system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If you are overweight, why can’t you live off of your fat preservatives and function normally?

If bears can hibernate and live off of their fat in the winter, why people who are overweight still get nauseas if they don’t eat?
gpt
You can live off it. That doesn't mean it'll be pleasant in the meantime. Your body  generally wants to keep you alive - if you're not doing important things like eating, it's going to make you feel bad until you do. 

Over a longer period of time, you'll start running into issues with some vitamin/mineral deficiencies and such as well.