Fat Burning Zone -- Is it real?

Question

Does low-intensity, long-duration exercise really "burn fat" at rates higher than highly aerobic exercise? Is the academic case for this view actually strong? It seems like a lot of accepted knowledge in the exercise industry has a weak scientific basis.

Answer 1

From the American Council on Exercise:

In a 30-minute aerobic exercise:

Low Intensity (50% of maximum exercise capacity):
- you'll burn approx. 200 calories, 120 of them from Fat (60%)

High Intensity (75% of maximum exercise capacity):
- you'll burn approx. 400 calories, 140 of them from Fat (35%)

So,

while it is true that a higher proportion of calories burned during low-intensity exercise come from fat (about 60 percent as opposed to approximately 35 percent from high-intensity programs), high-intensity exercise still burns more calories from fat in the final analysis.

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Dummies.com concurs:

... 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 (e.g. running versus walking).

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.

The conclusion is:

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.

Answer 2

Looks like you are right and the fat burning zone is a bit of a falicy. To quote this research:

And they also have this table to show the results:

At 9 times the fat burning power of low intensity exercise I know what i'm going to be doing to lose weight!

** Edit **

I guess I need to clarify this. The study above is trying to debunk some of the conventional wisdom about the fat burning potential of exercise regimes. Two regimes were run, a low intensity study programme (ET) and a high intensity study programme (HIIT).

To add another table from the link study:

looking at the bottom row of the table, you can see that the ET group lost (ignoring the +/- to make the math easier) 4.5 subcutaneous skinfolds, whereas the HIIT group lost 13.9 subcutaneous skinfolds.

The ET programme resulted in more total time working out and used 120.4 +/- 31.0 MJ of energy. The HIIT programme resulted in less total time working out and used 57.9 +/- 14.4 MJ of energy.

Or from a percentage point of view the HIIT group did roughly 48% (57.9/120.4 for the percentage) of the work that the ET group did, but the people on the HIIT study lost more body fat (note that average overall weight loss was virtually non-existant for both groups).

If you now take that 48% and extrapolate it up to 100% it works out at an equivalent subcutaneous skinfolds loss of 28.99 (13.9/0.48), this equates to about 6.5 times as much subcutaneous skinfold loss. Now i'm not a mathmatician, and I have only taken one row on the table into account without taking any standard deviations into account the the above workings out are going to be messy and inaccurate, but they should hopefully illustrate the point.

High impact workouts are better at reducing body fat than low impact workouts and the point of this study was to debunk the conventional wisdom given by health professionals.