are equal in this regard.

According to a previous study published in The New England Journal of Medicine that analyzed the eating habits of more than 120,000 men and women during a period of 20 years, healthy protein sources helped with healthy weight control, while unhealthy sources did not. Healthy sources included nuts, while unhealthy sources included processed and red meat.

Among those study participants, those who opted for low-fat and plant-based sources of protein, such as low-fat cheese and chicken without skin, as well as walnuts, were less likely to gain weight than those who ate chicken with skin and full-fat cheese. Those findings were published in April 2105 in the American Journal of Clinical Nutrition.

The bottom line: Protein is not a magic bullet for weight loss. But choosing healthier sources of the macronutrient — that is, those that are whole, low in fat, and especially plant-based — appear to support this effort.

If you’re concerned about your protein intake, here are some top sources to keep in mind.

Foods That Are 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):

• 1 cup nonfat Greek yogurt (excellent source of protein)
• 3 oz tilapia (excellent source of protein)
• ½ cup chickpeas (excellent source of protein)
• 3 oz chicken breast (excellent source of protein)
• ½ cup cooked black beans (good source of protein)
• 2 tablespoons peanut butter (good source of protein)
• 1 egg (good source of protein)
• ¼ cup almonds (good source of protein)
• ½ cup unflavored oatmeal (good source of protein)

When you’re choosing your protein source, pay attention to 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, according to the American Heart Association.

Protein Supplements and Protein-Fortified Products

Although protein is found in many whole foods, there are numerous manufactured protein-packed items at your disposal. Here are some examples:

• Protein powder supplements
• Protein shakes
• Protein bars
• Protein breads
• Protein pancake mixes
• Protein chips

These products may be appropriate for certain people who are aiming to take in more protein than the usual recommendation, such as athletes and elderly people.

Here’s what to keep in mind before reaching for these products:

• Study your food’s Nutrition Facts 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, Mayo Clinic recommends.
• Know that supplements may be risky. This is especially true if you have an existing health condition and are taking medication. More fundamentally, keep in mind that because the U.S. Food and Drug Administration (FDA) doesn’t regulate supplements, 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. No matter what, talk to your healthcare team before adding them to your diet.
• Don’t think of high-protein packaged products as a replacement for whole-food sources of protein. Whole foods offer nutritional benefits that the man-made options don’t provide, per the Mayo Clinic. Not to mention, health experts recommend limiting packaged, processed foods in the diet for optimal health.

Although protein is generally healthy, it’s 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 previous review.

Experts say that for most people, 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.

There are, on the other hand, a few potential downsides. The aforementioned review notes that too much protein can lead to:

• 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, according to the same review mentioned earlier.

According to Food Allergy Research and Education, food allergies happen when the body’s immune system attacks certain food proteins. 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.

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

Protein is one of three macronutrients your body needs to perform at its best. You can add protein to your diet via high-protein foods and products like protein powders, but there’s an excellent chance you’re getting enough protein already if you live in the United States. Also, take note that it’s possible to overdo it on protein, which can increase the risk for health issues including kidney stones.