The common sugars that form part of the diet are sucrose, lactose (milk sugar), and maltose. They are all disaccharides and are split into monosaccharides during digestion; sucrose to glucose and fructose, lactose to galactose and glucose, and maltose into two glucose molecules. All three monosaccharides — glucose, galactose and fructose — can be metabolized by the body and used as a source of energy, although glucose is by far the most important, and is normally maintained within a narrow range of concentration in the blood. Fructose is also a dietary component in fruit. Some people congenitally lack lactase, the enzyme which splits the lactose molecule in the intestine, and consequently suffer abdominal discomfort and diarrhoea after ingesting lactose. Lactose is present in milk and while few Europeans suffer lactase deficiency, some 97% of Thais, for example, are without this enzyme; in most instances this is likely to be the consequence rather than the cause of the rarity of milk-drinking and cheese-eating in this and Eastern communities, since their infants have no problem. Starch (a polyglucose) is broken down during digestion into maltose and then into glucose.
Sugars have multiple functions within the body and are used as a primary source of energy, through the synthesis of ATP, and for energy storage. When the body stores glucose it does so as glycogen (body starch). Glycogen stores in muscle provide readily available glucose for exercise; glycogen stores in the liver are crucially involved in the maintenance of blood sugar — the concentration of glucose in the blood. This in turn is vital as a nutrient supply to the brain, which normally utilizes only glucose for energy production.
Five-carbon sugars (pentoses) also have a crucial significance in the body. For example, ribose and deoxyribose are essential for the formation of the backbone of RNA and DNA. As well as forming part of the molecules determining inheritance and phenotype, sugars are linked to proteins and lipids, to form glycoproteins and glycolipids. Glycoproteins include antibodies and clotting factors. Other proteins and lipids expressed in the membranes of cells and linked to sugars are responsible for cell-to-cell recognition and adhesion, and are involved in the processing of messages brought by hormones and neurotransmitters and, in cells in the spleen and elsewhere, in recognizing old circulating red cells and removing them.
Alan W. Cuthbert
See also blood sugar; carbohydrates; insulin; metabolism.
"sugars." The Oxford Companion to the Body. . Encyclopedia.com. (May 17, 2019). https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/sugars
"sugars." The Oxford Companion to the Body. . Retrieved May 17, 2019 from Encyclopedia.com: https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/sugars
Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).
Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.
Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:
Modern Language Association
The Chicago Manual of Style
American Psychological Association
- Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
- In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.