Fructose, C6H12O6, is a simple ketonic monosaccharide which, when placed in solution, forms a five or six-member ring containing one oxygen atom. The five-member form, fructofuranose, is less sweet than the six-member form, fructopyranose. Fructofuranose is the isomer found in the common sweetener sucrose. While the metabolism of fructose is not fully understood, its frequent use as a sweetener has given it a negative reputation because excessive consumption can eventually cause metabolic syndrome. The reason for its use in food is because fructose is inexpensively sourced from plants and honey, is the sweetest naturally occurring carbohydrate, retains its flavor at low temperatures and is the most water-soluble sugar. Plants such as fruits, tubers and corn need fructose because it causes freezing point depression which protects them from ice crystallization. This relevance of fructose to both humans and nature makes it an important molecule.