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A balanced diet is one that provides an adequate intake of energy and nutrients for maintenance of the body and therefore good health. A diet can easily be adequate for normal bodily functioning, yet may not be a balanced diet. Carbohydrates Carbohydrates are a rapid source of energy, they are the bodys fuel. The bulk of a balanced diet should be made from carbohydrates. If eaten in an excess of the dietary requirements carbohydrates are easily stored as fats in the cells, although carbohydrate is the first source of energy in the body. An average adult requires about 12,000kJ of energy a day, most of this is supplied by the respiration of carbohydrates in the cells. Carbohydrates are used principally as a respiratory substrates, i.e. to be oxidised to release energy for active transport, macromolecule synthesis, cell division and muscle contraction. Carbohydrates are digested in the duodenum and ileum and absorbed as glucose into cells. Sources of carbohydrates such as starch are rice, potatoes, wheat and other cereals. Sugars are also carbohydrates, sources of sugars are refined sugar - sucrose, which is a food sweetener and preservative and fruit sugars - fructose. If the diet lacks carbohydrate stores of fat are mobilised and used as an energy source. Proteins Protein is not a direct source of energy in the body, it is used primarily for growth and repair of body tissues while remaining an energy source as a last resort. Proteins fulfill a wide variety of roles in the body. They are broken down in the stomach and intestines to amino acids which are then absorbed. The body can only form 8 amino acids to build proteins from, the diet must provide Essential Amino Acids which are synthesised into proteins which can be structural, i.e. collagen in bone, keratin in hair, myosin and actin in muscle; metabolic enzymes, hemoglobin, protective antibodies and communicative hormones. | 
