Wednesday, August 26, 2009

A Year of Intermittent Fasting: ADF, Condensed Eating Window, Weight Loss, And More

Even with intermittent fasting, you should watch what you eat.
Even with intermittent fasting, you should watch what you eat. (Photo by Bryan Bruchman)

I can't believe it's been a year since I started my intermittent fasting experiment. By now, I've gotten so used to it that most of the time it doesn't even feel like an experiment anymore. It's become more like an integral part of my diet.

Which is a good reason to spice things up a little. As I wrote two months ago, I made a temporary change to the experiment and switched from my usual 24-hour cycle of fasting and feeding to a condensed eating window of 6-8 hours just to see what happens.

I found the smaller eating window even easier than alternate-day fasting (ADF). In practice it meant that I skipped breakfast and lunch, and then had a big meal and some snacks when I got home. While at work, I only drank water, coffee and tea. During a 24-hour fast I usually get very hungry and slightly dizzy at one point close to the end of the fast, but skipping breakfast and lunch did not result in a similar feeling of hunger. Sure, I ate with good appetite once I got home, but my energy levels did not drop at all during the day.

I didn't measure my calorie intake, but based on the fact that I gained a kilo during this period, I assume I ate as least as much as I did before. So personally, cramming all of the daily calories into a window of 6 to 8 hours was not a problem. I was already used to eating huge meals, and the eating window was big enough to include lots of snacks or even another meal.

For someone considering intermittent fasting for weight loss, I would recommend either 24-hour fasts or using a shorter eating window than I did. A daily 20-hour fast with a 4-hour eating period improves insulin sensitivity and levels of circulating adiponectin, which are key factors in regulating fat storage and thus weight gain. Further, most of the studies showing benefits from intermittent fasting used an alternate-day feeding schedule.

The implication is that while an eating period of 6-8 hours is probably superior to the usual combination of breakfast, lunch, dinner, and snacks (which keeps your blood sugar constantly high), fasting between 20 to 24 is the choice with more positive studies behind it. This leads me to believe that the most important thing is not how small the eating window is, but rather how long the fasting period is. That is, while eating for 1 hour every 12 hours would technically constitute as a daily eating window of 2 hours, I suspect eating for 2 hours and fasting for 22 yields better results. Whether a 2-hour feeding window and a 22-hour fast is slightly better or worse than eating and fasting for 24 hours is unclear, but what is clear is that both work and that the latter is much easier in practice.

That said, I've been able to both lose and gain weight during my intermittent fasting experiment, depending on what and how much I eat. Anyone who claims that IF allows you to gorge on junk food while losing weight is plain wrong. Combining intermittent fasting with a low-carb diet is, in my opinion, the way to go if quick weight loss is your goal. This way you're getting the insulin benefits from fasting and the lowered insulin response from consuming few carbohydrates.

Another crucial factor would be total energy intake during the eating periods. Based on personal experience and what I've read from other people, there's a tendency to "load up" on calories just before the fast begins, whether you're hungry or not. This makes the fast much easier, because you'll be digesting the food for longer and the hunger won't begin until late the next day. For anyone who wants to get the health benefits of IF (such as reduced mitochondrial free radicals, one of the seven types of aging damage) but maintain their weight, this is probably a good idea, but for anyone else, it can easily render attempts at weight loss useless.

To counter this, my suggestion is to follow the intermittent fasting routine but to eat only when you feel hungry. If the fast is about to begin and you still feel bloated from your previous meal four hours ago, so be it. Don't try to stuff yourself with food as a pre-emptive strike if you don't feel like it. You'll probably feel the hunger pangs earlier the next day, but it'll pass after a few hours, and you'll feel more energetic afterwards.

The take-home message of the above is that despite what you may have heard, intermittent fasting by itself is no guarantee you'll lose weight. It can be used for weight loss, weight maintenance or even weight gain, depending on the implementation: the length of the fasts, the composition of the diet, and total energy intake. By optimizing those three factors, you can shift your weight into any direction you want. By disregarding them, it becomes a genetic gamble.

IF improves insulin sensitivity, which is a good thing, but the relationship between higher insulin sensitivity and weight is not as straightforward as it might seem (more on that later). The easiest way to lose weight for most people is still avoiding a high insulin response in the first place. Reading other people's experiences with intermittent fasting, it seems that most of them have the best results when they combine IF with diets that don't contain refined carbohydrates (including whole grain products), such as Atkins or paleolithic nutrition. When unrefined carbs are brought to the table, the disagremeent over the superior diet begins.

I'm now switching back to my old way of eating and fasting for 24 hours. Further evidence may prove me wrong, but at the moment, I feel that it's more beneficial for overall health than a condensed eating window of more than 4 hours. Squeezing the eating window just seems like too much of a hassle for me, though some people on IF manage to do just that.

I've also done a small experiment with dry fasting (meaning no food or water) and ketosis in my search for the optimal form of fasting, but I'll save that for another post. Meanwhile, I warmly welcome you to post your own experiences with intermittent fasting.

For more information on insulin, fasting and weight loss, see these posts:

Green Tea, Black Tea & Oolong Tea Increase Insulin Activity by More than 1500%
A High-Protein Diet Is Better than a High-Carbohydrate Diet for Weight Loss
Green Tea Extract Enhances Abdominal Fat Loss from Exercise
Slowing Down Aging with Intermittent Protein Restriction

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32 kommenttia:

webster August 28, 2009 at 3:19 AM  

Hi JLL, I found your post on PaNu quite useful in answering my questions, and it looks like your blog will help me answer many more.


JLL August 28, 2009 at 12:53 PM  


Glad I could help, and welcome to the blog!


blingling September 26, 2009 at 11:00 PM  

Hiya, did you lose much weight after a year of intermittent fasting? And if so, how much?
From the sound of your blog post, would seem that as far as weight loss is concerned, it would depend very much on what and how much one eats? But are there any benefits to IF, such as it being easier to control intake/hunger?

JLL September 27, 2009 at 5:48 PM  


My weight fluctuated between 60 and 64 kg during the year. But then, weight loss was not my goal in the first place.

I think intermittent fasting by itself is not the best tool for weight loss -- for that, I would recommend low-carb diets. The combination of IF and LC could be superior to LC, but then, LC keeps insulin levels in check anyway, so it's hard to say how big the added benefit would be.

If one is eating the Standard American Diet, then intermittent fasting will probably result in some weight loss, because you're not constantly keeping your blood sugar high.

And yes, I think there are benefits to IF, regarding self control. First, it ables you to discern between cravings and hunger. Second, it helps you get rid of the fear of hunger. Once you go through that serious hunger for a few hours and realize it doesn't kill you, you'll have a much healthier view of what your body can or can't do. Associating the physical feelings of hunger with positive thoughts ("my stomach churns so that means something good is happening in my body") helps, too.

Anonymous October 22, 2009 at 9:04 PM  

I have been researching intermittent fasting for a while now. I want to do longer fasts, but I want to start with 22hour fasts. I just want to say that your blog helped me a lot, as I worried about low energy levels while at work etcetc.
Anyway, thank you!

JLL October 23, 2009 at 1:02 PM  


You're welcome, glad I could help!

Anonymous December 3, 2009 at 5:09 PM  

I just started my bout with IF. I have not been able to do 24 hours but I have been doing a short window... normally 6-10pm. I do still have energy to work out and normally I eat an apple when I break the fast before any real food. I am doing it for weight loss and a to teach myself how to control what I put in my mouth. Please tell me when you started noticing a difference in your weight. My grandmother did this for years and she's in good health at 73. Will you continue to fast? Is there some type of support site for this type of life style. Are you worried about forcing your body into starvation mode? I have so many questions? I'm looking forward to your insight.



JLL December 4, 2009 at 9:47 AM  


My weight didn't change dramatically during this period, but then, I wasn't doing it to gain or lose weight. I'm sure both options are possible on IF, depending on what/how much you eat -- indeed, I think diet has a much larger impact on weight gain than fasting.

For weight loss, IF does two things: it increases insulin sensitivity (at least in rodents) and teaches self-control. These can get you off to a good start, but a junk food diet combined with IF will probably cause weight gain. So it's not a magic bullet.

I'm currently not doing 24/24 intermittent fasting anymore; I haven't yet decided what I'll do next. I still have fairly long breaks between meals, however.

I'm not worried about starvation mode, and as long as you don't significantly cut back on the amount of total calories you eat, I don't think that's going to be a problem. I think starvation mode (if such a thing truly exists) is only a problem when attempts to lose weight by eating a diet high in carbs but lower in calories. Someone correct me if I'm wrong.

I know there's a Yahoo group that talks about fasting in general; you could try that. And then there's this intermittent fasting thread that I post in once in a while.

Hope this helps,


Anonymous December 23, 2009 at 5:51 PM  


Thank you and Yes this helps. I have started an IF diet( 20fasting/4feeding) and I do see that it takes a lot of restraint but I am conquering it one day at a time. I work out pretty frequently on empty and what I've found is that I'm not hungry afterwards. It completely baffles me. Now I'm more aware of what I'm putting in my mouth and how it impacts my body, mood etc. I also make sure to take a one a day vitamin. I can't tell you enough how encouraging this is, especially considering that fasting is a recommended part of my spiritual growth and I've not been successful at doing it til now.I will continue to watch this blog but are you on any other sites... twitter, facebook etc?

Thanks so much for your response


JLL December 23, 2009 at 11:05 PM  


I notice the same thing too; no hunger after working out on an empty stomach. Though, it depends on how hard the workout is - if it's very light, then I do feel hungry, but if it's hard, then the thought of eating is almost nauseating. I think this is a common phenomenon among bodybuilders. Aerobic training (running, for example) combined with fasting is much harder for me, however, at least towards the end of the fast.

That said, in my case the hunger will make a comeback about three hours after the workout. But if you're feeling really hungry and want to extend the fast, working out is a pretty good way to do it.

icantgoforthat December 27, 2009 at 3:37 PM  

Hey JLL,

Really love your blog. Been making my way through your posts, and also many of your forum posts from imminst. I like your very cutting-edge yet conservative risk-minimisation approach to health and longevity which I very much vibe with.

I was wondering what are your thoughts on a more evolutionary, ad-lib/random approach to eating, fasting, and supplementation?

Instead of a rigid condensed feeding window, or ADF, how about a more Art De Vany stochastic method of eating and fasting, to more naturally reproduce the variation our Palaeolithic ancestors probably experienced?

Anonymous March 4, 2010 at 6:26 PM  

I have been intermittent fasting for around a year now...i have done the 'eat stop eat' syle which is two 24 hour fasts a week and currently i am doing 16 hour fasts with an 8 hour window
I lost several pounds following the two 24 hours fast per week and I ate tons of carbs - the only thing that matters is the calorie intake - you can lose fat fasting intermittingly or on any other 'diet' as long as the your weekly calories (energy) eaten is less than the the calories (energy) used by your body - and your fat stores will provide the balance of enregy . i ate whatever - sometimes healthy, sometimes not so much, but it all comes down to calorie (energy) intake - the problem is the BMR calculatros tend to add alittle to many extra calories - you have to eat very little to actually lose weight - whether this is a healthy way to do it ..i dont know..but it defiantely helps to lose fat - i would recommend liffting wiehgts or resistance training to maintain youe muscle mass
My mother in law is on some crazy diet where she can only eat certain things, very restrictive and it even involves some metabolism pill and shes lost a bunch of weight but its because the diet calls for 900-1000 calories a day...its all in the energy consumed and engery expended...
Mike Phelps eats 12000 calories when he is training and he does gets thiose calories through piizza and pasta, grits - tons of carbs..but its becasue he burns the energy of these foods

Anna March 5, 2010 at 10:31 AM  

I am doing IF 24-hour fasting three to four times a week. That works fine for me. Sometimes I am forced to eat due to social life and gain weight. But when I resume my IF eating habit, my body weight resume normal. IF has been working for me so far so good. It's going to be my 5th year of IF anyway. Thought more people should go on the IF way of eating.
intermittent fasting success

Jasmine March 13, 2010 at 10:10 AM  

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stephanie March 16, 2010 at 8:56 AM  

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Lillea August 20, 2010 at 6:57 PM  

I agree completely that total calories, independent of when/what is eaten, make the difference for weight loss or gain or to maintain. The strictest/best metabolic ward studies show that. There can be problems with edema if someone is consuming foods they're allergic to, or high carb, but that's it. And people with thyroid disease have to consume less, but not by as huge amount as some people claim. I've managed my weight well for my entire adult life (I was born in 1970) by following a variety of "diets" simply by carefully keeping track of calories. When I eat too much, I gain weight. I've tested that by deliberately following a high fat diet and overeating calories, and yep, fat gain! lol. However, the difference between success and failure is hunger, which is the hardest challenge when trying to reduce weight, and that can definitely be reduced greatly with an Atkins or low carb/moderate to high fat Paleo approach, and energy levels can be better overall, after the adaptation period of course. When I was eating low fat, high carb, I had to control my calories with high fiber foods and frequent small meals. Now that I'm Paleo, it's much easier. I can go for a long time w/o eating and not be bothered by hunger to any strong degree. I've been doing a long run of IF daily for 18-22 hrs, usually about 21.5 hrs, with an eating window of 2-4 hours. I too experience light headedness at about the 19 hr mark, which passes within 30 minutes or so. What you posted about when hunger hits you matches what I experience more or less. Very interesting.

Anna October 6, 2010 at 5:01 PM  

I have been on intermittent fasting weight loss since 2006. I am now at the stage of maintaing stable body weight. Even when I gain weight after festival or long weekend crazy eating, once I resume fasting, I'm fine. Though hunger is not really my challenge, I do want to eat everyday. Therefore 24-hour fasting, ie, dinner everyday suits me best. My dinner is usually quite a big meal as I do enjoy eating after a day's fasting. Anna from Fasting For Weight Loss

Lillea October 7, 2010 at 2:56 AM  

I love your site Anna! It sounds like you and I do a similar thing. You look fantastic! I enjoy eating one big meal a day too.

gwarm September 8, 2011 at 12:50 AM  

Do you worry about cortisol going up during fasting being bad for hair ?

JLL September 8, 2011 at 8:45 PM  


I don't know for sure -- but I also don't do 24-hour fasts anymore, since I don't think has the same benefits as calorie restriction (which I'm not doing either).

Anonymous October 6, 2011 at 5:01 AM  

I just came off a 44 hour fast not because i was hungry but doing the fasting for benefits and wondering if going longer 72 hours would have give any additional benefits. during the fast i felt great worked very hard with weights and actually felt stronger.

does any one know of studies that support carb loading one day per week increases testosterone?

Anonymous October 15, 2011 at 11:08 AM  


Eating more than twice a day has been shown to increase risk of colon cancer, A shortened eating window also has been shown to improve health and prevent cancer,, even if you want to go back to 24 hour fasting, you can still eat two meals a day and within 6 hours period, I am fasting twice a week including a daily fast.

Anonymous November 18, 2011 at 8:48 PM  

All I have to say is WARRIOR DIET.
If you want to know about intermittent fasting and:
how to do it right
the science behind it
how to exercise while doing it
how to live a free life with food

Then read this book. It has simply changed my life.

The Warrior Diet By Ori Hofmekler

Venger Satanis February 17, 2012 at 7:45 PM  

Pictures of your progress?

How much can you bench press, squat, and deadlift?

At the moment, I'm going with Martin Berkhan's Lean Gains approach.


JLL March 10, 2012 at 5:58 PM  

@Venger Satanis,

No pictures, and I don't know, I just go to the gym to try to stay in decent shape.


chad aharon April 5, 2012 at 8:22 PM  

What is your workout/exercise schedule?

JLL April 6, 2012 at 1:30 PM  


I go to the gym once a week and that's pretty much it.


DS October 5, 2012 at 4:26 PM  

I fast for about 30-34 hours twice a week,meaning that after dinner on Sunday evening, I have just 500 calories until breakfast on the Tuesday morning. I do the same on Thursdays but am flexible about it if I am going out or on holiday!

It is a challenge but I rarely feel miserably hungry, just a bit peckish now and again but the potential health benefits are huge. I say potential as I know the theory has not been tested but I'm assuming that the results showing lower cancer and other disease rates coupled with increased brain performance are worth it.

I eat what I like the rest of the time and have no problem. I really enjoy my food and don't worry about my weight at all.

Morris Thecat January 3, 2013 at 9:36 PM  

The only weight loss success I have had with intermittent fasting has been when my fasting periods were from 48 to 72 hours. When I am able to maintain a 48 to 72 hour fasting 24 to 48 hour eating routine, then I am able to lose 2 to 4 pounds a cycle

Stefan January 9, 2013 at 1:05 PM  

I have been using intermittent fasting for more than 8 months now. It's not for everyone but it's definitely been the key to losing more than 40 pounds of fat for me. It has made dieting enjoyable for me by keeping my diet really flexible. I used to worry about eating too many carbs etc. but I found that it really doesn't matter that much as long as I keep my protein intake relatively high.

Dukan Diet November 14, 2013 at 8:04 PM  

Have you tried Dukan Diet? What do you think about it? Is it healthy? Is it safe? Thanks for information!

donnagail broussard May 25, 2015 at 4:14 AM  

What about long-term fasting? I've gone 35 days on water and it revolutionized my health. Have you tried long fasts?

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