system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does intermittent fasting work?

Why does it work? Is it safe? How do you do it?
gpt
Intermittent fasting is when you don't eat for a determined amount of time, and eat all of your calories during an 'eating window'. 

Eg: fast for 16 hours, eat for 8. Repeat every day. Most people do this by skipping breakfast and lunch, and eating around dinner time. Or you can do a 24 hour fast every 3 days or so. There are a ton of variations that you can look up.

The whole idea is to deprive your body of external energy sources so that it can dig into its internal energy sources aka your fat tissue. The concept is there but most of the information we have about it comes from people's subjective experiences whereas the scientific literature haven't found any significant differences in terms of fat loss between people who do IF, and people who simply calorie restrict. Yes, it is considered to be safe when done right. It's just another way to control your eating habits and cut some fat. As long as you hit your daily caloric and macro goals, and eat good foods, you're safe. A lot of people report reduced craving for junk food on the days they fast, but for others IF triggers episodes of binge eating. So it really comes down to what works for your body and lifestyle.