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Carbohydrates are the most common source of energy for the human body. Protein builds tissue and cells in the body. Carbohydrates are very good for energy, but, if a person eats more than needed, the extra is changed into fat. If necessary, humans can live without eating carbohydrates because the human body can change proteins into carbohydrates. People of some cultures eat food with very little carbohydrates, but they still remain healthy.

Carbohydrates are found in a wide variety of foods. The important sources are cereals (wheat, maize, rice), potatoes, sugarcane, fruits, table sugar (sucrose), bread, milk, etc. Starch and sugar are the important carbohydrates in our diet. Starch is abundant in potatoes, maize, rice and other cereals. Sugar appears in our diet mainly as sucrose (table sugar) which is added to drinks and many prepared foods such as jam, biscuits and cakes. Glucose and fructose are found naturally in many fruits and some vegetables. Glycogen is carbohydrate found in the liver and muscles (as animal source). Cellulose in the cell wall of all plant tissue is a carbohydrate. It is important in our diet as fibre which helps to maintain a healthy digestive system.

Research in the United States and Canada have shown that people get about 40% to 60% of their energy from carbohydrates. However, studies suggest that some people get at least 55% to 75% of energy from carbohydrates. It may depend on the amount of physical work done by people: the harder the work, the more energy they need. The other need for energy is body temperature. Living in a cold climate means a person needs more energy.