Protein In Diet
Protein is made up of smaller units called amino acids. There are 20 different amino acids. The body can only make 13 of them; the other 9 must come from food. These 9 are called "essential" amino acids.
What food source is the nutrient found in?
Animal foods are the best source of "complete" proteins. A "complete" protein contains all nine of the essential amino acids.
"Incomplete" proteins, the type common in plant-based proteins, do not provide the body with all nine essential amino acids.
Plant-based proteins (with the exception of soy foods) do contain essential amino acids but not all nine. Vegetarians, that eat strictly plant foods, should eat a large variety of plant foods daily to make sure they get all of the nine essential amino acids.
Good sources of complete proteins include:
- dairy products
Vegetable foods that are high in protein include all kinds of legumes such as peas, beans, grains and some vegetables. Even though soy foods are plant-based foods, it is the only plant food that contains all nine essential amino acids. It is the only plant food that is a "complete" protein.
How does the nutrient affect the body?
Protein is important for growth and development. It is a part of every body cell. The body needs a constant supply of protein to repair body cells as they wear out. Protein is important to the organs, muscles, nervous system, blood vessels and skeleton. Children and adolescents require protein for normal growth and development. Proteins are also part of enzymes, such as antibodies that help protect from diseases and viruses. Protein also provides the body with an energy source. The body will use protein for energy if there is not enough carbohydrate and fat present. Otherwise it will be used for its other unique features.
The amount of protein needed by healthy people is small. The amount of protein an individual needs is dependent on their body weight. Extra protein in the diet is broken down and either leaves the body in urine or feces (stool) or is converted to other forms of energy.
Meats have about 7 grams of protein per 1 ounce serving. Examples include:
- 1 ounce of chicken, fish, turkey or beef
- 1 egg
- 1 ounce of cheese or 1/4 cup of cottage cheese
Dairy foods have about 8 grams of protein per serving. Examples include an 8-ounce serving of any of the following: skim, 2%, or whole milk, buttermilk or yogurt.
Some plant foods are high in protein. These include:
- nuts and seeds
- beans such as soy, pinto, black, kidney
- peanuts and other nuts.
A 1/2-cup serving of cooked dry beans provides about 7 grams of protein. Most adults need 2 to 3 servings every day of milk and 2 to 3 servings of lean meat or meat substitute. A serving can be 2 to 3 ounces.
Protein needs are relatively low; roughly 15% to 20% of the day's calories. It is easy to get enough protein from most diets. Even vegetarians can get enough protein, especially if they plan carefully. In fact, most Americans eat too much protein. Healthy adolescents and adults need about 0.8 grams of protein per kilogram of body weight, with the exception of 0.9 grams per kilogram for boys 15 to 18 years old. Infants and growing children need slightly more.
It is easy to figure out how much protein a person needs. Divide body weight by 2.2, this will give weight in kilograms (kg). Multiply this number by 0.8. Here is an example for a 120-pound person: (120 / 2.2) = 54.5 kg x 0.8 = 43.6 kg. This person needs about 44 grams of protein per day.
Too much protein may be harmful to the kidneys. The kidneys filter the by-products that come from the breakdown of protein. These by-products can be toxic to the body. Eating a very high protein diet puts stress on the kidneys because they have to work much harder. Also since complete protein comes from mostly animal products, diets high in protein are also high in fat, cholesterol and saturated fat. Too little protein in the diet generally is not a concern in the United States. However, it is still a problem in many parts of the world, where it results in malnutrition.
Duyff, R., MS, RD, CFCS. (1996). The American Dietetic Association's Complete Food&Nutrition Guide. Minnesota: Chronimed Publishing.