There are two types of simple sugars: the monosaccharides and the disaccharides. These sugar molecules, identified by the number of carbon atoms, are the building blocks for more complex carbohydrates. Simple sugars are in every living organism, playing a role in processes ranging from energy storage to the structure of your DNA.
Glucose
Glucose is the most common monosaccharide in nature. Glucose circulates in your blood to supply immediate energy to your cells through a process called glycolysis. In glycolysis, a molecule of glucose is broken down to produce energy in the form of adenosine triphosphate, or ATP. Your body precisely regulates the level of glucose for optimal health. Glucose is stored for later use by your liver and regulated by the hormones insulin and glucagon. If this process does not work properly, levels of glucose in the blood can increase, resulting in diabetes. Diabetics test for glucose when they measure blood sugar levels.
Fructose and Galactose
Both fructose and galactose are monosaccharides. Fructose, found in both fruits and vegetables, is the sweetest tasting sugar. Honey gets its sweet taste from the high percentage of fructose. Corn syrup is 50 percent fructose, and makes a good sweetener for soft drinks, desserts and jams. Galactose is a simple sugar found in small amounts in food and results from the breakdown of more complex sugars in the diet. Galactosemia is a rare inherited disease that affects a patient's ability to digest galactose. The galactose sugar builds up in their body, damaging the liver, brain, kidneys and eyes. Patients with galactosemia must avoid milk and milk products as well as foods containing galactose such as beans and peas.
Other Monosaccharides
Simple sugars molecules with five carbon atoms are called pentoses. The pentose sugars, ribose and deoxyribose, are in the genetic material of every cell. RNA, or ribonucleic acid, contains ribose. The simple sugar, deoxyribose is part of your DNA, or deoxyribonucleic acid. Small quantities of sugar alcohols are in fruit, although prepared foods use large amounts of synthetically produced sugar alcohols. These simple sugars have a very sweet taste, but your body does not completely absorb them. Since sugar alcohols are not absorbed, they do not raise your blood sugar levels and so are useful as low-calorie sweeteners. Low-calorie desserts and chewing gum use the sugar alcohols, sorbitol and xylitol as sweeteners.
Disaccharides
Disaccharides are simple sugars made from two monosaccharides. The most familiar disaccharide is table sugar, or sucrose. This simple sugar is made of the monosaccharides glucose and fructose. Beets and sugar cane contain large amounts of sucrose. The disaccharide, lactose is in mammalian milk and consists of the simple sugars, galactose and glucose. Germinating grain, such as barley, contains the disaccharide maltose, which consists of two molecules of glucose. Also known as malt sugar, maltose is important in the brewing of beer.
References
- "Biochemistry Demystified"; Sharon Walker and David McMahon; 2008
- "Nutrition"; Paul Insel; 2010
- University of Maryland Medical Center; Galactosemia; April 15, 2009
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