Intermittent Fasting and Circadian Rhythms

I had a blog idea comparing various cleansing/detoxification schemes with intermittent fasting, with the gist being that there are some similarities. Both probably make you feel better for largely the same reasons, but that fasting is better and free. With detoxing and cleansing, it seems that someone is always trying to separate you from your money in some way.

So anyway, I’m still planning that blog and in doing so I thought I would look up what “” had to say about both. Generally they hate everything alternative, and predictably they put the smack down on cleansing/detoxifications for reasons I largely agree with. I was somewhat surprised to see they seemed overwhelmingly positive yet cautious about intermittent fasting, again for reasons I overwhelmingly agree with. Intermittent fasting really is getting a lot of science behind it, and my own experience has been (and continues to be) pretty great.

So anyway, that’s not what this blog is about, but in reading the article on fasting, it cited a study about circadian rhythms that I have been looking for data on for some time. It’s funny, you go to enter in your search terms and things don’t always just pop up as you want. So anyway, here’s the paper I wanted to talk about with comments to follow:

The internal circadian clock increases hunger and appetite in the evening independent of food intake and other behaviors. Obesity (Silver Spring). 2013 Mar;21(3):421-3. Scheer FA, Morris CJ, Shea SA.

From the Abstract

There was a large endogenous circadian rhythm in hunger, with the trough in the biological morning (8 AM) and peak in the biological evening (8 PM; peak-to-trough amplitude = 17%; P = 0.004). Similarly-phased significant endogenous circadian rhythms were present in appetites for sweet, salty and starchy foods, fruits, meats/poultry, food overall, and for estimates of how much food participants could eat (amplitudes 14-25%; all P < 0.05).

In people who sleep at night, the intrinsic circadian evening peak in appetite may promote larger meals before the fasting period necessitated by sleep, whereas the circadian morning trough would theoretically facilitate the extended overnight fast. Furthermore, the circadian decline in hunger across the night would theoretically counteract the fasting-induced hunger increase that could otherwise disrupt sleep.

My comments:

This was interesting to me because I first learned about intermittent fasting by reading on wiki “The Warrior Diet”. It turns out that wasn’t true fasting because Ori Hofrichter ate (but ate in smaller amounts) during the day. I later became a fan of the Fast-5 diet because it was simpler. Bert Herring was a real faster, because he ate nothing during the day.  It also helps that Burt gives his book away, and even better, he didn’t try and sell you on hundreds of dollars worth of supplements every month.

The thing that appealed to me was not having to prepare any meals, healthy or not, during the day, and just being able to eat as I wanted at night. Still I think both Ori and Bert were on to something about consuming the bulk of, or all of your calories at night. Night time seemed when most people want to eat. As such, I think when people try to lose weight with a lot of small meals as is typically recommended, you’ll be taking in some of those calories when you aren’t really hungry, or are otherwise busy. Then at night when you really are more hungry, and the refrigerator is right there, you have to chose between cheating or suffering.

I also think the circadian rhythms would go a long way towards explaining eating disorders such as binge eating and bulimia, where the binge and subsequent purge is generally at night. While it hasn’t been researched yet, I have this suspicion that time restricted feeding with a night time eating window, is God’s gift to both disorders. Though probably not anorexia, where eating more calories is necessary.

With the time restricted feeding variety of intermittent fasting, your eating won’t interrupt your day, that way at night when you are most hungry you can have big, satisfying meals. I had always thought this was the most efficient way to go, and the most psychologically satisfying. At the end of the day, you still had your big meal/reward to look forward too. If I recall correctly, Ori in The Warrior Diet talked about eating at night being the most natural, arguing that, lions have to be cunning and alert when hungry (in sympathetic mode), and then can relax after eating (in parasympathetic mode). This is something I never saw any research on, but I find his logic compelling.

Finally I came across a paper that kind of backs up his theory that night eating is the most natural time to do it, and that there is more to it than psychology and convenience. 8 am is when we are least hungry, and our hunger peaks at 8 pm every night. The Warrior Diet’s 4 hour window of eating most of your food from 6-10 pm seems to hit that just right. The same is true of the Fast-5’s typical window of 5-10 pm. For what it’s worth, I now hybrid the two, eating all my calories in a 4 hour window like Ori, with no small meals like Burt, and it’s just as easy.  

So to sum it all up, what’s that you hear about breakfast being the most important meal of the day? That’s called propaganda.

Thanks for reading my blog. If you have any questions or comments (even hostile ones) please don’t hesitate to ask/share. If you’re reading one of my older blogs, perhaps unrelated to neck or back pain, and it helps you, please remember SpineFit Yoga for you or someone you know in the future.

Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed Yoga Teacher Training at Sampoorna Yoga in Goa, India.


3 responses to “Intermittent Fasting and Circadian Rhythms”

  1. Leha Carpenter

    Thank you. This validates the only kind of diet or CR that has ever worked for me. The other thing is, once I start eating, whether it’s at 8AM or 8PM or somewhere in between, from that point forward, I will get hungry at regular intervals; which makes any kind of CR an intense test of willpower if I eat during the day.

    I hadn’t read The Warrior Diet, but the part about the lion needing to stay alert during the day makes sense for a diurnal species. None of us wants to be caught in rest and digest when we should be in fight or flight. Maybe he should call it the “worrier diet.” 🙂

    BTW thank you for all your great content and insights here–I came for the EMS info, and am learning all kinds of other stuff.

  2. Giuliano


    Love your site. I have recently begun IF (5hour window) and have been going strong for about 3 weeks. I seem to be struggling in hitting my target weights and reps as I have to lift during a fasted state. Should I change my window? Is lifting in a fasted state counterintuitive to increasing strength? I’d like to know your thoughts.

    1. Chad Reilly

      Hi Giuliano,

      Thank you for the compliment about my site! The 5 hour window is what I started with, then I went to 4 but usually just eat one meal in about an hours time and call it good. Regarding training fasted, I think it’s something you get used to, and after 30 days is when the increased energy from fasting starts to kick in so I bet in a couple more weeks you’ll be used to it. I would even workout in the mornings or over lunch and still not eat until my evening window starts at 5-6 pm. Once I was used to it I was no weaker. Most people who are doing the fasting for bodybuilding try to have their big meal right after they workout, and I expect that is optimal for size gains. But even with my window being hours later (done out of convenience and because it fit my lifestyle) I was still able to gain muscle. I just had to eat a lot in my window, and I added whey protein just in case. I hope that helps!

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