Acesulfame Potassium, or acesulfame-K has a structure that's similar to saccharin. The letter K stands for potassium. It's not toxic and is not a source of dietary potassium -- after it's absorbed, almost all the acesulfame-K molecules remain unchanged and are excreted in the urine.
Acesulfame-K is heat-stable so it can be used for cooking. It's been approved for general use in foods and is found in many food products worldwide.
Sucralose and aspartame are more popular in US, but acesulfame-K is found worldwide. Sunett and Sweet One are two brands. It's about 150 to 200 times sweeter than sugar, so very little is needed to sweeten foods. Acesulfame-K adds no calories to foods.
It' has been blamed for causing tumors in rats. However, the overwhelming majority of studies show it to be safe. In fact, acesulfame-K has been shown to be safe in more than 90 studies by the FDA and the Food and Agriculture Organization/World Health Organization (FAO/WHO) Joint Expert Committee on Food Additives.
The Academy of Nutrition and Dietetics considers acesulfame-K safe when used as part of a healthy eating plan.
Other No-Calorie Sweeteners
Academy of Nutrition and Dietetics. "Position of the Academy of Nutrition and Dietetics: appropriate use of nutritive and non-nutritive sweeteners." J Am Diet Assoc. 2004 Feb;104(2):255-275.
United States Food and Drug Administration. "Artificial Sweeteners: No Calories ... Sweet!" July 2006.