What I’ve Learned From Two Years Of Intermittent Fasting

What I’ve Learned From Two Years Of Intermittent Fasting

Adopting a philosophy of self-experimentation can make a tremendous difference in your life. Choosing to experiment with new ideas can help you start a successful business. Choosing to experiment with sharing your work can launch your career as a writer or an artist. And choosing to experiment with different diets and workouts can help you discover a fitness and health strategy that works for you.

Image remixed from Skylines (Shutterstock).

This post originally appeared on James Clear’s blog.

Of course, self-experimentation is exactly the opposite of how most of us want to approach things. We would prefer that someone hand us a one-page sheet with the answers to our problems and say “Do this and you’ll be good to go.” Furthermore, if someone shares an idea that seems outlandish or weird, most of us would rather dismiss it than experiment for six months to see if it can actually work for us.

Just to be clear, I’ve made my fair share of mistakes and have dismissed ideas without trying them in the past. But in the case of intermittent fasting, which I’ll explain below, I’m glad that I decided to do some self-experimentation and see if it would work for me. I’ve been experimenting with intermittent fasting for more than two years and this is what I’ve learned.

Intermittent Fasting: What It Is and How I Do It

Here’s a simple definition of intermittent fasting: you eat your normal amount of food in a smaller time frame. It’s not a diet, it’s just a pattern of eating that reduces your eating window each day to about 8 hours. For example, I usually eat my first meal around 12pm or 1pm and then I can continue eating until my final meal at 8pm. After that, I fast until the next day at 12pm. That breaks out to about 16 hours of fasting and 8 hours of eating each day. I do this almost every day. (My guess would be that I do intermittent fasting 350 out of 365 days per year.)

I’m not going to dive into the details of intermittent fasting in this article. I have previously written a 3,000 word beginner’s guide to intermittent fasting and a lengthy question and answer guide on intermittent fasting. If you have questions about how it works and the science behind it, read those articles. And if you want even more information, I was also interviewed on the Fat Burning Man podcast (here) and the Jimmy Moore’s live show about intermittent fasting (mp3 download here).

The Biggest Benefit of Intermittent Fasting is Simplicity

In an interview with Vanity Fair, President Obama described an interesting strategy he uses to make his life simpler. “You’ll see I wear only grey or blue suits,” he said. “I’m trying to pare down decisions. I don’t want to make decisions about what I’m eating or wearing. Because I have too many other decisions to make.”

What President Obama is referring to is a concept called “decision fatigue” and it can drastically impact your ability to make decisions throughout the day. I explained the science of decision fatigue in this article. For the President, simplifying his clothing choices is a way to make life simpler and improve his decision making abilities.

For me, intermittent fasting provides the same benefit. Eliminating breakfast and not thinking about food until 12pm each day has allowed me to reduce the number of decisions I make in the morning, thus reducing decision fatigue and increasing the willpower I have for the rest of the day. That means I have more energy to put toward doing work that is important to me. One of the best ways to find happiness and success in life is to strip away the unnecessary things and focus only on what is needed.

With intermittent fasting, I have been able to increase strength, reduce body fat, and maintain good health while spending less time eating each day. If you can get the same results by making life simpler and only eating twice per day, why would you make life more complex by eating three, four, or five times per day?

Intermittent Fasting is an Excellent Travel Strategy

I used to be annoyed by the lack of healthy food options in airports. This is especially true in my case because I’m looking bulk up and add good weight, so I need to eat a lot. Finding a sizable amount of healthy food is a tall task in most airports. The solution? Treat your travel days as a fasting day and then eat twice as much good food the following day.

As an example, last year when I was flying back from Thanksgiving with my family, I didn’t eat that day. It ended up being about 32 hours between meals. That’s the longest I’ve gone on a single fast, but things worked out just fine and I avoided the poor nutrition of the airport.

So Far, Intermittent Fasting has Not Hurt My Long-Term Health

I’m not interested in doing intermittent fasting if it sacrifices my long-term health for short-term improvements. And for that reason, I’ve kept a close eye on how I feel, how my body is responding, and whether my overall health is improving or declining. Thankfully, I’m in better shape than I was two years ago, which is proven by my strength numbers in the gym.

And more importantly, a recent checkup with my physician has revealed that my blood work, cholesterol, and hormones are in check as well. And remember, this is after two years of intermittent fasting. (If you’re interested, my recent blood work results are here.)

Note: I think it’s important to clarify that I can only speak from my experience and I can’t promise anything with regards to how your body will respond to intermittent fasting. I know that, in some cases, women believe that intermittent fasting has thrown their hormones off balance. I don’t have any data on this and so all I can offer is my own experience. As with most things in life, your mileage may vary.

Intermittent Fasting Isn’t a Magic Pill

In the beginning, I hoped that intermittent fasting alone would be a secret weapon for health and fat loss. It seemed like all of the experts were saying that if I changed what time I ate, then I would lose fat and gain muscle easily. That sounded good to me. The reality, of course, is much different. I only started seeing the results I wanted when I combined intermittent fasting with a healthy diet of real, whole foods, and consistent weightlifting.

Intermittent fasting is just another tool in your toolbox. Just as eating a healthy diet of real, whole foods is another tool. And exercising regularly is another tool. And meditating or doing yoga to reduce stress is another tool. And sleeping at least 8 hours per night is another tool.

You can’t live an unhealthy life in other areas and expect one thing to solve all of your problems, but you can slowly add a piece here or there, continue to self-experiment, and gradually develop a health strategy that works for you, your goals, and your lifestyle.

In fact, I’m convinced that you can reach your health goals without intermittent fasting at all (if you eat properly and train consistently). But I still think intermittent fasting is worthwhile because, as I said above, if you could get the same results while eating fewer meals and making life simpler, why would you add more meals and make life complex? On a related note, if you’re looking for a simple way to eat healthier foods check out my “outer ring” strategy in this article.

I Have No Idea if Intermittent Fasting Will Work for You

I can’t say whether intermittent fasting will work for you. All I know is that, as one piece of my overall strategy, it has worked for me. It works because it fits my lifestyle. It works because it is simple enough for me to not spend much energy thinking about it. And it works because it aligns well with my diet, which is mostly Paleo, and my training style, which is mostly Olympic weightlifting and other compound movements.

If you’re eating poorly or if you’re training for an Iron Man or if your job doesn’t give you the flexibility to eat your meals in an 8-hour window, then intermittent fasting might not be for you. And that’s fine. You can experiment with other ways to achieve your goals.

Where to Go From Here and What Actually Matters

No one will have the same experience as you — with intermittent fasting or with anything else — and that’s why you have to experiment on your own. It might be easier to cite a study or follow the advice of some diet guru, but the only way to get results is to test, adjust, and repeat. As someone who often cites academic research in their articles, I have the utmost respect for science. But you can’t let a research study make choices for you. They can inform you, sure. But the only way to make progress and change in your life is to make new choices, take action, and make adjustments based on the results.

Whether it’s intermittent fasting or something entirely different, I hope you’ll choose to run your own experiments and see what works for you.

The Good & Bad of Intermittent Fasting: Lessons Learned From 2 Years of Experiments [James Clear]

James Clear writes at JamesClear.com, where he uses behaviour science to help you master your habits and improve your health. For useful ideas on improving your mental and physical performance, join his free newsletter, or download his 38-page guide on Transforming Your Habits.


  • This was documented very well recently by Michael Mosley, and if it wasn’t for the conflicting dietary needs of my wife, I would still be on it. There is a lot of evidence that this will prolong life. Unfortunately, it’s very hard to keep up when your wife is a health aficionado and needs to eat a decent meal to keep up her energy, whilst I sit and try not to think about it… 🙂

  • I watched the Micheal Mosley IF show a while ago and even gave it a try (couldn’t handle the mood swings) What i find interesting is the way in which the definition of IF has changed over time. The original scientific study as described in the documentary, was about not eating for 24 hour periods every second day. I spoke to a friend recently about that regime and they informed me that i had it completely wrong and that IF was actually about not eating for 12-16 hours twice a week!!! It really seems to me that the definition of IF has been watered down over the intervening time to make it more appetizing for the masses to the point now that a whole pile of people skip breakfast a couple of times a week (something which has been happening for years since people have been getting busier schedules) and then wondering why they dont get the results that were promised in the documentary. BTW it is my understanding that the evidence of a 75% calorie diet causing longer life has only been proved on mice and not yet humans, and that complications from a continual shortage of energy could counteract the effects (not that many of us suffer from a shortage of energy) I may be behind the times and would be happy for someone to correct me.

    • I’ve fasted upon occasion and you’re right, energy is VERY low, I wasn’t moving fast AT ALL.

      It was quite mentally calming, but I definitely wasn’t a very effective human being. And I had a 6 pack almost, which was nice but i had arms like a little girl. I didn’t look good.

      • Personally, I have always had the opposite reaction. I get incredibly tired when I eat, if I am just having water or juices I am incredibly active by comparison.

        • I get sleepy after a big carby meal but yeah, opposites here. I need food to have energy. Because energy comes from food.

          So dunno what you’re running on. Juices have kj so that makes sense but water alone shouldn’t do much.

          • You aren’t fasting for weeks here heh.. It’s at most days, the most I ever did was 3 days, which was more of an experiment than anything benefit related.

            Besides, the juices and a multivitamin once/twice a day as well as good hydration and a good dose of caffeine do fine. 😛

          • Lol- Nah no way. The most I’ve done is a day.

            I usually eat something with protein in it about 4 times a day. After a workout I have a big carby protein meal. And then I get the sleepies.

            It’s a good life.

    • My only correction would be that they haven’t proved it on mice; they’ve demonstrated it on mice.

      The scientific method is an inductive inquiry and thus can’t be used to ‘prove’ something. This is a ridiculously pedantic point that doesn’t matter to anyone but scientists. When something is conclusively demonstrated in science it basically means the same thing as what lay people mean when they say proof.

      It of course doesn’t stop people from also pretending that because induction can’t prove something, scientific theories are somehow of little value.

      I guess my hope is that if I’m pedantic to enough people, the linguistic issues will diminish.

  • I would like to see this guys numbers. Or pictures. It’s pretty hard to go just on what he reports. Most people won’t do something for 2 years and then write “Yeah, wasn’t really worth it in hindsight”.

    In 2 years, most people who start training can get to some pretty decent numbers. That would be the big tell on how this is affecting his body.

  • ha! my experience exactly.

    My wife and I tried fasting one day a week; still eating on that day (Tuesdays) but drastically reducing calories.

    I found it fine and actually felt really well on those days (though hungry Wed morning) but my wife could not handle it. As she excercises every morning and most lunch times she became much hungrier much faster than I did (plus I have some helpful fat stores I can call upon in such emergency situations) ;).

    I found it pretty hard to continue by myself though with her preparing and eating a full meal next to my steamed cauliflower.

  • Interesting article. At the end of the day whatever works, works – everyone’s body and metabolism operates slightly differently. However I’d probably not recommend this approach as a long term strategy if your only goal is to lose weight.

    From an evolutionary perspective, fasting is akin to starvation, the only obvious difference being that the former is self imposed. Basically when you start to feel hungry in your stomach, you’ve already not eaten for too long. At this stage your body is already trying to lower your extraneous energy output while simultaneously starting to burn fat to provide energy rather than relying on food intake. This initially sounds awesome! – eat less = burn fat. sounds good right? – The problem only arises once you start to eat again.

    The issue is that the digestion process is autonomic; your body can’t differentiate between whether the lack of food is self-imposed or not. So when you start eating again it says to itself, ‘shit, this may be the last meal we get for a while, I should conserve some of this energy for later!’, not knowing that you will definitely be get another meal within 16 hours. So when you start eating again your body converts a much larger percentage of your incoming energy to fat than it would have done had you kept eating through the whole period. It’s the inherent problem with dieting by simply reducing calorific intake, and fasting exacerbates the problem.

    Like I said at the start though, whatever works. I can definitely see the benefit of the simplicity in the mornings, and James you’ve obviously not having the kind of problems I’m referring to. Everyone’s body can learn too, and the less inconsistent and sporadic your approach to fasting is the easier it would likely be for that to happen.

    Personally, I’ve found that the best way for me to lose weight is by getting my metabolism working at a higher resting rate (essentially eating more smaller, healthy, but relatively protein rich meals throughout the day – combined with moderate exercise). Although maybe I just like eating steak a bit too much 🙂

  • I’ve been doing the 24hr style IF twice a week for about 2 years now. I found the first month challenging energy and mood wise, but after that it’s been no problem. I used it as part of my weight loss strategy and suuceded in losing a little over 60 kilos, which I’ve managed to keep off for the last 12 months.

  • I’ve been doing the 24hr style IF twice a week for about 2 years now. I found the first month challenging energy and mood wise, but after that it’s been no problem. I used it as part of my weight loss strategy and succeeded in losing a little over 60 kilos, which I’ve managed to keep off for the last 12 months. But like the author notes, it’s only part of the puzzle, I still had to exercise and clean up my diet. The thing I love most about the IF is that it gave me control over my appitite and cravings – so so important and empowering!!

  • I keep hearing about the mood swings. I do the 5:2 version and never feel anything but energetic on those days so I’m not sure where the mood swings come from. Some other blogger wrote that her kids forced her to eat at 5pm when she started at 9am because of her mood swings……seriously, who can’t go from morning to afternoon without snapping because they haven’t eaten much. I really don’t get this?

    Anyway, I’m on “Mosley” fast day number two of this week. I had toast at 7am with a coffee and haven’t eaten since. I will have dinner at around 7:30pm. I’ve done this for about two months albeit occasionally not that well. I managed to get under my 100Kg plateau which I was on for months and have lost or maintained around 97Kg mark since then. I have not put back on any weight. By not well I mean a few weeks I have only done one day of fasting not two. If I did regular two days I would have been down a bit further. You lose around 400g to 500g per week on two days then switch to one day a week when you reach your ideal weight.

    • It’s usually the low blood sugar that causes the irritability, and some people are much more sensitive to changes in blood sugar than others. You seem to be quite lucky in that regard :).

  • In my opinion fasting is pointless unless you actually change you food habits (in terms of what you eat) and include exercise. It seems to be more of a mind game, making you use your willpower to “control” your urges instead of dealing with them by changing diet / eating habits.

    My belief is that you can achieve the same result but without the fasting.

    • Good belief but in practice majority of people will fail…fasting requires no more will power than simply eating only two meals a day for two days at a reduced intake and you don’t need to motivate yourself hourly, every day to not eat that, do eat this, etc. I find your statement a little idealistic (perhaps a little judgemental as well) for most people especially when today’s style of eating and abundance of food goes against everything our primal brains were designed to do. Will power is finite.

  • There are a lot of ignorant remarks here in the above comments. Nobody appears to understand the science behind it, and why – if done properly, it works. And yes, in conjunction with other healthy habits it works well. Fasting of any kind has well proven benefits, and there are plenty of solid studies that confirm these benefits – but people need to do their own research so that they genuinely understand what they are doing. I’ve been doing the eat 8 hours, fast 16 hours every day since the start of the year, over 10 months. I’ve lost between 8-10 kilos, feel fitter, more energetic, and sleep much better. No mood swings, no negative symptoms at all. It is very easy.

    • My fasting day was last night, I do 5:2, and I was very awake when my wife was tired and wanted to go to bed. This is the downside, I have way more energy now and my wife is very pregnant and those two do not match. I find on fasting days I’m also more focussed at work and study.

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