D-Psicose (D-allulose, D-ribo-2-hexulose, C6H12O6) is an ultralow-energy monosaccharidesugar. It is a C-3 epimer of D-fructose, and is present in small quantities in agricultural products and commercially prepared carbohydrate complexes. It is known as a "rare sugar" because it is rarely found in nature, and even when found, only in small amounts. D-Psicose yields only 0.3% the metabolic energy of the equivalent amount of sucrose. Its name derives from the antibioticpsicofuranine, from which it can be isolated. Research is being conducted into how it can be used in diets to aid in combating hyperglycemia, hyperlipidemia, and obesity. The first mass production method for D-psicose was established when Ken Izumori at Kagawa University in Japan discovered the key enzyme, D-tagatose 3-epimerase, to convert fructose to D-psicose in 1994. This method of D-psicose production, called Izumoring named after Izumori, has a high yield but suffers from a very high production cost. In 2012, Food and Drug Administration (FDA) approved D-psicose as a food additive and designated it as generally recognized as safe (GRAS).