system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When your body decides to use fat for energy.How does it decide which part of the body the fat should be taken from?
gpt
Your body builds/burns fat at  predisposed, but pretty much random locations. Fat is a necessary insulator as well as energy source, so your body needs it everywhere, not just in specific places. This is why you can do crunches every day and never see a difference in belly size, but a significant drop in your thighs. (it's obviously important to exercise various muscle groups {all of them, or at least try for it} if you want to "shape" your body.)