In the United States, six high-intensity sugar substitutes have been approved for use: aspartame, sucralose, neotame, acesulfame potassium (Ace-K), saccharin, and advantame. Food additives must be approved by the FDA, and sweeteners must be proven as safe via submission by a manufacturer of a GRAS document. The conclusions about GRAS are based on a detailed review of a large body of information, including rigorous toxicological and clinical studies. GRAS notices exist for two plant-based, high-intensity sweeteners: steviol glycosides obtained from stevia leaves ("Stevia rebaudiana") and extracts from "Siraitia grosvenorii", also called "luo han guo" or monk fruit.