the fact of doing physical exercises make us hungry afterwards and prone to eating more than we should? Or does it lessen our appetite and make it easier for us to skip that last tempting slice of pie?
A new study provides timely, if cautious, clues. The study, which involved sedentary, overweight men and women and various types of moderate exercise, found that people who exercised didn’t overeat at an attractive buffet lunch afterward. However, they also didn’t skip dessert or skimp on portions. The findings provide a reminder during the holiday season that while exercise has numerous health benefits, helping us eat less or lose weight may not be among them.
For most of us, the exercise affects our weight and hunger in unexpected and sometimes contradictory ways. According to several scientific studies, few people who start exercising lose as many pounds as the number of calories they burn would predict.
Some recent research suggests that this is because our bodies stubbornly try to cling to our fat stores, an evolutionary adaptation that protects us against (unlikely) future starvations. Therefore, if we burn calories during exercise, our bodies can make us sit more soon afterward or reallocate energy from some bodily systems to others, reducing our overall daily energy expenditure. In this way, our bodies unconsciously compensate for many of the calories we burn during exercise, reducing our chances of losing weight through exercise.
But this caloric compensation happens slowly, over weeks or months, and involves energy expenditure. It has become less clear whether and how exercise influences our energy consumption—that is, how many servings of food we consume—especially in the hours immediately following a workout.
Exercise for the sake of science
The evidence so far is mixed. Some studies indicate that exercise, especially if it’s strenuous and prolonged, tends to decrease people’s appetite, often for hours or even the next day. This phenomenon leads them to eat fewer calories in subsequent meals than if they hadn’t exercised. But other studies suggest the opposite, finding that some people feel hungrier after exercising anyway and soon replace the calories they expended — and others — with an extra serving or two at the next meal.
Many of these studies, however, were based on healthy, fit, and active young men and women, as these groups tend to be available among students in the exercise science departments at universities. Few experiments have looked at how exercise can immediately affect the appetite and eating of older, overweight, and sedentary adults, and even fewer have studied the effects of resistance training and aerobic exercise.
The new study was published in October in Medicine & Science in Sports & Exercise. Scientists at the University of Utah in Salt Lake City, the Anschutz Medical Campus at the University of Colorado in Aurora, Colorado, and other institutions announced that they wanted volunteers in Colorado willing to exercise and eat, for the sake of science.
After hundreds of responses, they were left with 24 men and women, ages 18 to 55, who were overweight or obese and generally inactive. They invited everyone to visit the lab first thing in the morning, gave them breakfast, and on different days made them sit in silence, walk briskly on a treadmill, or lift weights for about 45 minutes.
Before, during and three hours later, researchers drew blood to check for changes in hormones related to appetite and asked the people if they were hungry. They also let them help themselves to a buffet of lasagna, salad, rolls, soda and strawberry cake, while discreetly monitoring the amount of food people ate.
So the researchers compared hormones, hunger and real food and found strange disconnects. In general, people’s hormones changed after each exercise session in a way that could reduce their appetite. But study participants did not report feeling less hungry — nor did they report feeling hungrier — after their workouts compared to when they were sitting down. And for lunch, they ate about the same amount, about 950 calories of lasagna and other buffet foods, regardless of whether they exercised or not.
The ‘lasagna flavor’ factor
The conclusion of these results suggests that at least a brisk walk or light weight lifting may not affect our subsequent eating as much as “other factors” such as the delicious aroma and flavors of a lasagna (bread rolls or pie), Tanya said. Halliday, assistant professor of health and kinesiology at the University of Utah, who led the new study. People’s appetite hormones may have dropped a bit after training, but that drop didn’t have much of an effect on how much they ate afterwards.
Even so, exercise does burn some calories, she said — about 300 each session. That was less than the nearly 1,000 calories the volunteers consumed on average at lunch, but hundreds more than when they were sitting down. Over time, that difference can help with weight control, she said.
Of course, the study has obvious limitations. He analyzed a single session of moderate and brief exercise with a few dozen participants out of shape. People who exercise regularly or who engage in more strenuous exercise may react differently. Researchers will need to carry out more studies, including with more diverse groups and taking place over a longer period of time.
But even now, the discoveries have the smooth charm of an apple pie. They suggest that “people shouldn’t be afraid to eat more if they exercise,” Halliday said. And, she said, a holiday indulgence won’t affect your weight in the long run. So, eat whatever you want at your feast and enjoy. Halliday also recommended a walk or some other physical activity with your family and friends first, if you can—not to curb your appetite, but to strengthen your social bonds and say thank you for moving forward together.
TRANSLATION LÍVIA BUELONI GONÇALVES