system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why doesn't the body use up its fat reserves before it gets hungry and dizzy?
gpt
Historically, fat was meant for emergencies only.  A last-ditch reserve to maintain life when food is scarce.  The hunger motivates you to eat so you don't have to dip into this emergency reserve.  The dizziness is because you take as little energy out of your reserves as is needed to maintain life.  Having low energy makes you feel dizzy and faint.  Your body doesn't know whether you're going a few hours without food or a few days, so it plans on the worst case scenario.