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Hey, Time, 'Exercise won't make you thin'? What were you thinking?

August 11, 2009 |  5:00 am

Exercise Fitness and health experts say Time magazine got it wrong this week with its cover story, "Why Exercise Won't Make You Thin." The story argues that even though more people than ever are exercising, obesity rates are still rising. Moreover, the article posits that exercise backfires as a weight-loss tool because people become hungrier and end up eating more. The rationale goes something like this: "I walked three miles today so I'll reward myself with a blueberry muffin." The three-mile walk burned off 239 calories, but the muffin added 420.

Further, the story argues, humans evolved to hoard calories. Once you gain a certain amount of weight, your body tries to protect that fat storage. Indeed, this theory is widely supported and does explain in part why efforts to lose weight, either by diet, exercise or both often fail.

However, most research suggests that exercise and dieting are both important for weight loss and that exercise is critical for weight maintenance. It's difficult, but not impossible. Research not cited by the Time article shows that people who have maintained a significant weight loss over a sustained period of time largely rely on exercise to do so. This effort, studies suggest, can eventually retrain the body to respond appropriately to food and activity. Moreover, these people also carefully watch what they eat. In other words, they know that eating a blueberry muffin after their workout will undermine their goals. This evidence was detailed in a 2008 story in the Los Angeles Times' special Health section on weight loss.

The American College of Sports Medicine released a statement Friday saying it takes "strong exception" to the Time story's conclusions. "[P]hysical activity is one of the most important behavioral factors in enhancing weight loss maintenance and improving long-term weight loss outcomes," said John Jakicic, who chairs the ACSM's committee on obesity prevention.

One expert quoted in the Time piece, Dr. Timothy Church, said his professional opinions were misrepresented, according to the ACSM statement. Church noted that weight maintenance is different than weight loss. Virtually all people who lose weight and keep it off are exercising to maintain weight, he said.

Another ACSM member, Dr. Janet Rankin, said: "A practical response to the claim that exercise makes you eat more and gain weight is to look around. If this were the case, wouldn't those who regularly exercise be the fattest? Obviously, that isn't the case."

The story doesn't say exercise is bad. Indeed, exercise has been shown to convey many health benefits. It just won't help you lose weight, the author, John Cloud, states. But he seems to be suggesting that promoting exercise is some type of public health conspiracy.  "Public-health officials have been reluctant to downplay exercise because those who are more physically active are, overall, healthier," he said.

-- Shari Roan

Photo credit: Buster Dean  /  Houston Chronicle / Associated Press

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