What is it?
Proteins are the building blocks that grow and repair your body. Proteins are needed not only for muscle but also for hair, skin and internal organs. Some proteins travel around your body in the blood as hormones, enzymes and red blood cells. Protein is unique because it is the only food source of nitrogen, which is essential to all plant and animal life.

Proteins are made up of chains of amino acids. For each protein, there are specific amino acids in a specific amount, and they are joined in a unique order. This is what makes a chicken different from cheese or a fingernail different from a strand of hair. There are 22 amino acids. Eight of these are called the essential amino acids because they cannot be made by the body and must be provided by the diet.

What does it do?

• Antibodies, which are made of protein, help you resist disease and infection.
• Each day, your body loses protein in the form of hair, skin and nails. You also use up protein in all the activities of running and maintaining your body.
• If you eat protein daily, it is supplied to your body tissue to replenish any loss and repair any injury.
• For growing infants, children and teens, protein, along with sufficient calories, is necessary for growth of the entire body.
• Pregnant and breast-feeding women need adequate protein for the fetus, for supporting maternal tissue, and for the production of breast milk after delivery.
• If you have a cut, undergo surgery, or have an injury or illness, you need protein to recover and to rebuild your body.

Where do you get it?
Protein foods are classified in two ways: complete and incomplete. Complete proteins, which come from animal sources such as chicken, fish, dairy and soybeans, contain all the essential amino acids that help build your muscle and body tissue. Incomplete proteins, found in plant foods, such as grains, seeds, nuts, beans and vegetables, provide a varying but limited array of amino acids. A greater variety and amount of incomplete proteins must be consumed to cover all the amino acids needed for protein building.

We can compensate for the amino acid deficiencies in an incomplete protein by combining it with another protein, thus providing all the building blocks for protein creation. This is the concept of complementary proteins, in which proteins with opposite strengths and weaknesses complement each other.

For example, many cereals are low in an amino acid called lysine, but high in methionine and cystine. Lima beans, soybeans and kidney beans are high in lysine but low in methionine and cystine. Many cultures, including Mexican and Indian cultures, have limited animal protein sources but eat combinations of incomplete foods. Examples of appropriate combinations include:

• rice and beans
• cereal and milk
• beans and corn
• bread and cheese