MYTH: Exercise fuels appetite and causes dietary lapses.
THE TRUTH: Although findings are mixed as to whether people eat more when they exercise, a new study of 130 adults who were overweight or obese and were participating in a behavioral weight loss program showed that for every additional 10 minutes of total physical activity, the risk of a dietary lapse decreased by 1%.
Reduced-calorie diets can help people lose weight, but most do not stick to their diets 100% of the time, and lapses can sabotage their goals. Researchers at the WELL Center at Drexel University in Philadelphia wanted to understand which factors increase the risk of dietary lapses and wondered whether physical activity was truly one of the culprits.
“Physical activity is a particularly interesting risk factor,” said clinical psychology doctoral student Rebecca Crochiere, lead author of the study, “because experts disagree as to whether it increases risk or protects against subsequent overeating, which
inspired us to investigate its effect on dietary lapses.” Crochiere explained that some previous studies only included people of healthy weight who, relative to people who are overweight or obese, have been shown to have different appetitive responses to exercise. For example, people with obesity report reduced fullness following exercise versus no exercise, whereas people of healthy weight do not, Crochiere said.
Unlike previous studies, which focused on high-intensity exercise in a laboratory setting only, this study showed that exercises done outside of a lab and varying in intensity and duration affected appetite, fullness, and food choices. A recent review found low levels of exercise lead to appetite dysregulation and overconsumption, whereas high levels of exercise enhance the drive to eat but also increase the feeling of fullness after a meal, resulting in more regulated food intake (Physiol Behav. 2018;192:23–29).
Additionally, in laboratory-based studies, the researcher determines the intensity and duration of exercise, and participants may alter their eating behavior to please the researcher or in reaction to being watched or measured.
“These results may not be accurate representations for the real-world relations between exercise and eating,” Crochiere said.
The current study used six months of data from a year-long randomized controlled trial of participants 18 to 70 years old with a BMI between 27 and 50 kg/m2. These participants, who had the ability to walk without assistance for two city blocks, had received a one-year, 25-session behavioral weight loss treatment that prescribed a reduced-calorie diet and graduated physical activity. (These data were used because the graduated physical activity prescription reached its maximum level of 250 moderate-to-vigorous physical activity minutes/week at that point.)
Researchers did not measure the exact type of exercise participants engaged in, but rather had them use a wearable fitness tracker that measures acceleration, and the intensity of that acceleration, which was coded as “light” or “moderate-to-vigorous”mphysical activity. In the original intervention, researchers often recommended brisk walking as a way to achieve moderate-to-vigorous physical activity. Dietary lapse was defined as eating or drinking likely to cause weight gain or prevent weight loss, specifically eating a larger portion than intended, eating at a time when one had not intended to eat, or eating an energy-dense food one had intended to avoid. Throughout the day, the researchers sent brief surveys to participants’ smartphones. One of the survey questions asked, “Since the last time you completed this survey, did you have a dietary lapse?”
Because lapses were self-reported, Crochiere said it remains unknown whether calories were actually decreased or increased following exercise, and this should be investigated further. Although the researchers did not investigate why physical activity seems to protect against overeating, Crochiere said other evidence suggests hormones released following exercise may reduce hunger and food intake. “Another potential explanation is that exercise boosts mood or self-esteem,” she said, “which then improves motivation to eat well or within one’s diet. It also may temporarily increase commitment to dietary goals because individuals do not want to undo the hard work they put into physical activity.”
Since most behavioral weight loss programs prescribe exercise for its health benefits and because it burns calories, these findings suggest that exercise may also aid in adhering to a reduced-calorie diet, perhaps through improved regulation of eating behavior.
“One more reason to recommend exercise if you are a physician,” Crochiere said, “and one more reason to engage in exercise if you are a patient seeking weight loss.”