system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Losing Fat (When does it happen?)

Why can you weigh less when you wake up, and when does fat actually leave your body? Do you process it out (waste) or what?

Edit to clarify: I don't want "how to lose weight" or "your body burns it off". Looking for the biological process of "burning it off" or what happens.
gpt
The actual elements making up your excess weight are excreted through 4 main channels: Sweat, breathe, urination, and pooping.

Most of it, surprisingly, is your breathe. You breathe out CO2. What's the C? Carbon.