Carbohydrates (sugars) are the main life-sustaining nutrients for the human body. Monosaccharides such as glucose, fructose and galactose; disaccharides such as sucrose (brown sugar, white sugar), maltose and lactose; and polysaccharides such as starch, dextrin and glycogen are all carbohydrates. Disaccharides and polysaccharides need to be broken down by digestive enzymes into monosaccharides before they can be absorbed and used by the body. The sugar required by human is mainly taken from the starch of food, which is finally turned into monosaccharide, i.e. glucose, through a series of decomposition steps before it is absorbed by the intestine as an important source of caloric energy. Carbohydrates have a variety of physiological energy supply: (1) supply the body needs heat energy, about 70% of the body’s heat energy provided by carbohydrates. Each gram of sugar in the body produces 4.1 kilocalories (17.16 kilojoules) to maintain the body’s metabolism, and is the only source of heat available to the nervous system; (2) fat metabolism, must rely on carbohydrates to supply heat to complete the fat oxidation process. When carbohydrates are insufficient, incomplete oxidation of fats produces ketosis, which is often seen when acidosis occurs in diabetes, and adequate carbohydrates can prevent acidosis in diabetes; (3) excess glucose produced in metabolism can be converted into glycogen, which is mainly stored in the liver and muscles. The body can break down glycogen into glucose for the body’s metabolic needs when there is a shortage of sugar in the body. The abundant liver glycogen can protect the detoxification function of the liver. As the elderly age, their tolerance to sugar metabolism decreases. Carbohydrates for the elderly should be mainly cereals, with minimal sweet snacks, foods and beverages. Carbohydrates for the elderly should account for 50% to 55% of total calories, and generally not more than 60%.