Definition 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.
Protein provides 17 kilojoules per gram. It is chemically unique from fat and carbohydrate because it contains nitrogen.
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 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:
beef
lamb
pork
poultry
fish
shellfish
eggs
dairy products
Vegetable foods that are high in protein include all kinds of legumes such as peas, beans, grains and some vegetables. Soy is often considered the most "complete" plant protein source.
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 used to form enzymes, and other essential components 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.
Information 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 faeces (stool) or is converted to other forms of energy.
The best sources of "complete" protein come from the middle, the lean meats and milk section of the Australian Guide To Healthy Eating. Foods from the meat group have about 10 grams of protein per 50 gram serving. Examples include:
50 grams of chicken, fish, beef, lamb or pork = 10-11g
1 large egg = 8g
Dairy foods have about 8 grams of protein per serving. Examples include a 250 ml serving of any of the following: skim, reduced fat, or whole milk, buttermilk or 200g tub of yoghurt.
Some plant foods are high in protein. These include:
legumes
nuts and seeds
beans such as soy, baked beans, three bean mix, kidney
peas
peanuts and other nuts.
A 1/2-cup serving of cooked dry beans provides about 5 grams of protein. Most adults need 2 to 4 servings every day of milk and 1 to 2 servings of lean meat or meat substitute. A serving can be 65-100g lean meat or 1/2 cup cooked (dried) beans.
Protein needs are relatively low; roughly 15% to 20% of the day's kilojoules. It is easy to get enough protein from most diets. Even vegetarians can get enough protein, especially if they plan carefully. In fact, most Australians eat too much protein. Healthy adults need about 0.75 grams of protein per kilogram of body weight. Infants and growing children need slightly more, 1-1.2 grams per kilogram of weight.
It is easy to figure out how much protein a person needs. Multiply your own weight in kilograms (kg) by 0.75. Here is an example for a 55 kg person: 55kg x 0.75 = 45 grams. This person needs about 45 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 may also be high in fat, cholesterol and saturated fat. Too little protein in the diet generally is not a concern in Australia. However, it is still a problem in many parts of the world, where it results in malnutrition.
Author: Clare Armstrong, MS, RD Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
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