My go-to answer in the past was, it depends on your own body chemistry…
One person’s biggest insulin drop (lower insulin = better fasting results!) may occur at a different time than another person’s…
Everyone’s metabolism is slightly different, so while everyone can benefit from IF, the best schedule and eating window varies from person to person…
At least, that’s what I thought!!
But then I saw a study from the 90s that still makes a lot of sense today, showing that you can get a lot of benefits from fasting at least 18 – 24 hours.
I know, all you 16:8 fans are probably saying, come on!!
Let me explain the reasoning with a bit of science!
So, first off, what does being in a ‘fasted state” mean in science-speak? It means:
As you probably already knew, this happens 8 – 12 hours after you’re done eating.
Exactly how many hours it takes to be fasted varies a bit from person to person, and also depending on what you ate (high-carb = longer!).
So, how long should I fast??
Here’s where it gets interesting…You’d think the 16:8 schedule is good enough, because you’re in the fasted state for a few good hours!
But, the problem is, your insulin levels are still too high to experience mass fat breakdown!
One IMPORTANT component of the fasted state that a lot of people don’t know about is, the effectiveness of the fat loss and cell autophagy depends quite a bit on your insulin level…which KEEPS DECREASING the longer you fast!
So, when you’ve fasted for 16 hours (and been in the state for 4 hours) your insulin is still higher than it could be…it will continue to get lower the longer you go…
And that lower insulin means that your fast will burn fat!!
(Within reason, of course. If you look at the chart from the study, you’ll see that if you try to go much longer than my 60-hour fast, your insulin starts to spike back up again. Not a good move!)
If you’re asking “How long should I fast”…
The answer is still up to you! Whether you’re a fan of the 5:2 diet, fasting two days a week, or you want to expand or contract your eating window.
I say, trial and error is your friend, and then go with whatever makes you feel great! That is the end goal, after all, and it’s easy to lose sight of that when you’re thinking about maximizing health, performance, results…
So, I don’t want you to get obsessed here. But I think it’s so, so worth mentioning that being in a fasted state for longer reduces your insulin levels, which directly causes fat loss and cell autophagy to be more efficient.
And, of course, it’s not just about reaching peak fasted-state awesomeness, but also just…y’know…being in the fasted state is good for you!
For that reason alone, 16:8 is great, but 18:6 or 20:24 is just a little bit better.
That’s my NEW go-to answer for “how long should I fast”!
There’s no better feeling than finding a way to improve on your IF…finding a way to improve even more on something already great you’re doing for your body!