Food refers to food containing carbohydrates, which is one of the essential nutrients for human body. Most carbohydrates naturally exist in plant foods, such as cereals. People usually think that carbohydrates are only rice, noodles, bread, noodles, potatoes, sweets, sugary drinks and so on. In fact, carbohydrate foods also include all cereals such as sweet potatoes, corn and peas, as well as yogurt, milk, fruits, vegetables, nuts and various beans. Sugar is the simplest form of carbohydrate and exists in natural foods, such as fruits, vegetables, milk and dairy products. The main types of sugar are fructose, sucrose and lactose. Starch is a complex carbohydrate, which is composed of simple glycogen. Starch naturally exists in vegetables, grains and some beans. Dietary fiber is also a complex carbohydrate, which naturally exists in fruits, vegetables, whole grains and some beans. Generally speaking, high-fiber carbohydrates include beans, whole grains, starch, vegetables and fruits. High-protein carbohydrates include beans, yogurt, milk and so on. And low-fiber carbohydrates include refined grains, sweets, sugary drinks and so on.