By GRETCHEN REYNOLDS New York Times
Exercise may help people avoid regaining weight after successful dieting, according to a new study. It shows that exercise can crucially alter the body’s response to weight loss and potentially stop unwanted pounds from creeping back on.
The study, published this month in Medicine & Science in Sports & Exercise, offers rare good news about exercise and body weight. As readers of the Phys Ed column know, the relationship between the two is tangled. Multiple past studies have found that exercise alone — without food restriction — rarely reduces weight and frequently adds pounds, since many people feel hungry after workouts and overeat.
In general, most nutrition experts agree that to lose weight, you must reduce calories, whether you exercise or not. Take in fewer calories than your body burns and by the ineluctable laws of math, you will drop pounds.
Unfortunately, that same heartless math dictates that weight loss then makes it difficult to stay thin. After losing weight, your body burns fewer calories throughout the day than it did before, because you have less body mass using energy.
Meanwhile, for reasons that are not fully understood, many people become more sedentary after they lose weight. Studies show that non-exercise activity thermogenesis, or N.E.A.T. — a measure of how much energy people use to stand, fidget, walk to the car and otherwise move around without formally exercising — often declines substantially after weight loss, perhaps because the body thinks you are starving and directs you to stay still and conserve energy.
The upshot is that successful dieters typically burn fewer calories each day than they did when they were heavier, which sets them up for weight regain.
Enter exercise. Past studies have found that people who begin or continue an exercise program after losing weight are less likely to experience as much regain. But scientists have been less clear about how exercise protects against rebound pounds, and what types of exercise might be best.
So researchers at the University of Alabama at Birmingham decided to closely study the effects of exercise during that pivotal time just after someone has reached his or her goal weight.
They began by recruiting about 100 overweight, sedentary women, all of whom agreed to undertake a stringent diet, consisting of only 800 calories per day. The women also completed an array of baseline tests to determine their body composition, resting metabolic rate, daily levels of N.E.A.T., and walking economy, which tells scientists how easy it is for them to move around. The Alabama researchers also used an elaborate equation to establish how much time the women were moving each day.
Then a third of the women were asked not to exercise.
Another third began a supervised aerobic exercise program, consisting of about 40 minutes of walking or jogging on a treadmill at a brisk pace three times a week.
The final third started supervised upper- and lower-body weight training three times per week.
Each woman, whether she exercised or not, stayed on the 800-calorie daily diet until she had lost 25 pounds. At that point, she continued to follow the exercise instructions and transitioned for a month to a customized, supervised diet designed to keep her in energy balance, or at a level intended to make her neither gain nor lose weight. The scientists wished to focus more on movement patterns than eating habits.
What they found was that the women who did not exercise generally did not move much either. They spent fewer minutes each day in motion than they had before their weight loss. Their levels of N.E.A.T. fell significantly. Their resting metabolic rates also declined, since they weighed less. Over all they were burning considerably fewer calories each day than before they had shed the 25 pounds.
Meanwhile, the women who exercised had a drop-off in their resting metabolic rates after losing the weight, as expected, but much less of a slump in their everyday movements. Their levels of N.E.A.T. — the calories they burned in activities apart from exercise — declined only slightly for the exercising volunteers as a group, and some women increased how much they moved. They walked, stood, took the stairs and fidgeted more than they had before their weight loss.
This increase in N.E.A.T. was most common among the women who weight trained. Those who lifted weights also, interestingly, tended to have better walking economy; movement felt easier for them than it did before the weight loss. At the same time, many of the women who did not exercise showed worse movement economy, even though they now weighed less.
Over all, the data suggest that exercise — and, in particular, weight training — after weight loss prompts people to move more throughout the day, said Gary R. Hunter, a distinguished professor in the department of human studies at the University of Alabama at Birmingham and lead author of the study. As a result, they burn more calories and, with some discipline about food intake, should stave off weight regain.
This study, though, was relatively short-term and narrow, using only female volunteers and following them for only a month. Whether the results would be similar over a longer period, for men, or for those who begin exercising only after they have lost weight remains to be determined, Dr. Hunter said.
But even so, “It seems clear that exercise is very important if you wish to keep the weight off,” he said.