September 26, 2010

Beware the Fat Burning Zone!

  So you’re all warmed up and motivated to burn some fat.  You punch in the “fat burning” button on the treadmill or elliptical, ready to get results.  Well guess what?  If your goal is to lose weight, you are sabotaging yourself. It’s a mystery in the fitness industry why equipment makers label their machines like this; the fat burning zone is basically a myth, and will not help you lose weight.
 There is a tiny bit of science behind the fb zone; but if you are trying to lose weight, the numbers do not add up.  It is true that when you exercise at a lower intensity (the purported fat burning zone) that you use a higher percentage of fat for fuel than at a higher intensity.  However, you are burning fewer calories, and therefore will burn fewer fat calories unless you exercise for a longer time.  For example, say you work out in the fb zone for 30 minutes; depending on your weight and metabolism you may burn about 200 calories.  Assume half the calories come from fat, so you’ve burned 100 fat calories.* Now ramp the intensity up (to a level where you can still talk, but probably can’t sing) and you may burn up to 300 calories.  Now 40% of that fuel may be from fat, so you will have burned 120 fat calories, and 100 more total calories.  Which do you think will help you lose weight?
Now I am not saying it is bad to workout in this zone.  If you are new to exercise or have limitations, this level of intensity may be all you can handle.  However, if you are physically fit and trying to lose weight, you are doing yourself a disservice.  So what is the “right” way?  More on that next time.

*Numbers are examples, but you can find the exact fuel percentages here:
Thompson, D.L., et al. 1998. Substrate use during and following moderate- and low-intensity exercise: Implications for weight control. European Journal of Applied Physiology and Occupational Physiology, 78 (1), 43-49.

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