There are many different kinds of sugars found in prepared and processed foods. All of these sugars contain about the same carbohydrates and deliver the same amount of calories, and so are essentially equivalent to white table sugar. However, simple sugars, at their most basic level, are distinguished by being either monosaccharides or disaccharides.
See also: How Is Sugar Made? What Kinds of Sugar Are There?
The Monosaccharides
Monosaccharides are the simplest form of carbohydrates. They cannot be reduced in size by hydrolysis and so are sometimes called “simple sugars”. However, in common usage, the term simple sugar usually also includes disaccharides, discussed below, which are two monosaccharides bonded together.
The three main monosaccharides important in human nutrition are glucose, fructose, and galactose. Glucose, a 6-carbon atom, is by far the most abundant monosaccharide in nature and the most important nutritionally.
Fructose is another monosaccharide found in fruits, flower nectar, honey, and the sap of trees. It is a good deal sweeter than glucose.
The third simple sugar is galactose, which is a component of “milk sugar”, a disaccharide called lactose. Glucose, fructose, and galactose are all classified as a triose, referring to the number of carbon atoms in their saccharide unit (tri- means “three” and -ose means “sugar).
Disaccharides
Disaccharides are the most abundant form of oligosaccharides, which consist of short chains of monosaccharide units joined by covalent bonds.
Sucrose, the disaccharide in white table sugar, is the most important nutritionally, comprising at least a third of the carbohydrate intake in an average diet. It is what most of us think of when we say the word “sugar.” Sucrose contains equal amounts of bonded glucose and fructose (ß-D-fructofuronasyl-α-D-glucopyranoside). Sucrose contains 5 grams of carbohydrate per teaspoon, delivering about 20 kilocalories.
Lactose is the principal carbohydrate of milk, composed of equal parts glucose and galactose. The third disaccharide is maltose.
Maltose, or “malt sugar” is two glucose units linked together. It is produced anytime starch breaks down. 1Brown, Amy C. Understanding Food: Principles and Preparation. Belmont, CA: Wadsworth Pub, 2011.,2Groff, James L., and Sareen Annora Stepnick. Gropper. Advanced Nutrition and Human Metabolism. Belmont, CA: Wadsworth/Thomson Learning, 2000.,3Webb, Frances Sizer., and Eleanor Noss. Whitney. Nutrition Concepts and Controversies. Australia: Wadsworth Thomson Learning, 2003.