Monday, March 23, 2009

Intermittent Fasting: Understanding the Hunger Cycle

Intermittent Fasting: Understanding the Hunger Cycle
Coffee can be your foe and your ally during a fast. (Photo by DeusXFlorida)

In this update on my intermittent fasting experiment, I will share some of my experiences with hunger. If you're interested in giving fasting a go but doubtful whether you can live with the hunger, you may find the following information useful.

For those who haven't read my previous update, here's a quick recap. For the past eight months now, my eating schedule has been a cycle of 24 hours of eating followed by 24 hours of fasting. This diet is known as intermittent fasting (IF) or alternate-day feeding (ADF). In case you're wondering why anyone would willingly restrict their eating, see my posts on intermittent fasting and caloric restriction.

After trying a few variations, the point where I either start or break the fast has naturally gravitated towards 6 PM. On the days when the first part of the day consists of eating and the second part of fasting, this allows me to eat one more meal at home after work before beginning the fast. While making it without food to 6 PM is somewhat more difficult than to, say, 4 PM, it's not impossible at all. Hence, six o'clock seems like a good compromise.

I've followed the diet cycle pretty strictly, but I don't stress it if my schedule doesn't fit with a fast. For example, if I know I'm going out for dinner, I might switch the fasting days with the eating days or adjust the time by a few hours. Sometimes on weekend nights, I've also had fasts where I don't eat anything but do drink alcohol (which I like to call intermittent fasting with beer, or IFB). The bad part is the seemingly illogical "how come I'm consuming liquid energy but keep feeling hungrier" sensation; the good part is that you get a buzz from drinking much less.

These months of various degrees of hunger and satiety have taught me a few things about fasting I'd like to share. I assume most people are reluctant to try IF because they're afraid they won't be able to endure the hunger. However, I can honestly say that after the first few weeks, the hunger is really not that bad.

There is also a smaller cycle within the larger cycle of eating and fasting; namely, what I like to call "the hunger cycle". What the hunger cycle means is that the feeling of hunger during the 24-hour fast is not constant but fluctuates as time progresses. In my experience, the variation is not random. Instead, there's a clear pattern that becomes evident after a while. Knowing this pattern can be very helpful when you're doing or thinking about doing intermittent fasting.

Fasting hours 1-4: 6 PM - 10 PM

My last meal (sounds more dramatic than it is) before the fast is usually big enough to keep hunger away for several hours. In fact, I make it a point to eat a lot right before the fast for precisely this reason, so it's hardly surprising that the first four hours pose little problems in terms of hunger. I also drink a few cups green tea or black tea right after the meal both to keep insulin levels healthy and in anticipation of the next few hours.

Fasting hours 4-8: from 10 PM to 2 AM

During the four hours before bedtime I get the first small cravings. Since I know I've already consumed my daily calories, I can easily tell that what I'm feeling is not real hunger but a slight psychological craving to eat something. Dark chocolate especially seems like a good idea at this point. Although I avoid drinking tea this late, the few cups from earlier seem to carry over their slight hunger-reducing effect a little and help create a fuller feeling. Water is also good.

Fasting hours 8-15: from 2 AM to 9 AM

This is when I get my sleep on. No problems with hunger here.

Fasting hours 15-17: from 9 AM to 11 AM

Interestingly, when I wake up, the cravings from the previous night have usually disappeared, so skipping breakfast is no big deal. I usually also feel very energetic at this point, even though I never used to consider myself a morning person. When I get to work, I drink a cup of coffee and almost always feel a noticeable lift in mood. The high energy level and good mood are not accompanied by feelings of hunger, which makes this one of the best and most creative periods of the fast.

Fasting hours 17-19: from 11 AM to 1 PM

Here's when hunger makes its appearance. Energy level is still pretty high, but looking at colleagues having their lunch really makes the stomach growl. I don't feel fatiqued at this point, but food seems really tempting. Nonetheless, this is still a period in which to get things done.

Fasting hour 19-20: from 1 PM to 2 PM

The dreaded 20th hour arrives. Even though I wouldn't pass on an offer for late lunch here, the cravings are less pronounced than a few hours earlier. The hunger is replaced by a strange brain fog and general lack of energy. Things that require concentration become difficult, and I often find myself staring blankly at the screen. I usually drink a cup of green tea, but it's of little use. Coffee is not a good idea, because instead of having the mood-lifting and energy-giving effect of the morning cup, caffeine will only make the dizziness worse.

Fasting hour 20-24: from 2 PM to 6 PM

The fog gradually lifts, with the feeling of hunger making a comeback (though this time it's more of a cameo appearance than a leading role) and energy levels increasing again. This is another very nice period that gets better and better towards the end of the fast. Creativity seems to increase, and there's a general feeling of lightness.

What's funny is that right before it's time to finally break the fast and eat again, it feels like continuing the fast would be quite easy. And in fact, sometimes when I have continued it into the 24-26 hour range to adjust the schedule, I've felt very good. The reason I don't usually fast for more than 24 hours is because I would have to keep adjusting the point where I start or stop eating. And of course, when the first meal of the day is in front of me, I'm glad that the fast is over.


The feelings of hunger during intermittent (24 hour) fasting vary with time. The one thing to keep in mind is that, in my experience, the most difficult part is near the 20th hour into the fast. That's when the hunger is replaced by a general lack of energy and focus. This feeling will, however, pass in an hour or so, after which fasting becomes much easier again.

For more information on intermittent fasting, see these posts:

Intermittent Fasting with a Condensed Eating Window – Part I: Poorer Insulin Sensitivity and Glucose Tolerance?
Intermittent Fasting Reduces Mitochondrial Damage and Lymphoma Incidence in Aged Mice
A Typical Paleolithic High-Fat, Low-Carb Meal of an Intermittent Faster
Intermittent Fasting Improves Insulin Sensitivity Even without Weight Loss

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3 kommenttia:

Anonymous July 29, 2010 at 6:06 PM  

I have found your posts quite inspiring. Because I am a student, brain fog, or fear of it, is the main thing that has kept me from IFing more often.

To what extent has this hunger cycle changed since you've began IF? It seems from this post that the fast is always a little hard psychologically, and the period of brain fog never completely vanishes, even after several months of ADF.

What do you generally end up doing during the 20th-hour period? Do you just stare at the computer screen and drool? Or are there other things you have found it possible to do adequately even through the fog?

Do you find it becomes harder to maintain the IF during periods of psychological stress, particularly work-related?

It sounds like your approach to work during a fasting day is generally to accomplish a lot in the morning and early afternoon, in anticipation of accomplishing much less the rest of the afternoon and perhaps nothing in the evening. Is this correct? And, to what extent do you think ADF has affected your work performance overall?

JLL July 30, 2010 at 2:25 PM  


Have you checked this post:

How to Deal With the 5 Most Common Difficulties of Fasting

The hunger cycle didn't change significantly after the first two months or so. The period of brain fog was definitely there even after a year. Some people apparently don't experience it, but I did. If possible, I'd just sleep through the brain fog or do something that doesn't require mental effort. Walking outside in fresh air is pretty good.

I don't find IF harder during stress. In fact, it may even be easier -- when I'm busy working on something, it takes my mind off food and hunger, and brain fog excluded, I'm able to concentrate better. It's when I'm bored and stress-free that I start thinking about eating just for fun.

And yes, it's easy to get things done in the morning and early afternoon when fasting. Though I'm not doing the 24/24 hour cycle anymore, I often still fast on the mornings, because I feel like I have more energy and motivation to get things done.

Overall, the effect on work performance has been positive in my opinion. Still, skipping breakfast and lunch is even better in terms of work performance, because doing 24/24 IF, every other day means big breakfasts and lunches, which reduces my work performance.


Anonymous January 21, 2012 at 3:42 AM  

Alcohol increases insulin and lowers blood glucose. Hence, you feel hungry after drinking.

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