Alternate Names: Diet - protein; Nonessential protein; Essential protein
Food Sources: Proteins are described as essential and nonessential proteins or amino acids. The human body requires approximately 20 amino acids for the synthesis of its proteins. The body can make only 13 of the amino acids; these are known as the nonessential amino acids. They are, in fact, essential but people do not have to get them from food we eat. There are 9 essential amino acids that are obtained only from food, and not made in the body.
If the protein in a food supplies enough of the essential amino acids, it is called a complete protein. If the protein of a food does not supply all the essential amino acids, it is called an incomplete protein.
All meat and other animal products are sources of complete proteins. These include beef, lamb, pork, poultry, fish, shellfish, eggs, milk, and milk products.
Protein in foods such as grains, fruits, and vegetables are either low incomplete protein or lack one of the essential amino acids. These food sources are considered incomplete proteins. Plant proteins can be combined to include all of the essential amino acids and form a complete protein. Examples of combined, complete plant proteins are rice and beans, milk and wheat cereal, and corn and beans.
Functions: Protein is the main component of muscles, organs, and glands. Every living cell and all body fluids, except bile and urine, contain protein. The cells of muscles, tendons, and ligaments are maintained with protein. Children and adolescents require protein for growth and development.
Recommendations: The body does not make more protein than usual when dietary protein is increased. The extra protein is broken down in the body and the amino acids are used for energy or turned into fat. A nutritionally balanced diet provides adequate protein. Even vegetarians are able to get enough protein if they eat the proper combination of plant proteins.
The amount of protein eaten normally in the United States is more than is recommended. Approximately 20% of the total daily calories should come from protein. Two to three servings of protein-rich food will meet the daily needs of most adults.
The following are the recommended serving sizes for protein:
- For recommended serving sizes of protein for children and adolescents see Diet for Age.
- 2 to 3 ounces of cooked lean meat, poultry, and fish (a portion about the size of a deck of playing cards)
- 1/2 cup of cooked dry beans, lentils, or legumes
- 1 egg or 2 tablespoons of peanut butter, which count as 1 ounce of lean meat
Select lean meat, poultry without skin, fish, and dry beans, lentils, and legumes often. These are the protein choices that are the lowest in fat. For more information, see the food guide pyramid.
Side Effects: A diet high in meat could cause an excessive saturated fat and cholesterol intake. Another potential problem is that a high-protein diet may put a strain on the kidneys. Extra waste matter, which is the end product of protein metabolism, is excreted in the urine.
