Protein is one of the three nutrients found in food that the body requires in large amounts. Along with carbohydrates and fat, protein is essential for the human body.
Proteins are made of small compounds called amino acids. There are hundreds of amino acids that exist in nature, but the human body only utilizes 22 of them.
The human body can produce all but nine of the amino acids that it needs. These nine are called essential amino acids and must be consumed through food.
All foods contain differing combinations of amino acids, making a balanced diet essential. In general, animal proteins like meat, dairy, and eggs contain all the essential amino acids.
Plant-based proteins from foods like beans, grains, nuts, and soy are rich in some amino acids but may be lacking in others. This lack underlines the need for a well-balanced diet with variety.
What does protein do?
Protein is the major building block of the human body. Its main job is to build and maintain tissue.
Many foods are high in protein, including several that are suitable for vegetarians and vegans.
Periods of growth, such as infancy, childhood, and pregnancy, require more protein for this growth to occur. Protein needs are also increased for the following people:
- People with injuries
- People who have undergone surgery
- Active people who are consistently breaking down muscle during exercise
The total amount of protein that is consumed in a day is not nearly as important as how protein intake is spread out over the day.
Many people will consume a small amount of protein at breakfast, a moderate amount at lunch, and a large amount at dinner.
A typical day's eating might involve 10 grams of protein or less at breakfast (cereal), 25 grams at lunch (sandwich), 5 grams for a snack (granola bar), and 40 grams at dinner (chicken or beef).
However, the body can only absorb and use a certain amount protein at one time. The body uses what it can and then what is left over becomes waste. So, it is better for people to spread 60 grams of protein over three or four meals of 15-20 grams each instead of having 60 grams of protein in one meal.
How much protein is needed each day?
There is a certain amount of protein people can aim for to make sure they are they get the most protein use, muscle generation, and recovery every time they eat. This amount depends on the person's body size and how active they are.
Half a block of tofu contains 18 grams of protein.
A 6-foot, 250-pound man who strength trains five times a week can absorb and utilize more protein than a 5-foot female who does not exercise much. Studies to date have suggested a 20-30 gram per meal protein goal, but more research is needed.
The Recommended Dietary Allowance (RDA) for protein is 0.8 grams per kilogram of body weight per day. The RDA is the minimum amount of protein needed for meeting nutritional requirements, not the maximum.
Endurance athletes need 1.2 to 1.4 grams per kilogram of body weight. Strength training or power athletes require 1.2 to 1.7 grams per kilogram of body weight. The more physically active a person is, the more protein that they will need to consume.
Some research has recommended as much as 2 grams per kilogram of body weight to prevent muscle loss in athletes who want to lose weight and have reduced the amount of calories they consume.
Amount of protein in common food sources
According to the U.S. Department of Agriculture, the following amounts of protein can be found in common sources of food:
|Food||Amount||Grams of protein|
|Ground beef||3 ounces||21|
|Black beans||¾ cup||11.43|
|Peanut butter||2 tablespoons||8|
Risks and precautions for consuming protein
Most studies support an intake of up to 2 grams per kilogram of body weight without any negative or adverse effects (including kidney damage). Consuming more than 2.5 grams of protein per kilogram of body weight can increase the risk of the following:
- Taking in too many calories
- Passing out higher levels of the nutrient calcium in the urine
Eating more than 200 to 400 grams of protein per day can exceed the liver's ability to convert excess nitrogen to a waste product called urea. This can lead to nausea, diarrhea, and other adverse side effects.