Carbohydrates are composed of three elements: carbon, hydrogen, and oxygen. Because the ratio of hydrogen and oxygen it contains is two to one, the same as water, it is called carbohydrates. It is the cheapest of the three main nutrients that provide heat energy to the human body. Carbohydrates in food are divided into two categories: effective carbohydrates that humans can absorb and utilize, such as monosaccharides, disaccharides, and polysaccharides, and ineffective carbohydrates that humans cannot digest, such as cellulose, which are essential substances for the human body. The general chemical expression of carbohydrates is C6H12O6.

Carbohydrates are the main source of energy required by all living organisms to maintain life activities. It is not only a nutrient, but some also have special physiological activities. For example: heparin in the liver has an anticoagulant effect; sugar in the blood group is related to immune activity. In addition, nucleic acids also contain sugar compounds - ribose and deoxyribose. Therefore, carbohydrate compounds are of greater significance to medicine.