system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How long does it take for food to “store as energy” (fat) within a human body? Why does the body burn muscle instead of fat when starving?
gpt
Think of fat like a savings account, and muscle mass as expenses. If you spend a little more than you take in in a particular month, you can withdraw a little from savings to cover the difference. But let's say you lose your job and have no money coming in (Starvation). Spending your savings is only going to work for so long, but you can extend that length of time by spending less money (reducing the amount of muscle mass). This way gives you longer to find a source of food to save your life.