The Fat Burning Zone Myth: Don’t Be Fooled

  • Print Friendly and PDFPrint

fat-burning-zone-myth

The fat burning zone is one of the most pervasive myths in the fitness industry that just won’t go away. Magazines constantly promote workouts in the fat burning zone as an effective way to burn fat and most cardio machines around the world have some type of sticker, or image clearly visible (see image to your right).

The idea is if you keep your heart rate in the “fat burning zone,” which is roughly 55% to 65% of your max heart rate, then you will magically burn more fat than at higher levels of exercise intensity.

Why work harder, when you can take it easy and burn more fat, right?

Well this, my friends, is why the fat burning zone myth is so attractive. The truth is at best, the fat burning zone is very misleading, and at worst, it’s complete misinformation.

This article will teach you 2 specific reasons why the fat burning zone is a myth so you can workout to optimally burn fat.

The Fat Burning Zone Confuses Absolute vs. Relative Fat Burn

To understand the fat burning zone myth, you need to understand how your body uses energy during exercise. To keep things simple, during exercise your body draws energy from primarily two places: fat stores, or glycogen stores. Glycogen is stored carbohydrates in your muscles and liver.

The fat burning zone was conceived because at lower exercise intensities more fat is burned relative to glycogen. Isn’t this awesome? Now you can hang out on the couch and lose a bunch of fat. I hope you are starting to smell something fishy with this idea of a fat burning zone.

At 50% of your max heart rate, your body burns a ratio of 60% fat to 40% glycogen. At 75% of your max heart rate, the ratio is 35% to 65%, and at even higher intensities, the ratio is even lower.1

So why the heck would you want to workout so hard if you burn so little fat?

The reason why is because it’s all about calories. You burn a lot more calories when you workout intensely than you do when you are sitting on the couch.

So here’s what the breakdown looks like assuming 30 minutes of exercise for a low vs. high intensity group. The high intensity group will likely burn double the calories as the lower intensity group, or 200 vs. 400 calories:

30 Minutes of Exercise Fat Calories Burned Glycogen Calories Burned Total Calories Burned
Low Intensity Group (50%) 120 80 200
High Intensity Group (75%) 140 260 400

So now you can see you burn more fat calories at a higher exercise intensity than a lower exercise intensity (140 vs. 120) despite a smaller percentage of fat being burned. But I know you need more convincing because the higher intensity exercise represents only a 20% difference in fat calories burned for a 50% increase in intensity. Not a good tradeoff.

There is something important we are missing in these calculations, which you will learn in the next section.

The Fat Burning Zone Has No Afterburn Effect

When you exercise at low exercise intensities, you burn very few calories after the exercise is completed. When you exercise intensely such as during a HIIT workout, there is a metabolic disturbance that burns calories after the workout is completed. This is known as the afterburn effect.

Estimates of the afterburn effect vary wildly depending on the exercise method, the intensity of the workout, and even how its measured.

In a study by Dr. Christopher Scott and the University of Southern Maine, the total calorie burn of low intensity exercise vs. high intensity exercise was examined. A low intensity exercise group cycled at a steady rate of 3.5 minutes. The higher intensity exercise group required three 15 second sprints as fast as the subjects could run.

What was the difference in calorie burn? Quite substantial.

The cycling group burned 29 calories vs. 4 calories for the sprinting group during the exercise. But when you take into account the calories burned after exercise, or the afterburn effect, the numbers look much different – 39 calories burned for the cycling group vs. 65 calories burned for the sprinting group. A surprising 95% of the total calorie burn occurred after the sprinting exercise!2 Keep in mind the cycling group exercised for almost 5x longer than the sprint group (3.5 minutes vs. 45 seconds).

If this isn’t enough convincing, one study showed a significant amount of fat was broken down from fat stores in the muscle following high intensity cycling sprints.3 During high intensity exercise, you are burning primarily glucose, but after is when you burn the fat. This is the crux of the fat burning zone myth and the afterburn effect.

While low intensity exercise certainly has its place within an exercise regimen, relying on exercise in the fat burning zone to burn fat is not an efficient approach. Contrary to popular belief, getting up early in the morning to do low intensity cardio on an empty stomach will not help you lose more body fat versus other more intense methods. For busy people, interval training and circuit training workouts are substantially more efficient to help you burn far more calories in much less time, and burn more fat in the process.

With all that said, I highly recommend not relying on exercise to “burn fat” to get lean. In the context of a fat loss program, exercise helps you keep your muscle, stay fit, make modest increases to your metabolism, and burn some fat. Because it’s a scientific fact that you must eat less calories than you burn to lose fat, nutrition has a much more powerful impact on this equation and consequently, it should be your main focus.

References

  1. Source: Bryant, Cedric X. 101 Frequently Asked Questions about “Health & Fitness” and “Nutrition & Weight Control“. Sagamore Publishing, 1999.
  2. Scott, Christopher. “Misconceptions about Aerobic and Anaerobic Energy Expenditure.“Journal of the International Society of Sports Nutrition 2.2 (2005): 32. BioMed Central. Web.
  3. 3. Available at: http://www.builtlean.com/2011/06/29/afterburn-effect-of-exercise-qa-with-dr-christopher-scott-phd/. Accessed March 14, 2013.
Medically reviewed by Michael Ryan
GD Star Rating
a WordPress rating system
The Fat Burning Zone Myth: Don't Be Fooled, 4.5 out of 5 based on 346 ratings

30 Comments on “The Fat Burning Zone Myth: Don’t Be Fooled

  1. Steve Brown
    April 1, 2013 #

    How/where exactly does low intensity exercises fit an exercise routine? I loathe cardio so I do it all as HIIT & I rest as little as possible when strength training. Maybe yoga? But even in that I do quick flow Vinyasa which can be intense

  2. ken
    April 1, 2013 #

    great article! I always see people walking on the treadmill at some steep inclines…somebody should tell them, its all about the HIIT!

  3. John
    April 1, 2013 #

    True…but you can do low intensity for hours and burn a lot of calories if you’ve got the time.

    You can also do it every day without concern, if I walked an hour every morning before breakfast that would burn a lot of calories over a month.

  4. uncadonego
    April 2, 2013 #

    Yes, sure John, if I’m watching the latest episode of Castle like last night, I’m sitting anyway…might as well pedal. So sure, burning calories low intensity is OK, but in addition to…not in lieu of the real workouts.

  5. Sree
    April 2, 2013 #

    HIIT is promoted as being one of the most effective cardio-based workouts for fat loss. At the end of an HIIT session, I see that I burn about 25-30% more calories than a normal cardio workout but I feel more than 2X tired. Is this the way fat loss is supposed to work?

    1. April 2, 2013 #

      @Sree – Fat loss works by eating less calories than you burn. HIIT can assist with this by helping you burn more calories in a shorter period of time and helping increase your metabolism post workout. The fact you feel 2x more tired is because the workout is more intense.

  6. Ken_K
    April 3, 2013 #

    I was quite lean one year from doing a lot of walking and having less than enough sleep. Except for the walking to and from work, I hardly did any exercises. So it is possible (for me) to do low intensity exercises and lose weight. Now, I do at least 2 interval style of at least 15-minute workouts a day, seven days a week, and I still don’t look as lean as when I was then. On the positive side, the 14 mini-workouts per week lowers my stress level.

    1. April 5, 2013 #

      @Ken_K – Absolutely you can do low intensity exercise and lose body fat. The point of this article was to dispel the myth that low intensity cardio is optimal for fat loss, which I don’t agree with. At the end of the day, any exercise is going to help you burn incrementally more calories than if you weren’t exercising, which will certainly help. I also wrote an article about 30+ reasons to exercise in addition to body fat loss => 31 Reasons To Get In Shape & Exercise. Good luck!

  7. uncadonego
    April 3, 2013 #

    Ha! Ha! I used to worry about getting huffy and puffy and tired…..until I realized that was the point!!!

  8. zorba74
    April 4, 2013 #

    A lot of of people take up exercise not necessarily to get lean. One of the benefits of regular moderate intensity cardio ( 20-30 minutes of high heart rate exercise at least 3 times per day) is supposed to be a reduction in the risk of coronary artery heart disease and also prevent hypertension, metabolic syndrome etc. I think this effect is independent of the effect of cardio on fat loss .

    Would the cardioprotective benefits be the same for moderate cardio, high intensity cardio and HIIT ? Any studies which provide a clear answer? Thanks

    1. April 5, 2013 #

      @zorba – there are a lot of studies that show the benefits of HIIT from both a cardiovascular improvement and fat burning perspective.

      I have HIIT references at the end of these two articles:

      1) High Intensity Interval Training (HIIT): Best Cardio to Burn Fat

      2) Get Cardiovascular Benefits Without Doing Cardio? Here’s How…

      Hope that’s helpful!

  9. ED
    April 5, 2013 #

    I am eating a nice fresh apple as I read this :)

  10. Daniel
    April 5, 2013 #

    Yet Another helpful article Marc, you seem to have answered almost every question there is in fitness

    1. April 5, 2013 #

      @Dan – Thanks a lot, Dan!

  11. Mike DiCarlo
    April 5, 2013 #

    great article as always Marc! i agree with what you say and from my personal weight loss experience i think that the “fat burning zone” is, or should be, geared more towards people with a lot to lose. when i started working out i would do low intensity cardio for long periods of time, usually at least an hour, hour and a half, six to seven days a week and it worked, i lost 2, 3, 4 pounds or more per week but i also ate a lot less than i ever had before so i would end up with big calorie deficits at the end of the day. the age old calories in, calories out does work for fat loss, and for larger people, the lower intensity is safer. exercise is rough on bones and joints when youre 100 or 150+ lbs overweight and also you dont usually have a very good muscular structure or the balance to support HIIT at that time so i think thats where the low intensity has its place to get a person accustomed to working out and conditioned to be able to handle higher intensity exercise down the road. oh, and i also think you really hit the nail on the head in your last sentence, diet really is as important, more important really than anything when youre just looking to lose fat. i really see that now that i weigh so much less and i have less to lose. when im not on with my diet, i dont lose no matter how hard i work. it sucks, but you really cant outwork a bad diet!

    1. April 5, 2013 #

      Thanks for sharing Mike!

  12. Daniel
    April 6, 2013 #

    Thank you for this article Marc.
    Your writing always make a clear difference between all what’s posted on the internet.

    Furthermore, it correlates and bring answers to my personal research

    It’s been 8 months now that I tested various Hiit methods and grabbed data with a cardiofrequence meter.
    What I discovered that was pretty well working for me is the following:
    Subject : male – 47y.o – 1.63m – 63kgs – 9%bf
    engine : elliptic
    routine:
    180sec warmup low intensity (level 3 on elliptic)
    9 x 24sec highest possible intensity (level 20 to 25 max on elliptic)
    9 x 36sec low to no intensity (level 3)
    180sec cooldown low intensity (between level 5 and 10 due to hiit stress)

    this makes a 15mins Hiit routine allowing me to burn 300+Kcal
    Concerning heart rate:
    at warmup : around 65% of max, mine being 173bpm (220-age)
    during Hiit : between 75 and 95%
    at cooldown : from 90% to 65%

    Very long and efficient EPOC, I could feel I was kinda breatless for hours after the workout.

    Using low intensity I achieved the same result in about one hour (static bike) but then no EPOC at all.

    Daniel

  13. zorba74
    April 6, 2013 #

    Thanks for the references Marc. By the way, when I say cardiovascular improvement, I didnt necessarily mean improvement in heart/cardiac muscle and function- what I was looking was demonstrable improvement in the rates of atherosclerosis and coronary artery disease.

  14. Kristin
    April 6, 2013 #

    @Mark: In your chart, heart rate zones over 85% are considered in the ‘danger zone.’ How does that fit in with doing HIIT? I can get my heart rate up to 182-184 (Which is over 100% according to the max heart rate calculators ;b) and always do when doing HIIT. A few times I got it up to 194! I thought it was an error the first time, but it happened a second time and both times I was so tired afterward I slept for the rest of the day.

    On a search I saw you can damage your heart doing HIIT but I was not able to find out much in the way of details. I assume this is true? Or does the body protect itself? Another site commented that it is hard to know one’s true max heart rate as it is really hard to get your heart to max out, and the estimates are broad estimates. (yep the devils is in those darn details :) ) So, as the charts are just an estimate, how hard should you push yourself? I wonder if going to 182 is too high, but I have never suffer any repercussions.
    Also, thanks again for another great article!

    1. April 7, 2013 #

      Hey Kristin, I think the “danger zone” should probably be a separate article! I think intensity really depends on fitness level and age. For someone who is fit and athletic, 95% of max heart rate is what is expected in a tough workout. 85% of max heart rate is definitely NOT the danger zone for someone who is in good shape. For someone who hasn’t exercised in a few months in their 70’s, 85% of max heart rate may cause nausea etc. and is likely dangerous. I wrote an article about max heart rate and how it can be highly variable => How to Calculate Max Heart Rate?. In my opinion, if you are concerned about your workout intensity, I would wear a heart rate monitor and cross reference how you feel with your heart rate. Also consider as you get in better shape, it will be harder to maintain a higher heart rate.

      1. Phil
        April 13, 2013 #

        Hi Mark. I am new to workouts, started them a couple of months ago. Before starting, I made a meticulous research on how to do it and methods in more than a hundred sites (I am not exagerating), papers, and other sources. I am on my 50s, lots of work, no time to lose with unnefective techniques. I can tell you that your site and your propositions, methods are the most logic I ever found. They really are bringing me results. I subscribe to your site with another one as the basis for information for my workout programs. Thank you for that. I do not want to get out of the subject of this article, but by reading your comment above on the nausea feeling. I used to practice karate when a teenager. I remember having strong nauseas at that time when doing the aerobic exercises. As I grew older, nausea reduced and since 10 years ago disappeared no matter how much I do aerobic exercise, including HIIT. Is that something I should check? Thank you for your advice.

      2. April 13, 2013 #

        @Phil – Sounds like you are in better shape, you are more properly fed/hydrated before you workout, or maybe as you aged you became more accustomed to exercise. Any way you slice it, it’s a positive thing that you are not getting nauseous, so I don’t think there is anything to get checked out. Thanks for the kind words regarding the site and happy to hear you are doing well with the workouts!

      3. Kristin
        April 13, 2013 #

        Ha! I gave you a new topic to write on ;b
        The Max Heart Rate article slipped under my radar. Sweet, statistics/standard deviations! Thanks!!! That explains everything, and I think I am good for my high end zone.
        I do wear a HR monitor (which is why I knew where I was at) and I know my HR tends to run a bit high anyhow (I think I am one of those high beaters?). I’ve been working out for many moons now though, so I don’t think I will see a huge improvement over where I am at. I had my V02max and lactic threshold tested not too long ago. Doc said I could improve on the lactic threshold a bit but but the VO2max looked fine. Hey, there is another article topic. Can’t say I fully grasp VO2max & lactate threshold, but I was getting some other tests done and they weren’t that much more to add on.

      4. April 13, 2013 #

        @kristin – sounds like a plan. Will consider a VO2Max/Lactate Threshold article, but it may be too technical for most readers!

  15. April 9, 2013 #

    Excellent article. There is no doubt that your method works well.

  16. April 9, 2013 #

    I thoroughly enjoyed both this and the “Best Hit Treadmill Workout” article. Quick question though, Is there a substantial difference between using say an elliptical vs. a treadmill? I have very bad knees is why I ask this and 5 days a week running leaves me in serious pain.

    1. Kristin
      April 13, 2013 #

      Hi Ben (sorry I’m not Mark) but the elliptical is not as high impact as running, which is why it is not as hard on your knees. Personally, I’d stick with what does not cause you pain (your knees are probably telling you something). As long as your heart rate is getting up to where it should be on the elliptical, your cardio system isn’t going to know the difference. You should be doing something like weights though to counter not doing high impact cardio to keep your bones strong. Alternatively, you can crosstrain, like doing elliptical one day and running the next. I can only run so much myself due to a foot injury, so I intermix my running with biking :)

  17. jeff
    April 17, 2013 #

    Thanks for the “advice”, i love to walk for hours, so now if i go do it everyday i will feel like I’m doing good for myself and maybe see some results.

  18. April 30, 2013 #

    I used to be down on extended periods of strolling for exercise, but I have come to realized that one of its most underrated functions is to get people in the worst shape out of the house and away from easy snacking when they are most bored. I now recommend it as a “gateway” exercise.

  19. uncadonego
    April 30, 2013 #

    Agreed Katherine, going for a walk is definitely a good way to curb the desire to mindlessly snack and get your body moving. :-)

Comments are closed.