1) 16/8 Extended Overnight Fast (aka Leangains protocol)
This version is very widely used and is arguably the easiest version of IF. If you skip breakfast anyway, you would barely even notice this fast.
It works by eating within an 8-hour window each day. Doing some quick maths, this means you fast for 16 hours a day.
This is a great option to try if you’re new to the whole fasting thing. It doesn’t matter when your 8-hour window is in the day, the benefits will be the same. You could do breakfast at 11am and end on dinner at 7pm. Or 10am-6pm, or 9am-5pm. You get the idea. It’s flexible.
Some people shorten the window down to 7, 6 or 4 hours, at the very lowest. This is obviously much harder to stick to, and it’s not recommended for beginners to start on a 4-hour window. (Read all about what happened when I did just that in the euphemistically named IF: A Learning Curve)
The major plus of the 16/8 fasting method is that you’re asleep for a lot of the fast. This method requires way less willpower than going all day without eating anything. It’s also more likely to be sustainable.
2) Whole Day Fasting, or Eat-Stop-Eat
Whole day fasters commit to a full 24 hours of not eating. They usually fast from a mealtime one day to the same mealtime the next day. So, you might have dinner at 7pm and then no food until the following day’s dinner at 7pm. Breakfast-to-breakfast and lunch-to-lunch work well too. Benefits are the same.
This is definitely not an everyday thing, and best kept to once or twice a week.
As you can imagine, whole day fasting requires a good amount of willpower. Not eating for 24 hours can be really tough. This is advisable for more advanced fasters, and is not a great place to start your IF journey.
That said, there are many, many people who swear by the eat-stop-eat method, and report feeling absolutely mint. There’s mounting evidence to suggest whole day fasts can significantly improve your body’s metabolism and even longevity. (Yes, fasting could help you live longer.)