system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How fast can anyone physically gain body fat?
gpt
Less than 30 seconds.

If you drink sugar after fasting for 12 hours, that sugar will appear as fat in your liver 30 seconds later.  It probably happens faster than that, but that's how long an MRI scan takes.  Essentially if you drink a big glass of sugar water on an empty stomach, some of that sugar will be fat before you finish drinking.