Carbohydrates an important category of substances in food, include all sugars, starch, cellulose, hemicelluloses, pectin, and the various sorts of gum. They make up most of the solid matter in plants. Animals, however, whose solid matter consists mostly of proteins, contain only a little carbohydrate (apart from any undigested food they may have on board).
Plants store energy in the form of carbohydrates. When people and animals eat the plants they release this energy and can use it for their own purposes. Carbohydrates are the main source of energy for most peoples of the world. In an average western diet, for example, 55 to 65 per cent of the energy comes from carbohydrates, the rest from fats and proteins. In a typical Japanese diet the figure for carbohydrates is about 80 per cent.