system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can 100% orange juice have calories but something like flavored sparkling water containing fruit juice have no calories?

Even if the amount of fruit juice in the water is small, it's still calories, isn't it?
gpt
There is sugar in an orange so there are calories in an orange.

The sparkling water might have an sweetener that our bodies cannot digest (= 0 calories), or one that does not need very much to achieve the same level of sweetness that sugar does (<5 calories = 0 calories).