Carbohydrates are organic molecules that range in size from small molecules such as the blood sugar glucose, which cells use to generate energy, to very large ones such as starch.
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. Carbohydrates’’ primary function is to supply energy for cellular work, 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.
People also ingest lots of carbohydrate in beverages like soft drinks, much to the chagrin of nutritionists, as these drinks provide lots of calories but few, if any other essential nutrients.
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.
In the digestive system, starch is broken down into glucose molecule. Glucose then enters the blood stream, Here it circulates throughout the body, providing a source of energy for the cells.
Lactose is a naturally occurring carbohydrate found in the milk of mammals. It serves as the principle of carbohydrate and energy for their young. It is much less sweet than sucrose and has a relatively bland taste.
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.
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.
Dietary intake of plant materials is the major carbohydrate source for humans. The average human diet should ideally be about two-thirds carbohydrate by mass.
Carbohydrates in human body
