"Simple carbohydrates are also known as sugars and are grouped as either monosaccharides or disaccharides. Monosaccharides include glucose, fructose, and galactose, while disaccharides include lactose, maltose, and sucrose. Simple carbohydrates stimulate the sweetness taste sensation, and sweetness varies among the different carbohydrate types. Fructose is the top naturally occurring sugar in sweetness value. For all organisms from bacteria to plants to animals, glucose is the preferred fuel source. The brain is completely dependent on glucose as its energy source except during extreme starvation conditions. Galactose differs from glucose only in the direction of a hydroxyl group on the number four carbon. The liver rapidly converts galactose to glucose, and most absorbed galactose is used for energy production after this conversion. Fructose has the same chemical formula as glucose but differs in its chemical structure because its ring contains five carbons rather than six. It is mostly found in fruits, honey, and sugarcane, and is also found in soft drinks, cereals, and other products sweetened with high fructose corn syrup. Pentoses are less common monosaccharides with five carbons; they are abundant in RNA and DNA and are also components of fiber. Sugar alcohols, such as sorbitol, xylitol, and glycerol, are industrially synthesized derivatives of monosaccharides. They are often used in place of table sugar because they are incompletely digested and absorbed and therefore provide fewer calories. Sugar alcohols do not cause tooth decay, and their dissolving in the mouth can produce a sensation of coolness."