Carbohydrate definition and food sources

With the energy value of 4 calories, carbohydrates are one of the most basic nutrients in foods. They are indispensible in foods by virtues of their role as sweeteners, thickening, bulking and gelling agents.

Carbohydrates are composed of three elements: carbon, hydrogen and oxygen. The word carbohydrate was originally derived from the fact that the greater part of the compound in this class had the empirical formula Cn(H2O)n. The values of n range from three to many thousands. The number and arrangement of these elements in the carbohydrate molecule differentiate one carbohydrate from another.

This formula now considered too restrictive and a more useful definition might be ‘polyhydroxy aldehydes or ketones and their derivatives’. This later definitions encompass deoxy sugars, sugar alcohols, sugar acids, amino sugars.

Plants are the primary sources of carbohydrates in the human diet. Carbohydrates occur in fruits and vegetables as storage reserves in seeds, roots, and tubers; in the sap; and as constituents of the structural tissues, they are also found in the milk, blood, and tissues of animals.

Carbohydrate should make up about 5/7 of the solid part of the diet and ideally no more than 2/7 of the carbohydrates should be refined sugars such as glucose.
Carbohydrate definition and food sources 

Carbohydrates

Carbohydrates
Unlike proteins, the carbohydrates in the body contribute nothing to the structure of tissue and although they contribute to the regulation of metabolism, they do not control individual molecular events as the enzymes (proteins) do. Their major function is the provision of energy to a variety of tissues, especially to the brain and nervous system which cannot utilize other nutrients for energy.

The carbohydrates in a typical breakfast – toast and tea with milk and sugar – are roughly representative of the distribution of carbohydrate in the average diet: starch from bread, potatoes, rice, pasta: sucrose from sugar: and lactose from milk. Starch is large molecule made up of many glucose units joined together, all glucose units being of similar structure. It is rapidly digested to its basic glucose units which are readily absorbed.

Lactose and sucrose are by contrast very much small molecules, each of which is digested to become effectively (in the liver) two units. The enzymes responsible for their digestion are, respectively, lactase and sucrase. There is rarely a problem is the digestion of sucrose but a great number of number people encounter problems with lactose digestion, most of which are associated with and inadequate supply of lactase.

Undigested lactose passes from small intestine, where digestion and absorption of its glucose units should occur, into the large intestine, where bacteria (a normal non pathogenic population of microbes) ferment the lactose and cause digestive upsets and diarrhea. The bulk of the population of Africa, Southern Europe, and the near East develop lactose intolerance during later childhood and adult life.

Under normal conditions, however the great majority of carbohydrates in our typical meal are digested and absorbed as glucose, if you measured blood glucose levels before such a meal and at half hourly intervals thereafter, you would see a rise in blood glucose, peaking at about the half hour mark and returning to fasting levels almost as quickly. If you were to abstain from carbohydrates for a considerable period say a week, your blood glucose levels would still be normal in spite of a minimal or zero intake, the body’s capacity to maintain blood glucose within specific limits is achieved by a variety of hormones, the two most important of which are insulin and glucagon. Both are secreted by the pancreas into bloodstream, as required.
Carbohydrates