Carbohydrate consists of three elements: carbon, hydrogen and oxygen. Because the ratio of hydrogen to oxygen is two to one, which is the same as water, 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. The general chemical formula of carbohydrate is C6H 12O6.

Carbohydrate is the main source of energy needed by all living things to maintain life activities. It is not only a nutrient, but also some of them have special physiological activities. For example, heparin in the liver has anticoagulant effect; The sugar in blood type is related to immune activity. In addition, the components of nucleic acid also contain carbohydrates-ribose and deoxyribose. Therefore, sugar compounds are more important to medicine.