Busting the Great Myths of Fat Burning

Your body burns either fat or carbs depending on the intensity of your activity. But when it comes to losing weight, calories are calories. You burn fat even when you're in couch-potato mode. Yet, a lot of misunderstanding prevails.

Get ready to break down some of the myths people have about burning fat:

  • Myth: The body completely shuts off one fuel source when it turns on the other.
    The Truth: What has often been misunderstood by both exercisers and exercise instructors alike is that the body relies on both fat and carbs for energy all the time, albeit in different ratios. In fact, as you sit here reading, you may be burning about 50-60 percent fat and 50-40 percent carbohydrates. You're not using much of either, however, because the amount of calories you need probably amounts to about one or two calories a minute. If you were to get up and start jogging in place, your body would need to supply you with some quick energy to do so, so the metabolism ratio might shift to drawing upon more carbohydrates, say 70 percent, and less fat, say 30 percent. If you were to continue jogging, then, in order to preserve the carbs (which can run out since you have limited stores in the body), your body would gradually shift its metabolism ratio again to say, 60 percent fat and 40 percent carbohydrates. From an energy efficiency point of view, it pays to be fit. The endurance athlete would be able to make the shift sooner, and his fat-burning percentage might be 65-75 percent.
    However, in practical terms this is purely technotalk, and these ratios don't make a big difference when it comes to losing weight and decreasing your body fat. For the most part, athletes are often leaner not because they might rely on slightly more fat for fuel, but because they practice their sport two to three, or more, hours a day — this burns a lot of calories. If you had the time, energy, and fitness level to work out three hours a day, being overweight would probably not be an issue. To lose weight, you need to burn more calories than your body consumes and uses everyday. Exercise is one main way to burn a lot of calories. But when it comes to weight loss, what matters is how many calories you burn, not so much whether they are fat or carbohydrate calories.
  • Myth: Exercise done at a low intensity, such as walking, is better at fat burning than other high-intensity activities, like running or cardio activities where you push yourself very hard.
    The Truth: In a strict scientific sense, these claims are true because working at a lower intensity requires less quick energy and a higher percentage of fat is burned. But you'll also burn fewer calories than you would if, for the same amount of time, you work out at a harder intensity (running versus walking). If you're trying to lose weight, even though a higher percentage of fat is being used, a lower total amount of fat is lost.
    Whether increased fat burning will result in actual weight loss is dependent upon several variables, including the total calories burned (which include both fat and carbohydrate calories) and the total fat calories burned. If you do work at a low intensity, you need to increase the time spent exercising to burn more calories. What matters most is the total number of calories burned. If you burned 250 calories every day from a short, fast jog, you'd see a bigger difference in weight and fat loss than if you walked everyday for the same amount of time. The number of fat calories you burn isn't that important, because even if you burn a lot of carb calories, these need to be replaced both by the carbs you eat in your diet and also within your body. Your fat stores will be broken down and transformed into carbohydrates when you need fuel. Even if you're burning lots of carb calories and less fat calories through exercise, your fat still inevitably gets used.
    It boils — not burns — down to this: During the same amount of time you don't use more calories at lower exercise intensities. If you're trying to lose weight and you have only 30 minutes to work out, you would burn fewer calories walking at a moderate pace compared to walking at a fast pace. Working out at higher intensities may cause you to burn a lower percentage of fat, but since you burn more total calories, you still use more fat calories.
    Low- to moderate-intensity exercise can burn a significant number of calories over a period of time. If you aren't fit enough to push yourself to work at a high intensity, or you have a physical weakness that prevents you from doing so, you can still burn a lot of calories by doing low-intensity workouts for a longer period of time.
  • Myth: Running, cycling, or other cardio activities are more fat burning once you've been doing them for more than 15 or 20 minutes.
    The Truth: Technically, once you've been exercising for 15 or 20 minutes, your body has made the shift to using a higher percentage of fat for fuel. But again, if you're trying to lose weight, it's about the total number of calories burned, not necessarily the fuel source.
    For example, say that at rest you burn up to 60 percent fat. When you enter the initial phases of intense exercise, the ratio changes. You may now burn only 30 percent fat because your body is using quick-energy carbohydrates. Once the exercise is sustained, the body switches back to using a higher percentage of fat to fuel the movement (up to 75 percent fat). In this aerobic phase of exercise, a higher percentage of fat is being used for energy. But if you aren't working out for a very long period, you may still burn more total calories and, therefore, more fat calories working out harder. Put another way, if burning as many calories as you can is the best way to lose weight, even a dummy can figure out which activity of the following is going to give the best results (answer: jogging and sprinting), even though their fat-burning quota is on the low end of the ratio.

Activity

Calories Burned

Fat Percentage

Calories from Fat

Watching TV for 20 minutes

40 calories

60 percent

24 calories

Walking for 20 minutes

100 calories

65 percent

65 calories

Jogging & sprinting for 20 minutes

250 calories

40 percent

100 calories

Comments (11)

  1. Posted by rdiroma
    I think the article about "Busting the Great Myths of Fat Burning" is confusing at best and wrong or misleading in this article. Perhaps a more qualified person can correct the errors. E.G ,it mentions that only fat and carbohydrates are burned for energy. It's known that protein can also be a fuel source. A few more errors can be found.
  2. Posted by Erin Carraway
    FINALLY! This is one of the best articles I have seen regarding how a body uses fat and carbohydrate to fuel the body. Not since my exercise physiology classes have I seen such a great explanation. Yes - It is a bit confusing, mainly because so much misinformation is out there to counter. Well done! (note: protein can be burned, but only when there is a dearth of carbohydrates and fat to pull from. It can be very dangerous as well, as the ketones add up and the body (kidneys?) have a difficult time removing waste products from the broken down protein.) Erin@obesityfreeforlife.com
  3. Posted by seemetri
    YEAH! I've been explaining this for years to other fitness professionals who have fallen into this fat burning zone trap! Thank you for explaining this in such a basic way that all can understand!
  4. Posted by Lal
    This is not the first time iv'e read an article like this, and i also have tried it by striking a balance between both high intensity and low with great results. am now starting it over once again
  5. Posted by Garret
    I have lost over 50 pounds in the past month by lowering my calorie income and mixing high intensity with low intensity workouts. (mostly riding a exercise bike) I have been looking all over google for this info. The secret is how you warm up and make that switch from burning calories to burning fat. Don't eat at night and try to workout 5 or more days a week, but remember your body needs to recover. Mixing up your workout helps also. Protien is important to repair your muscles mostly, so be careful and find the perfect mix between your protien intake and the kind of workout you are doing. Try to take no less and no more than two days off in a row or you will loose the forward progress you have made. I don't want to say and I know people won't like this but I believe the "starvation mode" is a myth, the idea came from the concept that we are like cave men and our body conserve fat if we don't eat a lot so we will have energy to hunt and survive later down the road. As a life form we evolve just as animals and other life forms evolve. It works for me as long as I am careful doing it, I still eat a small meal a day. One more thing WATER! WATER! WATER! And nothing else.
  6. Posted by Michele
    The major point here is that you consistently work out, mixing it up seems to help. I also have looked all over to find out about burning carbs...this is the first place that finally gave me some explanation.
  7. Posted by cherry
    I actually bookmarked this page
  8. Posted by Yauhoooo
    Hi, I found your site using http://www.yauhoooo.com Yauhoooo, does your site support Firefox?
  9. Posted by Steven Smith
    Garret, please tell me that you eat more than one small meal a day.
  10. Posted by tkmslee
    Personal experience has proven to me, time after time, that high intensity sprinting 2 -3 times a week will burn fat more effectively than long slow-burn type of exercises. I have seen this in my own training again and again, I have even gotten in the trap of believing that low intensity jogging is best...but every time I go back to sprinting, I loose a lot more weight.
  11. Posted by Robinson Cruz
    I guess this comment should be called "busting the great myths of busting the great myths of fat burning." The article is correct that calories count, but it is not correct that a calorie is a calorie, or that glycogen burned preferentially over fat in high-intensity exercise can be replaced from fat stores. Fat stored in adipocytes has no biochemical pathway to contribute significantly to replenishment of glycogen. So if two exercise regimens use the same number of calories, lower intensity exercise will reduce body fat more than high-intensity exercise (>65% VO2max). Yes, if you jog instead of running or running/sprinting, you will burn calories more slowly, requiring longer exercise. But jogging IS the better way to reduce fat stores in the body. See this review article for biochemical pathways for replenishing muscle and liver-based glycogen after high-intensity execise. Notice no mention of using fat to replenish glyogen. http://ajpendo.physiology.org/cgi/content/abstract/253/3/E305

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