From both physicians and fitness gurus, the mantra for effective weight loss is the same: diet and exercise. And we’ve all had friends who gushed about starting a modest walking program, for example, and saw themselves drop unwanted pounds.

All this flies in the face of the math of exercise. If you’ve ever watched the calorie counter on your treadmill or Stairmaster, you know how painfully slowly the “calories burned” number climbs. A vigorous session may burn only a few hundred calories - an amount that could be consumed in a minute with a rich dessert. Not to worry, we’ve been told - even after you stop your workout, your body’s metabolism remains in high gear for many hours.

Now, researcher Edward Melanson, an exercise physiologist and associate professor of medicine at the University of Colorado in Denver, has shown that the supposed long-term metabolism boost doesn’t really happen. But, before your cancel your gym membership, there may be a way that exercise does help you lose weight, even if it’s not the mechanism promoted by fitness experts for years. First, the bad news:

In the new report, published in the journal Exercise and Sport Sciences Reviews, Melanson and colleagues discuss research to date on the issue of burning fat during and after exercise. The authors conclude that while people do burn more fat when they are exercising than when they are not, they have no greater ability to burn fat over the next 24 hours than on days when they are couch potatoes.

Melanson says other experts in his field have been “flabbergasted” by the results.

“Bottom line is that we once thought that exercise would burn calories, especially fat calories, for a long period after a bout of exercise,” says exercise physiologist Gerald Endress, fitness director for the Duke University Diet and Fitness Center who was not involved in the research. “This does not seem to be the case.” [From MSNBC - Exercise not likely to rev up your metabolism by Jacqueline Stenson.]

How do we square this with the experience of so many experts and individuals? The answer may lie in our brains. In Reverse Neuromarketing: Exercise Resets Brain, I reported on recent research showing that exercise reduced the craving for tobacco. Specifically, researchers at the University of Exeter showed that just 10 minutes of working out on a stationary bicycle negated the ability of smoking images to light up the areas of the brain associated with cravings. fMRI brain scans were used to demonstrate the effect of the light exercise.

So, perhaps your doctor and your personal trainer are right, but for the wrong reason. Even if modest exercise burns relatively few calories and doesn’t kick your metabolism into high gear for the rest of the day, perhaps it DOES help quiet some cravings in a manner similar to the smoking study results.

If exercise does indeed reduce food cravings, it would seem the best time to schedule it would be at those times when one is likely to snack. It would also seem that while a sweaty, hour-long workout might be great for your cardiovascular health and muscle tone, craving reduction could be accomplished with a much shorter session of walking, cycling, or other light exercise.

I’m looking forward to seeing how those involved in weight loss counseling adapt to the new information about how ineffective exercise is at burning calories, and I hope that someone attempts to extend the tobacco fMRI studies to food cravings.

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