Protein belongs to a class of nutrients called macronutrients, which provide you with calories. Protein also provides the structural support to most your cells. It helps transport substances throughout your body, maintains acid-base balance, contributes to the synthesis of enzymes and hormones and allows your immune system to create antibodies.
Amino Acids
Amino acids are the building blocks of the proteins in foods. Each amino acid consists of carbon, hydrogen, oxygen and nitrogen and contains an acid group, amine group and unique side chain that gives the amino acid its specific qualities. There are a total of 20 different amino acids that your body combines in variety of different ways to synthesize the specific types of protein that it needs. Eleven of these amino acids are nonessential, meaning you do not need to consume them in your diet because your body is able to synthesize them. The remaining 9 amino acids are essential, so you must consume them in your diet because your body cannot make them.
Amino Acids and Protein
Different amino acids are joined together by a bond called a peptide bond to create a protein. Proteins usually contain between 100 and 10,000 amino acids joined together, according to "Nutrition and You" by Joan Salge Blake. The amino acid content determines which type of protein is made.
Types of Protein
Proteins are categorized into two major types based on which amino acids they contain, or their amino acid profile. A protein that provides all of the essential amino acids, as well as some of the nonessential amino acids is called a complete protein. Most animal foods are complete proteins, but a protein that is low or missing one or more of the essential amino acids is called an incomplete protein. The missing amino acid or the amino acid that is lowest in quantity in an incomplete protein is referred to as a limiting amino acid. Most incomplete proteins are those in plant foods. A complete protein is generally regarded as a higher quality protein than an incomplete protein.
Complementary Proteins
When incomplete proteins are eaten with complete proteins or other incomplete proteins that contain their limiting amino acid, these proteins are referred to as complementary proteins. In combination, complementary proteins contain a complete amino acid profile and are considered a complete protein. "Nutrition and You" by Joan Salge Blake notes that it is not necessary to consume complementary proteins in the same meal. As long as you consume them in the same day, your amino acid needs are met. One of the best complementary proteins are rice and beans.
References
- "Nutrition and You"; Joan Salge Blake; 2008
- Kids Health: Learning About Proteins
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