Thursday, July 26, 2012
WHY EXERCISE WON'T MAKE YOU THIN
And yet obesity figures have risen dramatically in the same period: a third of Americans are obese, and another third count as overweight by the Federal Government's definition. Yes, it's entirely possible that those of us who regularly go to the gym would weigh even more if we exercised less. But like many other people, we get hungry after we exercise, so we often eat more on the days we work out than on the days we don't. Could exercise actually be keeping us from losing weight?
The conventional wisdom that exercise is essential for shedding pounds is actually fairly new. As recently as the 1960s, doctors routinely advised against rigorous exercise, particularly for older adults who could injure themselves. Today doctors encourage even their oldest patients to exercise, which is sound advice for many reasons: People who regularly exercise are at significantly lower risk for all manner of diseases — those of the heart in particular. They less often develop cancer, diabetes and many other illnesses. But the past few years of obesity research show that the role of exercise in weight loss has been wildly overstated.
"In general, for weight loss, exercise is pretty useless," says Eric Ravussin, chair in diabetes and metabolism at Louisiana State University and a prominent exercise researcher. Many recent studies have found that exercise isn't as important in helping people lose weight as you hear so regularly in gym advertisements or on shows like The Biggest Loser — or, for that matter, from magazines like this one.
The basic problem is that while it's true that exercise burns calories and that you must burn calories to lose weight, exercise has another effect: it can stimulate hunger. That causes us to eat more, which in turn can negate the weight-loss benefits we just accrued. Exercise, in other words, isn't necessarily helping us lose weight. It may even be making it harder.
You might think half a muffin over an entire day wouldn't matter much, particularly if you exercise regularly. After all, doesn't exercise turn fat to muscle, and doesn't muscle process excess calories more efficiently than fat does?
Yes, although the muscle-fat relationship is often misunderstood. According to calculations published in the journal Obesity Research by a Columbia University team in 2001, a pound of muscle burns approximately six calories a day in a resting body, compared with the two calories that a pound of fat burns. Which means that after you work out hard enough to convert, say, 10 lb. of fat to muscle — a major achievement — you would be able to eat only an extra 40 calories per day, about the amount in a teaspoon of butter, before beginning to gain weight. Good luck with that.
All this helps explain why our herculean exercise over the past 30 years — all the personal trainers, StairMasters and VersaClimbers; all the Pilates classes and yoga retreats and fat camps — hasn't made us thinner. After we exercise, we often crave sugary calories like those in muffins or in "sports" drinks like Gatorade. A standard 20-oz. bottle of Gatorade contains 130 calories. If you're hot and thirsty after a 20-minute run in summer heat, it's easy to guzzle that bottle in 20 seconds, in which case the caloric expenditure and the caloric intake are probably a wash. From a weight-loss perspective, you would have been better off sitting on the sofa knitting.