The Truth About the Fat-Burn Zone

by Jeff Knight
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The Truth About the Fat-Burn Zone

Heart-rate zones are one the best-known yet least understood aspects of exercise. We’ve all encountered them at some point. And in that, you’ve probably noticed inconsistency around names, number of zones and overall information. What you may not know is that there is no governing body of heart-rate zones. Some folks swear there are three zones, some five and others seven. Others argue it’s based on sport — for example, runners get five zones and cyclists get seven. However, there is one heart-rate zone that pretty much everyone knows, especially those of us who frequent the cardio machines at the gym: the fat-burn zone.

What’s not to like about the fat-burn zone? The name alone makes it sound like the ultimate weight-loss hack. And as far as intensity goes, the fat-burn zone falls relatively low on the toughness scale, meaning it’s an easy zone for most of us to hit. Even better news for those of us looking to burn a little belly fat, right?

Unfortunately, that’s not quite how weight loss and fat burning work. To better understand the misconception of the fat-burn zone, we have to look closer at the relationship between body fat and exercise.


To understand how to burn that annoying tummy fat, you must first understand there is more than one type of fat. Among others, there are subcutaneous fat stored under the skin (Think: pesky tummy fat) as well as intramuscular fat stored inside of muscles (Think: marbling in a nice cut of steak). Fat stored under the skin functions as insulation and provides cushioning when we fall (seriously!), but it can build up in excess. Meanwhile, fat stored inside muscle is used for energy. Thus, these two types of fat are used in very different ways.

Unfortunately when it comes to the fat-burn zone, you primarily rely on the fat stored in the muscles, especially for workouts lasting less than one hour. So in reality, that cardio session you thought was melting away those annoying love handles really wasn’t.

Does that mean working out is a waste of time? Certainly not, since exercise burns calories, the driving force behind weight loss. The fat-burn zone may not target belly fat explicitly, but the reality is none of the zones do. So what do we do to get rid of excess fat?


Exercising for fat loss — whether on your belly, back, arms or butt — involves a lot of factors; one of those is burning the optimal amount of calories with each exercise session, not some singular or magical combination of heart-rate zones. A rough rule of thumb is this: The harder you work out, the more calories you burn. For example, a low-intensity 30-minute workout will burn fewer calories than a high-intensity 30-minute workout. Since we all have a finite amount of time we can devote to exercise, in theory we should aim for the hardest zone we can manage every time we exercise. However, this isn’t the best practical approach because working out as hard as possible every day of the week makes us more likely to burn out or get hurt — both of which will work against us in the long run.

A better way to exercise for weight loss is to alternate high-intensity workouts (a 4 or 5 out of 5 on the toughness scale) with more moderate ones (a 2 or 3 out of 5). With this approach, your strategy should be to burn as many calories as possible for the type of workout you’re going for during that exercise period.


At this point you may be asking yourself why we even call it the fat-burn zone if the goal of weight loss (burning fat) is really about calorie burn? Well, because technically you are burning more fat than other fuel sources, like sugar, in the fat-burn zone. It’s just not the type of fat most of us envision melting off.

The Difference Between Burning Fat and Sugar Muscle moves by burning fuel, primarily derived from fat or sugar. Think of these two as a balancing scale. At low exercise intensity, the scale is heavily weighted toward fat, while at high intensity, the scale is heavily weighted toward sugar. There’s a lot more to the story, but, in short, there is only a finite amount of sugar available for energy in your body. As a result, if you’re doing a very long event, you want to exercise at an intensity that maximizes the balance between fat burn and sugar burn. That, in turn, is typically the fat-burn zone.


You know the saying — if something seems too good to be true, it usually is. The fat-burn zone gets a lot of hype but often for the wrong reasons. Thus, it is not the life hack we all wish it were. Keep these three points in mind the next time you hit the gym for a cardio workout:

  1. While exercising in the fat-burn zone (Zone 2) may not directly burn the type of fat you want it to burn, technically your body does burns a lot of fat in this zone. However, overall calorie burn occurs at a slower rate.
  2. If your goal is weight loss, instead of focusing on the fat-burn zone, focus on burning the highest number of calories that’s appropriate for each exercise session, keeping in mind this should be a balance of higher-intensity and lower-intensity workouts.
  3. If you participate in extremely long endurance events, you may benefit from exercising in this zone as a way to preserve fuel and maximize endurance.


  • Matthew Foglia

    so its not true that going from 80% heartrate to 90% heartrate switches between aerobic and anaerobic respiration, which in turn changes the rate at which bodyfat is consumed?

    • Tomickeio Chigbo

      Intensity levels of 50-75% is aerobic and 85-90% is anaerobic. Training at low intensity and high intensity levels will burn fat safely and effectively. Thanks!

      • davedave12

        fat zone might burn fat at a higher rate, but you have to go longer— I bet thin competitive long distance runners rarely run in fat burn zone, maybe one day a week

        it is like walking and running — if you have an hour free to walk 3 miles everyday, great, many people would prefer to run it in 30 minutes

  • When I was training for a marathon, I ate almost all of my calories from fat and achieved nutritional ketosis. My body was using the 20,000+ fat calories it carries around instead if the 2,000 calories of carbohydrates it can maximally store. This allowed me to run 20 miles without any nutritional supplement. I would have been able to complete a marathon without in-race supplement had I not gotten hurt 2 weeks before the race.

    • La Bandita

      You don’t know for sure as you never made it to race day.

      It sounds like you were trying to loose weight instead of win a race. To win a race putting your body into ketosis will get you hurt , mostly spraining or breaking something AND you were hurt. hmmmm

      Your body was probably complaining before you hurt yourself but you ignored. Most likely you would’ve wiped out the day of the race.

      • My injury was not a sprain or break, but a aggravation of an injury I got long before I had LADA or was in ketosis. The week before, I had run 20 miles in 2:40 with no in-run nutrition. “To win a race putting your body into ketosis will get you hurt…” Can you refer me to peer reviewed research that shows that nutritional ketosis is the causal factor for injury in persons training for endurance events such as the marathon?

        • La Bandita

          Yes your ketosis aggregated an injury you already had – we agree. I have done my best runs in practice. Its race day that counts. But I have lots of metals. I ran division one for many years AND had a sponsor, coaches, handlers, dietitians. My issue was that I was so modelly thin at 5 7 living on a high fat diet (Im from islands Spanish and British) and good fats. Fish daily for lunch & dinner. Avacados, mango etc., When my training went into high gear I couldn’t keep weight on. My body went into ketosis. I was switched to a high carb diet but good carbs. I gained muscle, still no fat and was ripped. And began really winning races.

          Ketosis works for body builders, but just for show. If you need to actually use your body for training at a high level you will injury yourself.

  • fromAZ

    If you are restricting carbohydrates in your diet an exercising in a heart rate higher than fat burning zone, you will run out of fuel and likely shift to gluconeogenisis and begin to burn muscle for fuel – not a great idea if you are trying to lose fat. Key point, you better be fueling correctly for high heart rate exercise or you are self-sabotaging.

    • Tazzid Ingram

      Your body will make ketones before gluconeogenesis if you calorie intake is still correct

  • M.Schultz

    I find it frustrating that n My Fitness Pal acknowledges that high intensity workouts are the best for losing weight and YET they do not have that in their cardio exercises so I can track mine! ARE YOU LISTENING MFP? Add HIIT to your cardio exercises so we can track it please!

  • Dave Murphy

    So when you say to alternate the high intensity workouts with moderate workouts…are you saying within the same “workout”? Or one day do a HIIt workout (Cross-fit) and the next day a moderate work out….(swimming or biking)

    • e.Bosselini

      I’m a personal trainer and I do this with my clients all the time. You should alternate exercise intensity during your week of training. I believe the author was suggesting this as well. Remember, you are tearing down muscle tissue during your training and your are repairing that tissue through proper rest and nutrition.

  • Helen Hines

    I am more confused than ever after reading this article! :(((

  • Angela

    This is a horrible article. It doesn’t explain how to calculate your fat burning zone and is incredibly confusing.

  • Sarah Thompson

    Fat loss is made simple and fun with the introduction of blue fat freeze system. It can freeze off any targeted fatty part of the body without lifting a single weight. I used this kit while resting at home and lost 3 inches around my waist in 2 months. But consult your doctor before using it.

  • Janet Esther-Hannah

    I’m more confused

    • Sharon Tarantino

      Me too.

    • davedave12

      The truth is simple, you need 30-40 minutes every other day — if you cannot go 30-40 minutes then you need to slow down. Using the talking test, can you carry an easy conversation while doing cardio, if yes, go faster. Are you gasping for breath, go slower — if you are alone, say your prayers If you can say your prayes one word at a time while doing cardio your speed is about right

      Want to add somthing — do a burst of speed for a minute or twoseveral times during your 30- 40 minutes

      Make things a little harder every two weeks — a bit faster or add longer bursts of speed — after 8 weeks you will be doing more and it will feel easier

  • filmic1

    Because I’m classified as obese, I just make sure I consume fewer calories than my daily allotment, i.e. <2000C/day, and run 3 or 4 times a week, 40 minutes per session. According to my Garmin 320, I'm running always in my aerobic zone, sometimes I allow myself to go into my threshold zone, but carefully. I've improved my VO2max from 28 up to 33 cc/kg/min which is the median for my age group, and I've lost 20lbs so far and have dropped two pant sizes. I still have 50lbs to go, but my clothes tell the truth. I've stopped getting too excited about the theory.

    • Karin Schuster

      i agree. i was so confused by all the science. i log what i eat into an to get an idea of calories consumed to eat less. i also do cardio and strength. why complicated things? KISS

      • davedave12

        all the science is for the margins — I am sure common sense and simple will result in weight loss and complex and scientific will get you 1 or 2 % more weight loss — Tracking my food really helps me be mindful of avoiding junk, getting protein and watching portion size

    • davedave12

      Awesome — if you find you like running and want to improve, you need to go faster from time to time There are lots of training plans o the Internets you can be as complex or simple as you like. In my youth I never ran a mile now in my fifties I run in a March of Dimes 5K every year — going to add a couple more races this year

  • Phillydog

    I am so tired of these so called experts in weight loss. They have the degrees and the government funds all sorts of studies but yet we are fatter than ever. I have a Chinese gf. I was just over there. Very few people are over-weight. Why not just study what they eat and recommend that? Seems pretty simple. Their food is not processed, most is picked and eaten or comes straight from the ocean or farm. Much less meat and WAY more fresh produced is consumed. Very little soda and everything contains fiber. It’s not rocket science. Just emulate their life style and the weight comes off.

    We have all these “fat burning zones”….lol. It’s pathetic, do you think the common Chinese person even works out? Hell no. They just eat right and yes, walk a bit more than us. Skip all the science and emulate the rest of the world and the problem is solved.

    BTW, after I got back I walked in my local grocery store and was embarrassed of all the boxes. My gf is moving here soon, she is in for a culture shock food wise. She is 5’4” and 99 lb and yes, she could stand to ADD a few pounds….lol

  • Maximillian Beckett

    I agree with the comments. This is not a good article. Many other articles say that low carbohydrate diets plus high intensity exercise (zone 4 of 5) equals ketosis and burning fat instead of muscle. I have found that 3 hour hill cycles with no gels/sugar at approx zone 4 don’t lead to muscle loss and to the contrary. Specific and definite pseudo-scientific claims should be supported by footnote references to scientific journals, and to the extent that there is a competing view, should acknowledge that view.