Intermittent Fasting and Exercise: Fat Burn, but Not Necessarily Fat Loss

Read time: 90 seconds

Where is your calorie tank most often?

Most of you who are familiar with and practice intermittent fasting also know that it produces a metabolic and hormonal similarity to exercise.

Intermittent fasting and exercise each increase circulatory catecholamines, growth hormone, and glucagon, leading to an energy metabolism that favors fat burning.

People looking to becoming lean also want the fat burning effect of exercise and intermittent fasting. To be honest, it’s the original reason I adopted intermittent fasting.

But I’ve learned that the true benefit of intermittent fasting is that it allows an energy metabolism that balances calorie storage and usage.

A body that’s not using is a body that’s storing — and becoming overweight. Exercise and intermittent fasting stimulate usage.

But we have to remember that, like gasoline and cars, what our body burns can be replaced at the next meal. Therefore, fat burning does not mean we’ll lose fat off our stomach and thighs, if we consume more food than we need.

So why even do intermittent fasting?

Well, aside from supporting a balanced energy metabolism, intermittent fasting helps us learn how to eat less without feeling deprived.

When the stomach is empty after a certain period of time (say, 4 hours of fasting), it rebounds back to a certain unfed size. And because this rebound isn’t linear with time, it achieves the same size whether we’ve fasted 4 hours or 18.

Thus, any (somatic) hunger in our stomach at hour 18 is of the same magnitude as that of hour 4. Psychological hunger, however, may be at a different magnitude, but this can change through the natural re-conditioning that occurs with daily intermittent fasting.

The re-conditioning of psychological hunger is the main factor in making daily intermittent fasting successful.

But, as in most cases, there’s a mind-body connection, and the re-conditioning of both somatic and psychological hunger is based on the releasing pattern of ghrelin, the hunger hormone. When we eat fewer times, ghrelin is released fewer times, and as a result we get hungry fewer times.

Intermittent fasting, like exercise, can burn fat, but alone it doesn’t necessarily cause fat loss. We have to be careful not to put back in more than we burn. But intermittent fasting makes it easier for us to put back in less.

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9 Responses to Intermittent Fasting and Exercise: Fat Burn, but Not Necessarily Fat Loss

  1. Nicole R says:

    Great message, Johnny. Sometimes we can oversimplify a simple concept. I had thought that the enhanced fat burning from IF was enough, but your message is clear that we can easily reverse it with overeating. I think some people are really stuck on a single concept (fat burning from IF, low-carb, Paleo diet, etc), and defend it to the exclusion of other factors. Thanks for another great post!

  2. Al says:

    IFing is the most powerful tool to get lean if one does not gorge on a daily basis.

    Through my experimentation when someone takes their basic meals (3,4,5, whatever) and shoves them into a feeding window without gorging than IFing can be your best friend.

    The funny thing with IFing is that those old basic meals tend to be reduced when implementing IF. Awesome stuff.

  3. MIchmich says:

    HI Johnny,
    Thanks for such a great blog.. I love your site and read it daily.. I have started IF all day and find it to be very liberating as you say.. I also have noticed that as I slow down when I eat and concentrate on enjoying each bit the length of my meal is extended giving time to by body to signal to my mind that I’m actually no longer hungry – and my food consumption decreasing naturally as I become more in tune with my body signals.
    I have been eating primal / paleo for a couple of months now however I have not seen a change at all in my weight like many others have.. I have 25 lbs to loose and wondered how long it takes, generally of course as I know that everyone is different , to start seeing results based on your experience? I am at a point where I need some encouragement I think and maybe some guidance on how to tweek my diet/ exercise routine to really kickstart this leaning out process..
    I think you look really incredible – and as you mentioned in one of your latest posts your wife has leaned out as well with the introduction of IF into her lifestyle.. I am female in my mid forties and fairly active – used to run a lot but due to an IT band issue had to stop last year and I’m trying to find the right exercise fit for me – I do weights and get out walking to stay active however I’d like to really ramp up my routine and start seeing progress .. Slow and steady but at least.. something ! :-)..
    thanks for any help or advice you can share ..

    thanks !

  4. KellyD says:

    Hi Johnny,

    I’m loving your blog. I found it while searching for “intermittent fasting blogs.” I started eating one meal a day three days ago. I’m a 52 year old female, martial artist, but also overweight. I overdid the one meal last night – I felt stuffed. Anyway, I ate at 6:15 pm last night. It’s 1:33 pm now and I am still on fire. I was hot all night last night and feel like I’m still flushing. In fact, my body temp is up. I assume that my metabolism has increased between eating a larger meal and fat burning? Has anyone else experienced this?

    • Johnny says:

      Hi Kelly,

      Only on rare occasions do I feel the thermic effect of eating a meal, but never long after that meal.

      Although short-term fasting increases fat metabolism, it doesn’t necessarily mean the metabolism increases significantly. Whereas the body burns more fat during IF, it also burns less glucose, and therefore the difference in heat output might be insignificant.

      Keep an eye on the temperature you’re feeling — it could be a symptom of something else.

      I encourage you to keep with your one-meal-a-day for a while. Even if you overeat at that meal, it’s most likely still fewer calories than if you were to eat several meals all day — not to mention the greater fat metabolism of short-term fasting.


  5. Jordan D. says:

    I’ve also experienced feeling overheated after eating a big meal. Yet another reason not to overeat! It’s not fun waking up in the middle of the night, drenched in sweat.

  6. KellyD says:

    Hi Johnny and Jordan,

    Thanks for the replies.

    One thing that could be contributing to the overheating is that I’m in NY and we don’t have a/c. It’s supposed to be near 90 today and the humidity is up.

    I have been so hot, I’ve had a problem sleeping. I keep waking up. It could be female hormones but I don’t think so. I haven’t gone through menopause yet. Some women do have a slow roast instead of hot flashes though. Also, when estrogen drops, we can become testosterone-dominant which could explain the heating up. I really suspect eating large meals however.

    As far as the calories go, I’m definitely eating less. I’m eating at 40% to 50% less. My meals are about 1100 – 1300 calories. That isn’t hard to do if you throw in some good fats. However, I’ve been overeating by eating dessert. If you are full, you think you have room for dessert but you really don’t! I’m sure that once I hit all the foods I’ve been deprived of I’ll stop overeating.

    I’m 5’3-1/2″ so 2200-2500 calories was way too much. One problem is that exercise increases my appetite. Minimeals sure didn’t work. All those did was train my body to be hungry all the time. How unnatural is that?

    My only concern is that when I cut dessert, I may be left with 800-1000 calories a day…unless my appetite increases after significant fat loss. I realize that the gut becomes very efficient at extracting nutrients though.

    What do you all think about 800-1000 calories during the weight loss phase. I’m thinking of cutting dessert because it’s just too much food. If I up the calories that may mean stuffing myself.

    Do you think that once the excess fat is gone that my body will demand more food?

    • Johnny says:

      Hi Kelly,

      Nothing wrong with eating 800-1000 calories a day for a stretch. It’s very effective for weight loss. After you’ve lost the weight you want to lose, you can switch to eating your maintenance calorie level. You’d have to figure out what that is, and the simplest way is to add back a few hundred calories at a time, and see how your body responds. Just remember that when you’re lighter, your daily calorie requirement is also lower; so don’t over-shoot when you switch to maintenance.

      Despite what many people will try to tell you about eating 800-1000 calories per day (harmful, bad for your metabolism, yadda yadda), it is perfectly fine for a period in which you’re trying to lose weight/fat. Just make sure you include resistance exercise to maintain muscle mass.

      Two studies show subjects on 800 calories per day for a 3 months can build muscle mass, and experience no ill health effect (Donnelly, 1993; Bryner, 1999).

      Don’t let the neo-experts spew the same-old recycled warning that extremely low calorie intake is bad for you. Used temporarily, it has been proven to be very effective for weight loss and concurrently safe. At completion of weight loss, switch to maintenance intake — which is lower than the level that caused the weight gain in the first place.


  7. KellyD says:

    Thanks a million, Johnny.

    That’s very encouraging that two studies showed that one could actually build muscle mass on 800 calories a day and also not experience any ill effects.

    I’m going to go ahead and cut out the desserts. Desserts just stuff me and that can’t be good. Well, a small piece of chocolate or something like that would probably be just fine and just as satisfying.

    Today, I ate at 3:30 pm. It’s 10:53 pm and I’m still full. I love this way of eating.

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