Also called fruit sugar and levulose, this extremely sweet substance is a natural by-product of fruits and honey. It's more water-soluble than glucose and sweeter than sucrose (though it contains half the calories). Unlike glucose, it can be used by diabetics. Fructose comes in granulated and syrup forms. Except in the case of some liquids, such as a sauce or beverage, it should not be substituted for regular sugar (sucrose) unless a recipe gives specific substitution. When heated, fructose loses some of its sweetening power.