Fat substitutes are the substances most similar to fats functionally. They are heat stable, which is not true of all fat replacers. These substances generally contribute fewer calories than regular fats (or no calories at all) because of their molecular structure and/or because of the way the body handles them. One example of a fat substitute is olestra. Olestra is composed of the sugar sucrose (table sugar) and from six to eight fatty acids. Because of the way in which the fatty acids are attached to the sucrose, humans are unable to digest and absorb olestra; thus, it contributes no calories.