Definition
Proteins are complex organic compounds. The basic structure of protein is a chain of amino acids.
Alternative Names
Diet - protein; Complete protein; Incomplete protein
Function
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.
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 called non-essential because the body can make them and does not need to get them from the diet. 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.
Side Effects
A diet high in meat could lead to high cholesterol or other diseases, such as gout. 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.
Recommendations
A nutritionally balanced diet provides adequate protein. Vegetarians are able to get enough protein if they eat the proper combination of plant proteins.
The amount of recommended daily protein depends upon age, medical conditions, and the type of diet one is following. 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 age appropriate diet for children
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.
