Threitol is a four carbon sugar primarily used in the chemical synthesis of other compounds. It is a diastereomer of erythritol an FDA approved low-calorie sweetener. Threitol can be found in meaningful concentrations in the edible fungus Armillaria mellea and is used by some organisms as an antifreeze agent, such as the Alaskan beetle. Threitol is a very weak inhibitor of Carbonic anhydrase. Threitol is the main end product of D-xylose metabolism in humans and deficiency is associated with inborn errors of metabolism.