carbohydrate is composed of three elements: carbon, hydrogen and oxygen. Because the ratio of hydrogen to oxygen is two to one, it is the same as water, so it is called carbohydrate. It is the cheapest of the three main nutrients that provide heat energy for human body. Carbohydrates in food can be divided into two categories: effective carbohydrates that people can absorb and utilize, such as monosaccharides, disaccharides, polysaccharides and ineffective carbohydrates that people can't digest, such as cellulose, which are essential substances for human body.

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Before people knew the chemical properties and composition of carbohydrates, carbohydrates had played a very good role. Now, plants rich in carbohydrates are used as food, which are used to make fermented drinks and feed for animals. It was not until the 18th century that a German scholar separated pure sugar from beet and glucose from grape that carbohydrate research developed rapidly.

in p>1812, Russian chemists reported that the main form of carbohydrates in plants is starch, which can be hydrolyzed into glucose when heated in dilute acid. In 1884, another scientist pointed out that carbohydrates contain a certain proportion of three elements, C, H and O, in which the ratio of H to O is exactly the same as that of water, which is 2: 1, like a compound of carbon and water, so they are called carbohydrates.