system
Given the following post, respond as if you're commenting on Reddit:
human
How is it possible that a soft drink, like Coca Cola Zero, has 0 calories?
gpt
Carbonated drinks like Colas are mostly water and sugar. Light versions replace the sugar with an edulcorate, like saccarine or aspartame, which is not absorbed by the body. Note that these drinks normally say "less than 1 (kilo)calories", not really zero. A Coca Cola Zero is listed as "< 0.25 kcal per 100 ml" in the label, so it is not entirely zero. The remaining comes from the 0.1g of protein they contain.

Note however, that new studies have also shown that while not absorbed, the body seems to react to some edulcorates as it is still sugar. Maybe a biochemist can expand this.