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Why exercise is so helpful with weight loss

Published October 01. 2011 09:01AM

I have always extolled the benefits of exercise.

Exercise regularly and you improve your mood, intellectual capacity, quality of sleep, flow of nutrients, tolerance of stress, tolerance of pain, and your cholesterol and blood sugar levels; reduce your risk of heart disease, stroke, diabetes, osteoporosis, and certain cancers; and lower your heart rate, blood pressure, and degree of joint pain.

In fact, exercise is such an all-around elixir that the last time I taught a class on health and fitness and students asked how to best lose weight, I said that dieting was a waste of time unless you augmented it with exercise.

To reinforce this, I mentioned landmark research performed by Albert Stunkard at the University of Pennsylvania in 1959 that found the dieting failure rate to be 95 percent and how new estimates, such as the one by Judith Matz and Ellen Frankel, licensed clinical social workers and co-authors of The Diet Survivor's Handbook (Sourcebooks, 2006), had it as high as 98 percent.

Yet The National Weight Control Registry, an ongoing research study, has uncovered at least 5,000 Americans 18 years of age and older who have lost an average of 66 pounds and kept it off for an average of 5.5 years. In searching for patterns to this group's success, the researchers found surprise, surprise that 90 percent of the registrants, along with modifying their food intake, typically exercised one hour a day.

Being able to spew out statistics like that may have impressed the class, but I have a confession to make. At that time, I wasn't quite sure why exercise made such a difference.

Sure, I knew, for example, that a 150-pound female who runs 3.3 miles in 30 minutes burns 374 calories, but that's exactly why I was unsure why exercise is so crucial to successful dieting. That caloric expenditure really isn't that great not when you consider how calorie-dense foods are these days.

The calories in a McDonald's Quarter Pounder with cheese and a small order of their French fries, for instance, are twice the calories expended during that woman's 30-minute run.

And yes, I am aware of what's called the after-burn effect of exercise, but that caloric expenditure isn't nearly as great as first thought. Based on the research published in the February 2011 issue of Medicine & Science in Sports & Exercise, that run causes that woman to burn another 140 calories over the next 12 hours.

So even with the after-burn effect, the 150-pound female runner who runs 3.3 miles in 30 minutes and eats a Quarter Pounder with cheese and a small order of fries is left with an excess of 235 calories.

Do you see why I always thought there had to be another element to exercising that aided dieting? It's just that until Medical News Today wrote about the study that researchers from Johns Hopkins University presented at the annual meeting of the Society for the Study of Ingestive Behavior last July I didn't know what it was.

They found that exercise influences the release of hormones before and after meals hormones that influence how much you eat.

At least that's what happened at Johns Hopkins to lab rats.

In the study, the researchers fed rats an appetizing meal and then checked the degree to which hormones were secreted. The rats seen as regular exercisers by virtue of their running wheel workouts secreted higher amounts of amylin, a hormone secreted by the pancreas that's, according to Medical News Today, "known to inhibit food intake, slow digestion, and reduce the rate at which glucose enters the bloodstream," when compared to sedentary rats.

Additionally, the rate at which ghrelin, a hormone that's known in rats and humans to be an appetite stimulator, left the stomachs and bloodstreams of the regular exercisers faster.

Later, the researchers gave all the rats an injection of cholecystokinin, another hormone known to decrease food intake, and found the injection decreased food intake more in the rats that exercised than the rats that did not.

The findings of this study are significant because of the strong physiological similarities between humans and rats that's why they're so often used in medical research. As a result, there's probably more than a good chance that exercise affects hormone secretion in human in a similar manner.

If so, that means frequent exercisers are getting an additional benefit beyond the expenditure of calories during the workout and through the after-burn afterwards. In all likelihood, a secretion of hormones spurred is making them feel fuller faster.

And making dieting easier.

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