Dietary proteins are powerful nutrients that build and repair body tissue. Proteins speed up chemical reactions in the body, serve as chemical messengers, fight infection, and transport oxygen from the lungs to the body's tissues. Protein provides 4 calories of energy per gram, the body uses protein for energy only if carbohydrate and fat intake is insufficient.

Proteins are made of smaller units called amino acids. The digestive tract breaks dietary protein into amino acids and are absorbed into the bloodstream and sent to the cells that need them, amino acids then recombine into the functional proteins our bodies need. Of the more than 20 amino acids our bodies require, eight to nine cannot be made by the body in sufficient quantities to maintain health. These amino acids are considered essential and must be obtained from food.

Animal proteins, eggs, milk, meat, fish, and poultry, are considered complete proteins and contain all of the essential amino acids our bodies need. Plant proteins, vegetables, grains, and beans, lack one or more of the essential amino acids. However, plant proteins can be combined in the diet to provide all of the essential amino acids.

Experts recommend that protein intake make up only 10 percent of our daily calorie intake. Extra amino acids cannot be stored for later use, the body destroys these amino acids and excretes their by-products. Deficiencies in protein consumption may result in the health problems marasmus and kwashiorkor the two most common forms of protein malnutrition.

Some health conditions place an enormous demand on the body as it builds tissue or fights infection, and these conditions require an increase in protein consumption.