When talking about “weight loss,” fat and carbs have their fair share of haters, but protein is always getting good press.  Protein is an essential nutrient for strong bones, muscles, skin, and pretty much every other part of the body. When consumed, your body breaks down the protein into amino acids to help transport molecules throughout the body, stimulate muscle growth, and increase metabolism. 

But if that means more protein is always better? To figure out that problem, you need to know the principles of how proteins are metabolized and utilized in the body. Here’s what the research and studies show.

Why is Protein Important

Protein is found throughout the body and is a component of every cell.

• Tissue building is the primary function of the protein. It is an essential building block of all bones, muscles, cartilage, hair, and skin. 
• Protein also helps repair body tissues, infection-fighting, blood clotting, and wound healing. 
• It is the necessary raw material from which your body makes the enzymes critical for promoting stomach acid and aiding digestion.
• Red blood cells contain a protein compound that helps oxygenate body organs and tissues while supplying nutrients like fats, vitamins, and minerals to the entire body.
• Protein also plays a vital role in hormone regulation.
• Your body needs protein to produce antibodies to fight against viruses, bacteria, and other harmful substances. A high-protein diet can help strengthen your immune system.  

How Much Protein Do We Need Every Day?

From the perspective of nutrients, the recommended daily protein intake by the World Health Organization and the United Nations Agrifood Organization: for a healthy adult is 0.83 grams/kg of body weight per day; for example, for a 60 kg adult, the optical protein intake is 49.3 g per day.

From the perspective of total dietary calories, the dietary guidelines of the United States recommend an acceptable protein intake range of 10%-35% of total calories. An adult diet with a daily intake of 2,000 kcal is 200-700 kcal per day from protein, equivalent to 50-175 grams of protein, which can fully meet the recommended daily intake.

According to MyPlate, there are suggested amounts of proteins for individuals aged two and older who need to eat depending on factors like age, gender, and activity level.

Amount that counts as 1-ounce equivalents in Protein Foods Group

• Meat: 1 ounce of cooked lean beef, pork, or ham.
• Poultry:  1 egg; 1 ounce of chicken or turkey, without skin.
• Seafood: 1 ounce of cooked fish or shellfish.
• Beans: ¼ cup cooked beans.
• Nuts: ½ ounce nuts or seeds; 1 tablespoon peanut butter
• Dairy:  ⅓ cup of Greek yogurt

Where Does the Recommended Protein Intake Come from—Nitrogen Balance Study

Protein and nitrogen(N) are closely related. Fats and carbs contain only carbons, hydrogen, and oxygen. So protein is the only macronutrient containing N—we know roughly 98% of the total body N comes primarily from protein, regardless of one’s health. That’s why N balance is commonly used as a proxy measure of protein balance.

N balance is calculated as the difference between N intake and N losses in urine, stool, skin, and body fluids. When your body is in N balance, the protein-rich tissues, including muscle, won’t be broken down. So the amount of protein people needs daily is defined as the amount of protein that puts most people in N balance.

The N balance test shows that 0.66 g/kg of high-quality protein per day can bring half the population to N balance. We added two standard deviations to get most of the people to N balance, which resulted in the commonly suggested amount of 0.83 g/kg. Since the nitrogen balance test uses high-quality protein, the protein sources in daily life may differ. So the recommended protein intake can be relaxed to about 1.05 g/kd, which can meet the protein needs of almost everyone and put everyone in nitrogen balance [1]. 

Where the Other Protein Goes?

For those who need to be in positive N balance, such as people in a period of growth, in a state of tissue synthesis (pregnant, breastfeeding, or recovering), or crave to increase muscle mass by doing extensive strength training, eating the amount of protein more than recommended can lead to muscle gain. But does that imply the more, the better? 

The body's protein synthesis has a limit. A newborn baby is at the peak of tissue synthesis, and adults, even Olympic-level athletes, find it hard to get their bodies to synthesize more than babies. The daily protein requirement for 0-6 months infants is 2.0 g/kg, so no one needs more than 2.0 g/kg/d of protein in their daily lives. (But in fact, many people eat more than that.)

Many nutritionists and doctors agree that eating more than 2.0 g/kg/d of protein will do more harm than good for healthy individuals. It may cause an extra burden on the kidneys, liver, and bones, as well as potentially increase the risk for heart and kidney disease.

When protein from food enters the body, it is digested and converted to amino acids, which the body can use to synthesize new proteins and renew the body's tissues. When the intake is high, the protein that is not used for synthesis will naturally go the other two ways:

• Be converted into carbohydrates for energy supply or as energy storage (that is, being fat).
• Be excreted from the body by becoming urine.

What Food Contains Protein

Protein can be found in animal sources and plant-based foods. Some foods are considered healthy and excellent sources of protein, including eggs, nuts, lean meats, fish, dairy, and certain grains. Eating plans that include healthy-fat dairy products may help improve blood pressure, heart health, and cholesterol levels.

Here are some options for nutritious high-protein food:

• Poultry: Egg, chicken breast, lean beef, lean pork, turkey breast, lamb, goat, skinless chicken, quail, and duck.
• Seafood: fish, shellfish, salmon, tuna, cod, shrimp, mackerel, lobster, catfish, crab
• Dairy foods: cottage cheese, greek yogurt, milk, cheese.
• Legumes: lentils, beans, split peas, soy.
• Nuts and seeds: almonds, peanuts and peanut butter, quinoa, pumpkin seeds, Ezekiel bread,  chia seeds, walnuts. 

Some high-protein food may also be high in saturated fat. High intake of saturated fat can increase the risk of heart and cardiovascular disease. Thus, limit protein foods high in saturated fats.

The Bottom Line

• The recommended protein intake is derived from nitrogen balance studies.
• An amount of 0.83g/kg/d will fully meet most populations' protein needs.
• There is no proven health benefit to a protein intake of more than 2g/kg/d.

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