system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the body naturally wake up around the same times every day without any prompting, even if it hasn't been 8 hours?
gpt
Nobody precisely knows.

It’s a popular research subject.

A Harvard study found that fasting for 16 hours followed by waking up and eating had a good chance of resetting your internal clock to think that meal was “breakfast”, and you’d start sleeping and waking up accordingly.

Why this happens is not clear, but it’s an experiment I’ve tried and it does tend to work.