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Phys Ed Gretchen Reynolds on the science of fitness.

If you are aiming to lose weight by revving up your exercise routine, it may be wise to think of your workouts not as exercise, but as playtime. An unconventional new study suggests that people’s attitudes toward physical activity can influence what they eat afterward and, ultimately, whether they drop pounds.

For some time, scientists have been puzzled — and exercisers frustrated — by the general ineffectiveness of exercise as a weight-loss strategy. According to multiple studies and anecdotes, most people who start exercising do not lose as much weight as would be expected, given their increased energy expenditure. Some people add pounds despite burning hundreds of calories during workouts.

Past studies of this phenomenon have found that exercise can increase the body’s production of appetite hormones, making some people feel ravenous after even a light workout and prone to consume more calories than they expended. But that finding, while intriguing, doesn’t fully explain the wide variability in people’s post-exercise eating habits.

So, for the new study, published in the journal Marketing Letters, French and American researchers turned to psychology and the possible effect that calling exercise by any other name might have on people’s subsequent diets.

In that pursuit, the researchers first recruited 56 healthy, adult women, the majority of them overweight. The women were given maps detailing the same one-mile outdoor course and told that they would spend the next half-hour walking there, with lunch to follow.

Half of the women were told that their walk was meant to be exercise, and they were encouraged to view it as such, monitoring their exertion throughout. The other women were told that their 30-minute outing would be a walk purely for pleasure; they would be listening to music through headphones and rating the sound quality, but mostly the researchers wanted them to enjoy themselves.

When the women returned from walking, the researchers asked each to estimate her mileage, mood and calorie expenditure.

Those women who’d been formally exercising reported feeling more fatigued and grumpy than the other women, although the two groups’ estimates of mileage and calories burned were almost identical. More telling, when the women sat down to a pasta lunch, with water or sugary soda to drink, and applesauce or chocolate pudding for dessert, the women in the exercise group loaded up on the soda and pudding, consuming significantly more calories from these sweets than the women who’d thought that they were walking for pleasure.

A follow-up experiment by the researchers, published as part of the same study, reinforces and broadens those findings. For it, the researchers directed a new set of volunteers, some of them men, to walk the same one-mile loop. Once again, half were told to consider this session as exercise. The others were told that they would be sightseeing and should have fun. The two groups covered the same average distance. But afterward, allowed to fill a plastic bag at will with M&M’s as a thank-you, the volunteers from the exercise group poured in twice as much candy as the other walkers.

Finally, to examine whether real-world exercisers behave similarly to those in the contrived experiments, the researchers visited the finish line of a marathon relay race, where 231 entrants aged 16 to 67 had just completed laps of five to 10 kilometers. They asked the runners whether they had enjoyed their race experience and offered them the choice of a gooey chocolate bar or healthier cereal bar in consideration of their time and help. In general, those runners who said that their race had been difficult or unsatisfying picked the chocolate; those who said that they had fun gravitated toward the healthier choice.

In aggregate, these three experiments underscore that how we frame physical activity affects how we eat afterward, said Carolina O.C. Werle, an associate professor of marketing at the Grenoble School of Management in France, who led the study. The same exertion, spun as “fun” instead of “exercise,” prompts less gorging on high-calorie foods, she said.

Just how, physiologically, our feelings about physical activity influence our food intake is not yet known, she said, and likely to be bogglingly complex, involving hormones, genetics, and the neurological circuitry of appetite and reward processing. But in the simplest terms, Dr. Werle said, this new data shows that most of us require recompense of some kind for working out. That reward can take the form of subjective enjoyment. If exercise is fun, no additional gratification is needed. If not, there’s chocolate pudding.

The good news is that our attitudes toward exercise are malleable. “We can frame our workouts in different ways,” Dr. Werle said, “by focusing on whatever we consider fun about it, such as listening to our favorite music or chatting with a friend” during a group walk.

“The more fun we have,” she concluded, “the less we’ll feel the need to compensate for the effort” with food.