There's a lot of attention paid to what works when it comes to losing weight. But that's not really the hard part; anyone can diet or exercise in the short term. Maintaining a loss, avoiding age-related weight creep, and keeping up healthful habits over time are much more difficult. That's why the researchers behind a new study, published this week in the Journal of the American Medical Association, wanted to examine the habits of people who were eating what they considered a normal diet and were "living life as usual," says one of the authors, I-Min Lee, an associate epidemiologist at Brigham and Women's Hospital in Boston and associate professor of medicine at Harvard Medical School. And they made some interesting discoveries about the power of exercise.
That may sound like bad news for people of normal weight who aren't exercising that much, not to mention everyone who is overweight or obese, says Lee. But it doesn't mean that physical activity of less than 420 minutes a week is worthless. Working out at a moderate intensity for 150 minutes a week, as the government recommends, is associated with a lower risk of many chronic diseases, no matter your weight.
But it does underline that exercise on its own, with no attention paid to calories, is unlikely to carve away excess weight or prevent gain. (Even people training for a marathon can gain weight; it's far easier to eat than to burn off what you eat.) Remember that none of these women were consciously dieting. The study can't say whether exercise is useless for overweight or obese women who are actively attempting to lose weight by also changing their eating habits. And that "usual diet" consumed by the women probably differs by their weight. It's likely that normal-weight women eat fewer calories as a matter of routine, without thinking of it as a diet.
Yet exercise also appears to be an important factor in maintaining a healthy weight, according to this and other studies. Research published in 2008 found that women who dieted and were then able to keep off 10 percent of their body weight for two years also exercised more than the government recommends, about 275 minutes a week. The amount of exercise needed to sustain a healthy weight may be in question, but the principle is consistent: Get out there and move.