Carbohydrates are one of the basic types of nutrients. Their primary function is to provide energy for the body.
AdvertisementsThe term carbohydrate, literally means "hydrates of carbon" as most of the forms of carbohydrates have the empirical formula CH2O. More accurately, carbohydrates are now defined as polyhydroxy aldehydes and ketones. They are classified as simple or complex carbohydrates, depending on the type of their chemical structure.
In food science and biochemistry, the term carbohydrate is used synonymously for saccharide, a group that includes sugars, starch and cellulose. The origin of the word saccharide is from the Greek word σάκχαρον (sákkharon), meaning 'sugar.' Depending upon the chemical structure, the saccharides are divided into monosaccharides, disaccharides, oligosaccharides and polysaccharides. The term 'sugars' is used synonymously for saccharides, particularly for monosaccharides and disaccharides.
Most types of compounds with formula Cm (H2O) n are termed carbohydrates. In biochemistry, those compounds with one (formaldehyde 0r CH2O) or two (glycolaldehyde or C2H4O2) carbon atoms are excluded.
Some nutritionists use the term complex carbohydrate to refer to digestible and indigestible saccharide present in unprocessed whole food, as opposed to that present in processed and refined type of food products, table sugar and refined glucose.
Simple carbohydratesSimple carbohydrates have one or two sugar units. They occur in fruits, milk products, certain vegetables, table sugar, honey, candy, syrups, carbonated beverages, cane juice and beet. Monosaccharides and disaccharides are the two types of simple saccharides. The food having high levels of simple type of carbohydrates may be deficient in fiber, minerals and vitamins.
MonosaccharidesThe common monosaccharide type of carbohydrates are glucose, fructose, and galactose. Monosaccharides have single sugar unit. Of these, glucose is the main saccharide metabolized by the body to produce energy. Other types of monosaccharides after being absorbed from the intestine, have to be converted into glucose in the liver for utilization.
Galactose is present in the nature in small quantities and it combines with glucose in the milk to create lactose, milk sugar. Fructose has the same chemical formula but a completely different type structure. Fructose is present in fruits, honey and high-fructose corn syrup.
DisaccharidesDisaccharide type of carbohydrates have two sugar units. The common examples are, sucrose, lactose and maltose. The condensation of two monosaccharides and release of one water molecule creates a disaccharide. Sucrose is the common table sugar has molecules of glucose and fructose. Sucrose is the sweetest of all the disaccharides. It is extracted from sugar cane or sugar beet.
Maltose or malt sugar contains two glucose molecules. It is an important component of barley malt used in breweries. The condensation of glucose and galactose creates lactose molecule. Lactose, or milk sugar is digested by the enzyme lactase. Some people lose this ability to digest lactose and develop lactose intolerance.
Complex carbohydratesComplex type of carbohydrates have more than two sugar units. They occur in whole-grains, cereals and in vegetables such as beans, peas, potatoes, corn, green peas, lentils and peanuts. Oligosaccharides and polysaccharides are the two types of complex saccharides. The food having high levels of complex saccharides may also contain dietary fiber, vitamins and minerals.
OligosaccharidesOligosaccharide type of carbohydrates often have a chain of three to ten monosaccharide units. Several fruits and vegetables contain fructo-oligosaccharides bonded by short chains of fructose molecules. Dietary fibers are galacto-oligosaccharides present in several natural foods. Apart from functioning as prebiotics, these types of carbohydrates are helpful in stimulating the activity of beneficial bacteria in the colon and also provide bulkage for stimulating peristalsis.
PolysaccharidesIn nature most of the carbohydrates exist as polysaccharides. These types of carbohydrates have long chain (more than ten) of monosaccharide units. They may have linear or highly branched structure. Starch, glycogen, cellulose and chitin are some of the types of polysaccharides. Intestinal amylases enzymes break down starch into monosaccharide units for absorption. Starch is present in potatoes, beans, cereals and grains. Glycogen is an energy reserve and is primarily made by the liver and the muscles.
Cellulose is the most abundant carbohydrate in nature and is the most abundant of all biological molecules. Cellulose is the main component of the plant cells. There are no side chains in cellulose and the linear molecules lie close together. Human beings lack enzymes to digest cellulose. Chitin and pectins are the other natural polysaccharides, being indigestible, have no direct value in human food. The bacteria present in the colon can digest these fibers and an energy value of 2kcal/g (8.4kJ) may be contributed by these carbohydrates.
Some of the dietary fibers are arabinoxylans, cellulose, inulin, lignin, waxes, chitins, pectins, beta-glucans and oligosaccharides. These carbohydrates function as prebiotics and also provide bulkage for stimulating peristalsis. They are particularly helpful in lowering the glycemic index of the ingested food. Dietary fibers slowing down the digestion and absorption of carbohydrates in the intestines.
2.Kiens B, Richter EA. Types of carbohydrate in an ordinary diet affect insulin action and muscle substrates in humans. Am J Clin Nutr. 1996 Jan;63(1):47-53.