system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:ELI5: When a person exercises and burn calories, what is actually happening to the fat? when someone loses weight where is the fat going?
gpt
Your fat is made of hydrocarbons - molecules of hydrogen, oxygen, and carbon.  When you inhale oxygen (O2) and exhale carbon dioxide (CO2) you are literally exhaling the carbon from those fat molecules as you burn those calories.  What about the hydrogen and oxygen? That becomes water which you urinate/sweat out.