The main food sources of carbohydrates are: sucrose, grains (such as rice, wheat, corn, barley, oats, sorghum, etc. ), fruits (such as sugar cane, melon, watermelon, banana, grape, etc. ), nuts, vegetables (such as carrots, sweet potatoes and so on. ) and so on.

Carbohydrate 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.