The next few months, filled with holiday feasting, represent a dire threat to most people’s waistlines. Even those of us who normally eat a wholesome diet can find ourselves gorging on fatty, high-calorie foods and gaining the annual Christmas inner tube. But several new studies promote a simple and effective response: Run or walk from the buffet. Even if you’ve already overindulged, the studies suggest, exercise can lessen or reverse the unwelcome consequences.
For the studies, Paul T. Williams, a staff scientist in the life sciences division at Lawrence Berkeley National Laboratory, enlisted the help of more than 100,000 runners and, for a second study published last week in the journal Obesity, almost 40,000 walkers. He had each group fill out extensive questionnaires that asked about their running or walking history, including when they’d begun running more than 12 miles a week or walking at least half a mile most days of the week, as well as, for the runners, their current mileage, best race times, numbers of recent marathons, and so on. The questionnaire also asked about current and previous body weight: how much they had weighed when they started exercising, what they weighed now, their waist size and height. Finally, the volunteers were asked about eating habits, and specifically, how much red meat (beef, pork and lamb) they consumed each week and how many servings of fruit they ate each day.
“We used servings of meat and fruit as markers of the overall quality or type of the diet,” Dr. Williams says. People who frequently eat meat and rarely have fruit are more likely, over all, to be eating a fattier, higher-calorie and potentially less healthy diet, he says.
Certainly, in his new research, they weighed more. Among both the runners and walkers he studied, whether male or female and whatever their age, those who ate more meat and fewer servings of fruit tended to have a higher body mass index, an indicator of overall body fat, than those who ate less meat and more fruit. They had also gained significantly more weight over the years.
Unless they exercised diligently. The more someone walked or, even more strikingly, the more they ran, the less likely they were to have gained large amounts of weight, even if they ate what the study politely calls a “high-risk diet.” Runners who ticked off about five miles a day stayed relatively lean over the years, even if they regularly consumed a meaty and presumably high-fat diet. Most still had gained some pounds, according to their running and weight histories, but less than would have been expected, given their eating habits.
“Usually, B.M.I. and waist circumference increase if you eat more meat and less fruit,” Dr. Williams says. But his data indicate that exercise reduces this effect. The more miles run, the less a person is likely to be affected by questionable dietary choices or by what Dr. Williams calls “lapses, like those that happen during the holidays.”
These are hardly the first studies, of course, to suggest that exercise can help to control weight or reduce the depredations of an imperfect diet. A 15-year study of more than 30,000 middle-aged women by Harvard researchers found that while virtually all of the women gained weight over the years, those who walked about an hour a day gained the least, averaging less than five added pounds over the 15 years. The study did not examine eating patterns, though.
An interesting animal study published this year looked directly at the effects of exercise on rats eating a high-fat diet, however. The rats were given free access to fatty foods for 12 weeks, by which time they all had become rotund and developed metabolic syndrome, a constellation of unhealthy conditions that includes insulin resistance, poor cholesterol levels and high blood pressure. Then the researchers divided the animals into several groups, with some remaining on the high-fat diet but running every day, while others were switched to a standard kibble, and still others changed nothing. This new program also lasted 12 weeks.
By the end of that time, the rats that ran had managed to “reverse almost all the atherosclerotic risk factors linked to obesity,” the researchers found, even though they remained on the high-fat diet. They also had stopped gaining weight. The rats that had been switched to a standard diet but didn’t run improved their metabolic profiles, too, but not as much as the running rats. The researchers speculate that exercise activates certain metabolic pathways that undo the damage of a high-fat diet, even if that diet continues.
Dr. Williams suspects that similar mechanisms are at work in human exercisers, and that the effects are commensurately greater the more a person exercises. “It’s well established that endurance training enhances the body’s ability to burn fat” from foods, he says, so serious runners can incinerate the fat marbling a serving of beef before it is stored as flab around the waist. Which means that, if you work out dutifully, you should “get through the holidays without too many regrets,” he says.
