While carbohydrates are located at the base of the food pyramid, proteins occupy the smaller space in the middle of the pyramid. Protein-rich foods include beef, poultry, fish, beans, eggs, nuts, and dairy products such as milk, yogurt, and cheese. Your body requires proteins for a wide variety of processes. Proteins are important structural components of cells. In fact, they make up half the dry weight of a cell—muscles are largely composed of proteins. Proteins called enzymes help regulate all the chemical reactions that build up and break down molecules inside your cells. Proteins also function as hormones that send chemical messages throughout your body. A healthful diet will obtain about 15% of its Calories from protein.
Proteins are large molecules made of monomer subunits called amino acids. There are 20 commonly occurring amino acids. Like carbohydrates, amino acids are made of carbons, hydrogens, and oxygens, but they have an additional amino group and various side groups. Side groups are chemical groups that give amino acids different chemical properties.
Polymers of amino acids are sometimes called polypeptides because the name for the chemical bond joining adjacent amino acids is a peptide bond. Different amino acids are joined together to produce different proteins in much the same manner that children can use differently shaped beads to produce different structures. Each amino acid has unique chemical properties. Since different proteins are composed of different amino acids, each protein has unique chemical properties. Your body synthesizes most of the amino acids it needs. Those your body cannot synthesize are called essential amino acids and must be supplied by the foods you eat. Complete proteins contain he essential amino acids your body need—proteins obtained by eating meat are more likely to be complete than those obtained by eating plants; plant proteins can often be missing one or more essential amino acids.
In the past, some nutritionists believed that vegetarians might be at risk for deficiencies in certain amino acids. However, scientific studies have shown that there is little cause for concern. If a vegetarian’s diet is rich in a wide variety of plant-based foods, the body will have little trouble obtaining all the amino acids it needs to build proteins.
A more contemporary issue is whether vegetarians are deficient in vitamin. This vitamin is required for the production of red blood cells and helps maintain proper nerve function. Vegetarians can increase their intake by drinking soy milk or taking vitamin supplements.
Even though it is possible to obtain all the proteins you need by eating a variety of plants, Americans tend to eat a lot of meat as well. In addition to being rich in proteins, meat tends to be rich in fat.