The human structure is primarily composed of protein. Protein contains nitrogen, enabling it to be used in the production of cells, tissues, muscles and skin. Dietary protein is essential to build new and repair damaged tissue. Proteins are composed of amino acids, which determine how the protein will be used in the body. The ability to synthesize specific proteins depends on the availability of all necessary amino acids. Therefore, the amount and quality of dietary protein is important to health.
Identification
Protein metabolism is the chemical process used by the body to break down dietary or endogenous proteins into amino acids. Ingested dietary proteins are digested into amino acids and absorbed into the bloodstream. These amino acids are then used to synthesize new proteins or can be used as an energy source. DNA carries the instructions for building cells and tissue. This information is expressed by combining specific amino acids into unique proteins.
Amino Acids
The synthesis of a new protein requires the presence of all necessary amino acids. Amino acids have the same general structure with unique side chains determining the identity and function of each. They are much like letters in the alphabet that can be combined to form unique "words" or proteins. Nonessential amino acids can be produced by our bodies. Eight, however, are essential amino acids that can only be obtained from the diet.
Protein Functions
Proteins are needed to make, repair and maintain all tissues of the body. Proteins compose cells and they also help regulate cell function. Proteins function as enzymes used to speed up biological reactions. Protein can be used as an energy source, but it is not as efficient of a fuel as carbohydrates and fat.
Protein Quality
The quality of a protein is determined by its amino acid makeup and the bioavailability of those amino acids. A quality score is calculated by comparing the amino acids in the protein to human needs. The amino acid in shortest supply is considered the limiting amino acid. Digestibility of a protein is also a major factor affecting quality. Meat is a complete protein, meaning it contains all the needed amino acids. Plant proteins are not considered complete, but vegetarian diets can be planned to include all essential amino acids.
Protein Requirements
According to recommendations by the Institute of Medicine, a healthy adult maintaining a healthy weight requires 0.8 g of protein per kg. Dietary protein should make up between 10 and 15 percent of total energy intake to meet requirements. Extra protein is needed during times of disease, growth and healing after surgery or an injury.
References
- University of South Australia: Protein Metabolism
- "Natural Health Natural Medicine"; Andrew Weil, M.D.; 2004
- "Krause's Food & Nutrition Therapy"; L. Kathleen Mahan, Sylvia Escott-Stump; 2008
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