system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do they make bubly, lacroix and the like 0 calories with natural flavour.

Shouldn’t natural flavour have calories?
gpt
All kinds of fruit juice have calories in them, and most of the calories come from sugars. But it's possible, using various tricks of chemistry, to separate the sugars from the other compounds which give the fruit its distinctive flavour and aroma. (Generally these are compounds detected by scent, rather than taste.) So if you get those fruit flavour chemicals separated out on their own, and add them to carbonated water with some no-calorie sweetener, then you've got a lacroix. And if you got those chemicals from a fruit in the first place, then you're allowed to call it a natural flavour. (often there are also some other rules you must stick to in order to use that label, but it depends where you live.)

edit: Also, it's sometimes possible to extract flavour-bearing compounds from other parts of the fruit than the sugary juicy part. Lots of natural orange extracts, for instance, are made from the peel.