A Primer on the Fasting Window and Intermittent Fasting

One of the more interesting dietary topics I’ve been learning about over the past several months is the concept of the fasting window, and how intermittent fasting can help you achieve weight loss, eliminate body fat, and improve your body’s overall health and fitness.

Remember, humans only started eating three square meals a day relatively recently. And it’s only over the past century that humans began eating three carb-heavy meals a day.

In contrast, consider a Paleo-era human, genetically identical to human today, yet built to survive, even thrive, in an environment where food was occasionally scarce. A Paleo-era human would periodically go many hours, sometimes days, without eating at all. Which brings us to some of the key central concepts behind intermittent fasting:

1) Our bodies were not designed for the consumption of regularly timed, full-size meals.

2) Our bodies are actually designed for occasional periods of fasting.

3) Our bodies benefit from these occasional periods of fasting.

Bonus! 4) Based on my experiences, intermittent fasting actually isn’t all that bad or even all that hard to do.

A disclaimer. I am not an expert in these areas. Not even close. My goal for today’s post is merely to talk about my own experiments with intermittent fasting. If you’re curious about attempting your own intermittent fasting experiments, or if you’d like to learn more about this domain, be sure to look over the various resources at the end of this post. There’s plenty of reading material there to get you started.

A 17-hour fasting window
So, with that as background: what, then, is a fasting window, and what does it do for you?

Simple: it’s just a period of time during with you don’t eat. And this fasting period causes your body to burn its own body fat through a process called autophagy, where the body in effect metabolizes itself in a way that helps our cardiovascular health, our fitness and our body composition.

Like I said, I’ve been experimenting with intermittent fasting, and I’ll share an example from my own experience of a recent 17-hour fasting window. And while it may seem like a really long time to go without food, it’s actually not as big a deal as you’d think.

First, I had an earlier than normal dinner, finishing eating at about 6:00pm, perhaps an hour earlier than typical for us here at CK. I also made sure the meal was predominantly protein-based. I did my regular post-dinner things: reading, relaxing and so on, but didn’t snack, consume alcohol or ingest anything other than water. Then, I went to bed around 10:00pm.

The next morning I got up at 6:30am, but instead of eating breakfast at my normal time (around 8:00 or 8:30am) I deferred breakfast until after my workout. At 9:30am I went to the gym and did my usual workout, which lately includes things like squats, deadlifts, some light running and other weightlifting exercises. When I got back it was just after 10:30am. I then waited about a half hour, and at 11:00am, I ate two eggs and a dollop of peanut butter, a meal containing about 30 grams of protein and plenty of satiety factor to carry me well into the afternoon.

So, with my simple breakfast at 11:00am, I had just completed a 17 hour fasting window--the time difference between 6pm the night before and 11am the next day.

During this time, my body first obtained fuel from my meal from the night before. At some point, however, it began extracting the fuel it needed from my body’s own stores of body fat. Which is the whole point of all of this in the first place.

What was most striking about this 17 hour fasting window, shocking even, was that I was never hungry at all, thanks to two things:

1) a high-satiety, low-carb meal the night before,
2) the fact that working out makes your hunger temporarily disappear.

I only really started to think, “hey, it might be kind of nice to eat something” at around 10:45, just a few minutes before I actually ate.

One more thought. Every time you sleep through the night, or at least avoid creeping downstairs and raiding your fridge in the middle of the night, you execute a fasting window of around eight hours. Which means the easiest way to apply intermittent fasting is to incorporate your sleeping period, but then add a couple hours of extra fasting on either side. Start by eating a slightly earlier dinner and deferring breakfast a little the next day. This can get you to a simple ten- or even twelve-hour fasting window quite easily with minimal changes to your routine. Try it.

Once again, we humans weren’t designed to eat every few hours--as much as we tend to get hungry with that kind of timing and think we need to eat. We certainly weren’t built to eat regular, full-size meals consisting of carb-heavy processed foods. And, in an unfortunate case of dietary circularity, it’s the carb-heavy foods themselves that put us on a hunger roller-coaster, making us think we need more food every few hours.

Finally, I’ve repeated this intermittent fasting experiment many times in the past few months, with fasting windows ranging from 12 hours to 19 hours, to see what the results would be. At what point I feel unwell? Would I ever experience severe hunger?

The answers, shockingly, were never and no. I experience some modest sensations of hunger once my fasting window gets beyond 16 hours, but nothing severe and nothing I couldn’t handle. Further, it was interesting to have a chance to observe those mild-to-moderate sensations of hunger. If anything, they were good tests of my Stoic principles, which made me all the more grateful and appreciative of the food I later ate.

Read Next: Minimum Viable Progress

Resources/For Further Reading:
1) The New Evolution Diet: What Our Paleolithic Ancestors Can Teach Us about Weight Loss, Fitness, and Aging by Arthur De Vany, a pioneering thinker of Paleo eating and fitness.

2) Man 2.0 Engineering the Alpha by John Romaniello and Adam Bornstein. Extraordinarily useful (though male audience targeted) book on fitness and diet with excellent discussions on fasting techniques.

3) Antifragile by Nassim Nicholas Taleb (the entire book is useful, but specific to fasting see pages 365-369).

4) Highly useful four-part series on various aspects of intermittent fasting at Inside Tracker: Part 1, Part 2, Part 3, and Part 4.

5) See also CK’s ragingly positive review of Arthur De Vany’s The New Evolution Diet

6) CK on how to apply “Antifragility” to our diets--and eat better for a lot less money.

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Marcia said...

I've always been interested in the whole IF idea. I have to admit, though, it doesn't work for me.

Then I did a little reading and research about fasting for women. Turns out, it can really mess you up with stress, cortisol, fertility, menstruation, etc.

Daniel said...

Hi Marcia,
Agreed that anything done unwisely or to an extreme can mess you up, and again, I'm no expert in this domain. But I'd take it back to first principles: both paleo "man" and paleo "woman" lived in the same environment, and neither were designed for the modern era's high-carb meals, at rigid intervals, every few hours. Thus I don't see any reason a woman can't make some tentative experimentation in this direction... just as well as a man can.


chacha1 said...

I sorta kinda do this every workday. We're generally done with dinner by 8:00 p.m. and I don't generally snack, or drink (anything but water), between dinner and bedtime. I get up between 6:30 and 6:50 every day thanks to the cats. I don't have breakfast until 9:30 or 10:00 most workdays. That's only a 13-hour fast, but physically I can really tell the difference if I eat dinner later or breakfast earlier.

Purely anecdotally, I know a lot of women who struggle with their weight and they almost all eat dinner later and/or breakfast earlier than I do. I consider it part of my lifetime weight management protocol. Even now, at 50, as long as I am not eating/drinking later in the evening, I don't really have to micromanage my calories. And I am not an athlete or gymgoer, my daily exercise regimen hardly looks like exercise at all.

To me this seems like such a simple thing to try that, if a change is needed, why not try it. This is not in the same league as the dangerous "cleanses," where you don't consume anything except some nonsense like lemonade with cayenne, for 2-3 days.