Carbohydrate

Key points

• The two main types of carbohydrate are sugars and starch. Sugars and starch provide energy. 1 gram provides 16 kJ (3.75 kcal).
• Fibre is a type of carbohydrate found only in plants. Unlike other carbohydrates, it is not absorbed in the small intestine to provide energy, although some metabolism occurs in the large bowel. It is needed to keep the digestive system healthy.
• At least half the energy in our diets should come from carbohydrate, mostly as starchy carbohydrates.

Carbohydrate as a nutrient

Carbohydrate has many important functions as a nutrient:

• It provides energy. One gram of carbohydrate provides 16kJ (3.75kcal). For the purposes of food labeling, a conversion factor of 17kJ (4kcal) is used.
• The body’s tissues require a constant supply of glucose, which is used as a fuel. The main source of glucose is dietary carbohydrate but it can also be synthesised from protein. If the diet is low in carbohydrate, a greater percentage of dietary protein is used to provide glucose, which means less is available for the growth and repair of body tissues. Thus, carbohydrate in the diet has a protein-sparing effect.

Carbohydrates in the diet
National survey data for Great Britain found the average daily intake of carbohydrate was 275g for men and 203g for women. This represented 47.7% of food energy intake for men and 48.5% of food energy for women. Cereal and cereal products were the main source of carbohydrate for adults in Britain (including 21% of carbohydrate in the form of bread).

Further Information
Department of Health (1991) Dietary Reference Values, A Guide. HMSO, London.

Henderson L, Gregory J, Irvine & Swan G (2003) The National Diet and Nutrition Survey: adults aged 19 to 64 years. Energy, protein, carbohydrate, fat and alcohol intake. HMSO, London.

Holland B, Welch AA, Unwin ID, Buss DH, Paul AA, Southgate DAT (1991). McCance and Widdowson's The Composition of Foods, 6th edition. Royal Society of Chemistry, Cambridge.

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