There are two types of carbohydrates, also known as sugars: monosaccharides (represented by glucose and fructose), disaccharides (represented by sucrose) and polysaccharides (represented by starch), which can be digested and absorbed to produce heat. The other type is cellulose (also polysaccharide), which cannot be digested and absorbed, and does not produce heat. Compared to proteins and fats, carbohydrates are digested and absorbed faster and more completely than proteins and fats. Carbohydrates are digested by the body into monosaccharides (mainly glucose) and then absorbed. After absorption a portion of the glucose remains in the blood. The fasting glucose level within the blood of a normal person is 4-6.1 mmol/L. The blood glucose level 2 hours after a meal is less than 7.8 mmol/L. A portion is stored as glycogen in the liver and muscle. The released glycogen is converted into glucose to provide calories for the body at any time as needed. The conversion of glucose to glycogen and calories must involve insulin. Some of the glucose can also be converted to fat for storage. When there is a lack of insulin in the body or a decrease in insulin activity (when the insulin level in the blood is normal or even increased, but cannot function normally, it is called insulin resistance), then glucose metabolism becomes impaired and blood glucose increases, which is called diabetes. Carbohydrates are found in all foods. Glucose contains 100% carbohydrates. Sucrose, starchy rice, flour, grains and cereals contain about 80-60%. Legumes contain 30-50%. Potatoes, yams, taro, sweet potatoes and other root foods contain about 15-25%. Pumpkin and other squash, milk, vegetables contain about 2%-5%. Fruits contain 5%-20%. Carbohydrates are the main source of calories for the body. The alcohol transformed from carbohydrates is ethanol, and one gram of alcohol can produce up to 7 kilocalories.