Is The Fat-Burning Zone a Fitness Myth?

Posted on Apr 11th 2011 12:00PM by That's Fit Editors

Filed Under: Fitness

Getty Images

Provided by Well and Good NYC

It's cold outside. And as the temperature dips, many New Yorkers head indoors to work out, trading the soupy city streets for a treadmill or stationary bike. And that's where many of us encounter a puzzling (and often dated-looking) diagram pointing out the so-called "fat-burning zone."

The reason it's plastered all over the gym? Proponents of the zone argue that it represents a kind of exercise sweet spot-typically between 60 and 70 percent of our maximum heart rate-in which our bodies burn the most fat.

So should we buy into the idea?

In a word-no.

On average, when we're resting, 60 percent of the energy we use for fuel comes from fat, 35 percent comes from carbohydrates, and the remaining five percent comes from protein. But when we exercise, our bodies begin burning more carbohydrates to fuel our activity, and less fat. All of which has led some to argue that we should work out at lower intensities to trick our bodies into using more fat as fuel.

Feel free to watch TV at the gym: This popular chart may not be worth your time and attention

Unfortunately, that's not true.

"The practical way most people think about the fat-burning zone is that they're using more fat to fuel their exercise and therefore, they're going to lose more body fat," says Dr. Karen Reznik Dolins, a professor of nutrition and physical education at Columbia University. "That's incorrect. The amount of fat you're going to lose is totally dependent on expending more calories than you take in."

In other words, the problem is that as you decrease the intensity of your workout, you also decrease the overall number of calories you burn.

What matters most when it comes to exercise and weight loss is using as many calories as possible, so that at the end of the day, you've expended more than what you've consumed. According to Dr. Reznik Dolins, most people are likely to achieve this goal by exercising as strenuously as possible. (Hey, we don't mind a few intervals.)

The bottom line? The idea that there's some kind of magic zone whereby you exercise less intensely, don't increase the length of your workout, and somehow burn more fat is, sadly, false. -Catherine Pearson

Around the Web

Reader Comments (Page 1 of 1)

Lia 4-13-2011 @ 6:03AM

There is an extremely informative free video on this web site ( Http://bit.ly/RealSmartWeightLoss ) that reveals the simple proven science of weight loss that no one else will tell you about so that you will lose weight in a steady, healthy and permanent way. There are literally thousands of weight loss systems, pills, supplements and guides on the market that don't work. This proven system is the real deal and changes everything.

Darvis Simms 4-12-2011 @ 1:06PM

As a fitness professional I try to educate people on the best ways to improve their fitness level. I try to have my clients to understand that about 75 percent of the exercise they have to do to lose weight is with a knife and fork. Too often people get caught-up in which exercise burns the most fat when their eating habits are horrible. No amount of exercise of any kind can compensate for poor eating habits.

fran 4-12-2011 @ 11:46PM

many vitamin fanchises like GNC are going under due to their overpriced vitamins and douche bag employees. i've been buying GNC vitamins since the 60's on Coral Way in Miracle Mile Coral Gables Florida. bUT LIKE MOST CRAP GNC IS OVERPRICED AND OVERRATED, IT JUST AS GOOD AT WALMART, CVS OR WALGREENS FOR A FRADCTION OF THE PRICE

lisa 4-13-2011 @ 5:19AM

and you felt the need to get on a fat burning article and bash a health store and call women that YOU don't even know douche bags WHY? The only one looking like a douche bag at this moment it you.

ryan 4-13-2011 @ 11:07AM

I think that this article is totally wrong. I have worked as an athletic trainer and personal trainer for over 17 years. I have two Bachelor's Degrees, one in Kinesiology, and on in Physical Education. I have studied exercise physiology in depth. When I first started studying it made total sense to me that it was calories in versus calories out. And you know what, when it comes down to it, it is calories in versus calories out. However, it isn't as simple as it sounds. Things we don't realize we do aside from exercise effect our calories out. For example, eating frequency. For example, if you eat 3000 calories a day, and you eat it all at once, it's not the same as if you eat 3000 calories a day and split it up into 5 or 6 meals. That's why almost any dietitian, trainer, or doctor that understands what they are teaching will tell you to eat small frequent meals throughout the day. Basically, each time you eat, it takes calories to break down your food and elevates your metabolism. Also, if you eat a small meal, your body will use that food for energy for the next few hours and won't have enough to store any fat. Another factor that is important to consider is in order to burn fat efficiently your body needs to have blood sugar present from food that you have eaten the past few hours. When your body runs out of blood sugar from the food you have eaten, your metabolism goes into starvation mode. In starvation mode, your body conserves energy. Fat is stored energy, and since your body senses a lack of energy present from food intake, it tries to hold on to fat stores and burns them at a lower rate than normal. In doing this, your body still needs to provide energy to perform it's tasks. But since it doesn't have carbohydrates from foods recently eaten and fat breakdown is inhibited while in starvation mode, protein from your muscle tissue is broken down to provide your body with energy. This lowers your overall resting metabolic rate (RMR) because your RMR is directly related to your muscle mass. The more muscle mass you have, the higher your metabolism. A good analogy I like to use is your body is like an engine. A larger engine, like a truck, burns more fuel than a smaller engine like a scooter. When you starve your system, you make your engine smaller. Also, when you eat large meals, your body is provided with more energy than it needs over the next few hours. It senses that it has more energy than it needs for now, so uses what it needs for the next 3-4 hours and stores the rest. Unfortunately stored energy=fat. So it's a double negative. Anyways, I know this isn't what the article was talking about, but if you've gotten this far, I will address that issue as well. The reason I brought up this in regards to the article was because the doctor in the article said it's as simple as calories in versus calories out. It's true, but if you don't understand it is a little bit more complicated than that, a person will think eating 3000 calories all at once or spread out throughout the day is exactly the same thing. Now in regards to the fat burning zone, I believe there is a fat burning zone. Basically, as the article says, at rest we burn 60% of our calories from fat. This is very true. But I don't think she addresses or understands why it is that we burn 60% at rest. The reason we burn fat as our primary fuel source is because we have oxygen present. When oxygen is present, we are in aerobic metabolism. In aerobic metabolism, the primary fuel source for our activity is fat. At rest, however, it doesn't do us much benefit, because we don't burn many calories. The key here to understand why they say the fat burning zone is 60-70% of your maximal heart rate (MHR) is that above 70% of your MHR, your body starts going into anaerobic metabolism. This means you are not giving your body sufficient oxygen to get energy by it's normal means. Your body adapts to this situation using carbohydrate is its primary fuel source rather than fat. In order for fat to be a primary fuel source, you need to have oxygen and blood sugar from food eaten in the past 3-4 hours present. The way I personally do it, is if I have eaten a large meal the 2-3 hours prior to a workout, I do an anaerobic workout. My logic is I have a lot of carbohydrate present, so if I don't immediately burn it off, the excess is going to get stored as fat. If I ate a small meal 2-3 hours prior to a workout, I do more of an aerobic workout. The logic is that I have eaten enough food to give me energy for my workout, but not so much that any will get stored as fat. And since I am doing an aerobic exercise, 60% of the calories will come from my fat stores. The doctor who wrote the article is right when she says the more intense the workout, the more total calories are burned. But you want to burn the proper calories. And you want to be at 60-70% of your Maximal Heart Rate rather than lower because you are burning the maximum amount of calories you can in the aerobic mode, meaning that you can use fat as your primary fuel source. Also, when you are in the aerobic mode, you can go for longer periods of time, because you don't get winded. When you go into anaerobic metabolism, you run out of breath and need to stop a lot quicker. So even though you burn more calories in anaerobic mode, you can't sustain it for as long and you aren't burning fat as efficiently. Hope that makes sense! It's so frustrating that some doctor, who probably is a general doctor and doesn't focus on exercise physiology thinks they know everything about everything just because they are a doctor. If I have learned anything in my studies of the human body and my experiences in life, I have learned that we need to be educated and use the doctors as knowledge as general guidelines, but we need to do our own research because many of the times they don't take the time to know all the details of every part of the body. And I'm not criticizing them for that, because there isn't enough time in the world for them to be specialists at everything. My point is, just because a doctor says something, don't necessarily believe it is true. Do your own research if it is an important topic in your life. In the end, nobody knows your body as well as you do, and if you educate yourself in certain areas you will find that you can find out the answers better with your input in conjunction with the expertise of a doctor. When you present facts in an intelligent manner to a good doctor, it will help them figure out what may be wrong with your health. In today's world, doctors don't have that much time to spend on each individual. Like I said before, it's not their fault, it's just the system forces them to be in a position to move from one patient to another without putting a lot of thought into each patient sometimes. Peace and I hope I was able to help.

John Blakely 4-13-2011 @ 11:28AM

Good information but the way the body burns fat and carbs is never one or the other but different amounts of each. This isn't able to be known but someone who just signed up for a gym membership. In fact it is difficult even for those with very good analytical lab equipment. DNA is also a big player. If you want to know how you will add and burn fat, look at your parents.

I liked your information on the doctors too. They are the perfect people to go to when you're experiencing illness or injury but often not so good when health, strength and endurance come to the fore.

jj 4-15-2011 @ 3:49PM

Look at me! Look at me! Look at me everyone!

patrick 4-15-2011 @ 4:17PM

I agree with "ryan" that this article is wrong. I don't have his credentials, nor am I a physician, but I have been exercising for a long time and I do watch my heart rate. As "ryan" has correctly stated:

"..when you are in the aerobic mode, you can go for longer periods of time, because you don't get winded. When you go into anaerobic metabolism, you run out of breath and need to stop a lot quicker. So even though you burn more calories in anaerobic mode, you can't sustain it for as long and you aren't burning fat as efficiently"

And I also have noted that most physicians have book learning on this subject only and have not really applied it themselves with success over a long period of time. Like so many other fields today, Medicine is much too broad for one person to "know it all" so physicians have to defer to the exercise physiologists and other experts who have (preferably) themselves done what they are recommending ...or at least done it successfully on many trainees.

The article correctly states that the key is to "expend more calories than you take in." But what the author misses is that only practical long-term way to increase caloric expenditure is in the aerobic range; the anaerobic range is not a practical option, not only for the reasons "ryan" has stated but also because it increases exhaustion causing the most subjects to decrease their exercise over time. Individuals become less productive in their professional/personal lives and/or start to skip exercise for long periods of time due to exhaustion.

Bob K 4-13-2011 @ 9:28AM

The article doesn't really explain the issue fully, although it is correct. A further explanation is:
the more intense the workout, the greater the number of calories burned, although a lower percentage from fat.
So, at rest, you burn 100% fat, but maybe 10 calories of fat. However, when operating at 80% of max cardiac output, you burn a lot of carbs, protein, and fat. So if you burn 400 calories in an hour, perhaps only 25% come from fat, but that's 100 calories. Better than 10.

ryan 4-13-2011 @ 11:25AM

yes, but the comparison shouldn't be the calories you burn at rest to calories you burn at 80% of maximal heart rate. The comparison should be the amount of calories you burn at 70% of maximal heart rate to the calories you burn at 80% of maximal heart rate. Yes you're going to burn a few more calories at 80% than 70%. But the key is only slightly more calories at 80% than 70%. Plus, it won't be as many fat calories. And another key is at 80% of your maximal heart rate, you will get out of breath because it is anaerobic, meaning the energy demands exceed the amount of oxygen your body is getting, and you will not be able to sustain it very long. If you go at 70% you are still in the aerobic metabolism, meaning you can do it for a longer period of time, your primary fuel source is fat, and over the course of your workout you can burn just as many calories because you can maintain your heart rate at 70% the whole time. You can maintain your maximal heart rate at 70% easily for an entire hour, but you can't maintain it at 80% for an hour.

John Blakely 4-13-2011 @ 11:26AM

Everyone in this country wants the easy way to "look" really fit. They really don't care if they are fit, they want to look fit. That's why sports were so loaded up with steroids and HGH, they did a lot of work but wanted it to be less painful with stronger results.

People hate to count calories but unless you have access to the analytical lab equipment necessary to measure your fat, carb, and protein usage, it is your best bet. You want to eat a lot of junk and then go walk on a treadmill thinking you're a fitness freak? Dream on. If you really want to be fit or even just look fit, the easiest road is the honest road. Eat a balanced diet as is recommended by the USDA (they have a terrific on-line web site), workout with cardio exercises and resistance exercises. Make it a part of your personal routine and you'll feel great and look good too.

Also, don't get too hung up on getting motivation. The best motivation that anyone can obtain and keep in motion is good personal discipline.

doubtit 4-13-2011 @ 11:25AM

sources? otherwise this is all conjecture

ryan 4-13-2011 @ 11:32AM

Also, you don't burn 100% of calories from fat at rest, it's more like 60-70% of calories burned at rest. And to take it further it's 60-70% of calories burned are from fat as long as you are in aerobic metabolism, which is up to 70% of your maximal heart rate.