The peanut, or Groundnut (Arachis hypogaea) is a species in the legume family Fabaceae native to South America, Mexico and Central America.
The plant's name combines the morphemes pea and nut, causing some confusion as to the nature of the fruit. Although a nut in the culinary sense, in the botanical sense the fruit of the peanut plant is a woody, indehiscent legume and not a nut. The word pea describes the edible seeds of many other legumes in the Fabaceae family, and in that sense, a peanut is a kind of pea.
Peanuts are a rich source of protein (roughly 30 grams per cup after roasting). Prior to 1990 the PER method of protein evaluation considered peanut protein along with soy protein an incomplete protein, containing relatively low amounts of the essential amino acids, cystine, and methionine (but high in lysine), and it was advised to be sure that a diet or meal with peanuts as a staple also include complementary foods such as whole grains like corn and wheat, which are adequate in methionine but limited by lysine. Protein combining has been largely discredited. Since 1990 the gold standard for measuring protein quality, is the Protein Digestibility Corrected Amino Acid Score (PDCAAS) and by this criterion peanut protein and other legume proteins such as soy protein is the nutritional equivalent of meat and eggs for human growth and health. An example of an extremely nutritious peanut-based food to restore health in starving-malnourished children is Plumpy'nut.
Although many people enjoy foods made with peanuts, some people have severe allergic reactions. For people with peanut allergy, exposure can cause fatal anaphylactic shock. For these individuals, eating a single peanut or just breathing the dust from peanuts can cause a fatal reaction. An allergic reaction also can be triggered by eating foods that have been processed with machines that have previously processed peanuts, making the avoidance of such foods difficult.
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