Don't worry. Although they are pure carb, the quantity you use weight wise is Tiny, which is why they work. They are hundreds of times sweeter than sugar. REMEMBER, you use canderel powder with the same number of teaspoons (or a bit less) as you would sugar, not the same number of GRAMS as you would sugar.
Quick example by the way dougie. My ice cream recipe calls for 70 grams sugar. That's 14 teaspoons and 70 grams carbs. 14 teaspoons of canderel weighs about 8 grams, so about 7.5 grams carbs. I would use about 10 teaspoons canderel, about 5 grams carbs.
By the way dougie, for ice cream there's a "no added sugar strawberry syrup" by "crusha" you can get at sainsburys and tescos. Virtually no carbs. Designed for milk shakes, but works great with the basic ice cream mix in an ice cream maker. I make up about 5 separate little pots at a time and keep them in the freezer. Just take a pot out 30 mins before you want it