Common, refined, white granulated sugar is a nearly pure carbohydrate* that occurs naturally in every fruit and vegetable in the plant kingdom. It is a major product of photosynthesis, the process by which plants convert solar energy and atmospheric carbon dioxide into stored food energy, and oxygen. Sugar occurs in greatest quantities in sugar cane and sugar beets.
Chemically sugar is the disaccharide "sucrose" that results from the biochemical bonding of the naturally-occurring monosaccharide molecules "fructose" (also called "levulose" or "fruit sugar") and dextrose (also called "glucose" or "grape sugar"). This bond is relatively strong, but it is commonly broken by heat, acids, and the enzyme "invertase," present in human saliva and digestive tracts. The process of splitting sucrose into its two components —fructose and dextrose — is alternatively called "inversion" and "hydrolysis."
Sugar is a carbohydrate, a substance composed of only carbon ("carb-"), oxygen ("-o-"), and hydrogen ("-hydrate."). Sucrose, fructose, dextrose, lactose (milk sugar) and other " -oses" are members of this chemical class. When tens or hundreds of thousands of dextrose monosaccharides are chemically linked (polymerized), the resulting compounds are starch and cellulose.
All carbohydrates — sucrose, fructose, glucose, starch and so-called "complex carbohydrates"— contain the same caloric content: about 4 calories per gram. Neither nature nor human biochemical pathways distinguish calorically between refined table sugar and the sucrose in, say, an orange. The sucrose present in a bowl of table sugar is identical, chemically and metabolically, to the sucrose found in fruits and vegetables.