Types of Food Protein
Protein is part of every cell in the human body. It's also an important part of the body chemistry, playing essential roles in replication of DNA and, on a larger scale, regulation of hormones. All proteins are made of chains of molecules called amino acids. There are 22 standard amino acids, of which eight are considered essential because they are not manufactured by the body in sufficient quantities and must be obtained through diet.
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Essential Amino Acids
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Isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine are the eight essential amino acids. Unlike the other 14 standard amino acids, the body cannot create enough of these compounds to meet its needs. In children, cysteine, taurine, tyrosine, histidine and arginine are semiessential because the metabolic pathways that create these molecules are not fully developed. Because it is not simply the amount of protein, but the type of protein consumed, eating a variety of protein-rich foods is crucial.
Complete Protein
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When thinking about types of food protein, the most important classification is drawn between sources of complete proteins versus incomplete proteins. A complete protein is a source for all eight essential amino acids. Most animal-based foods contain a complete protein. Meat, fish, milk, eggs and cheese, for example, all contain a complete protein. Quinoa is a rare example of a vegetable source of complete protein.
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Incomplete Protein
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Most vegetable sources of protein are incomplete. This means they're lacking in one or more of the essential amino acids. This situation is easily remedied, however, by combining incomplete protein sources to create a complete protein. Common food pairings that create a complete protein are rice and beans or peanut butter and bread. It was once thought you had to eat complementary proteins at the same time, but it is accepted now that incomplete proteins consumed in the same day can be combined by the body.
Quantity
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The U.S. Department of Agriculture recommended daily intake of protein is 0.4 grams per pound of ideal bodyweight. For most people, this breaks down to about 40 to 100 grams of protein per day, which should also be about 10 to 20 percent of total daily calories. Prolonged overconsumption of protein can caused damage to the liver and kidneys.
Food Source of Protein
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Though animal-based foods are rich in complete proteins, moderation is recommended with these foods. For one, they are usually high in saturated fats, which present a health risk if eaten too frequently. They are also nitrogen-rich, and therefore more likely to cause kidney and liver damage. Vegetable sources, especially legumes, have nearly as much protein as red meat, especially when combined with complementary proteins, with few or none of the health risks.
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