Proteins are the building blocks of life. Every cell in the human body contains protein. The basic structure of protein is a chain of amino acids.
You need protein in your diet to help your body repair cells and make new ones. Protein is also important for growth and development in children, teens, and pregnant women.
Diet - protein; Complete protein; Incomplete protein
Protein foods are broken down into parts called amino acids during digestion. The human body needs a number of amino acids in large enough amounts to maintain good health.
Amino acids are found in animal sources such as meats, milk, fish, and eggs. They are also found in plant sources such as soy, beans, legumes, nut butters, and some grains (such as wheat germ and quinoa). You do not need to eat animal products to get all the protein you need in your diet.
Amino acids are classified into three groups:
Essential amino acids cannot be made by the body, and must be supplied by food. They do not need to be eaten at one meal. The balance over the whole day is more important.
Nonessential amino acids are made by the body from essential amino acids or in the normal breakdown of proteins.
Conditional amino acids are needed in times of illness and stress.
A well-balanced diet provides enough protein. Healthy people rarely need protein supplements.
Vegetarians are able to get enough essential amino by eating a variety of plant proteins.
The amount of recommended daily protein depends upon your age and health. Two to three servings of protein-rich foods will meet the daily needs of most adults.
The following are the recommended serving sizes for protein:
2 to 3 ounces of cooked lean meat, poultry, or fish (a portion about the size of a deck of playing cards)
1/2 cup of cooked dried beans
1 egg, 2 tablespoons of peanut butter, or 1 ounce of cheese
Children and teens may need different amounts, depending on their age. Some healthy sources of meat protein include:
Turkey or chicken with the skin removed, or bison (also called buffalo meat)
Lean cuts of beef or pork, such as round, top sirloin, or tenderloin (trim away any visible fat)
Fish or shellfish
Other good sources of protein include:
Pinto beans, black beans, kidney beans, lentils, split peas, or garbanzo beans
Nuts and seeds, including almonds, hazelnuts, mixed nuts, peanuts, peanut butter, sunflower seeds, or walnuts (just watch how much you eat, because nuts are high in fat)
Tofu, tempeh, and other soy protein products
Low-fat dairy products
Do not eat more than four eggs per week. Eggs are very high in cholesterol. Try recipes that use egg whites only.
The U.S. Department of Agriculture's newest food guide, called MyPlate, can help you make healthy eating choices.
Escott-Stump S. Nutrition and Diagnosis-Related Care. 6th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2008.
United States Department of Agriculture. Center for Nutrition Policy and Promotion. Dietary Guidelines for Americans. 2010. National Academy Press, Washington, DC, 2010.
National Academy of Sciences. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academy Press. Washington, DC, 2005.
Alison Evert, MS, RD, CDE, Nutritionist, University of Washington Medical Center Diabetes Care Center, Seattle, Washington. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.