Acesulfame-Potassium is the sweetener also known as E950, Acesulfame K, and Ace K, which is marketed as Sunnett and Sweet One. Chemists refer to is as the potassium salt of 6-methyl-1,2,3-oxathiazine-4(3H)-one 2,2-dioxide. Its most common name is Acesulfam K.
Like several other artificial sweeteners, Acesulfame K was discovered by accident. In 1967 a German chemist named Karl Clauss got dust from some chemicals with which he was working on his fingers. Neglecting to wash his hands, he licked a finger to pick up a piece of paper and noticed an unusually sweet taste. In the 45 years since the discovery of Acesulfame K, it has become the sweetener of choice for tart juice drinks.
You are most likely to encounter Acesulfame K in artificially sweetened lemonade. This chemical sweetener is easy to mix and retains its sweetness even or months or years of storage. Because it has a bitter aftertaste, it's usually mixed with aspartame (Nutrasweet) or sucralose (Splenda). In sweetener blends each chemical masks the other's aftertaste.
The health concern with using Acesulfame K is that it stimulates the beta cells of pancreas to release insulin. Usually the amount of insulin released is small enough that it does not cause blood sugar levels to fall, resulting in hypoglycemia, but the additional insulin in circulation instead stores fat. This means that if you drink juices or diet sodas containing Acesulfame K to keep your blood sugar levels low but you eat more calories at a meal than your body needs immediately, your fat cells are primed by insulin to store fat just as immediately and with 300 times more than their usual efficiency.
If you don't overeat, the effect of Acesulfame K is minimal. But if you don't have a problem with overeating, you probably don't use products made with Acesulfame K.
If you are looking for a low-calorie way to make lemonade, first of all, make sure you start with freshly squeezed lemon juice. The additional flavor notes from freshly squeezed lemon juice reduce the need for sweetener. Then add just a little “real” sugar with liquid stevia sweetener to taste. It's important not to use too much stevia. Stevia used by itself has a licorice-like aftertaste, but a little white sugar masks any bitter elements in the herb. It only takes about a teaspoon of sugar per glass (about 5 grams of carbohydrate or 15 calories) to round out the flavors of stevia without resorting to the use of Nutrasweet and Acesulfame K.