"This study provides evidence that exercise not only affects energy output, but it also may affect how people respond to food cues," said Brigham Young University professor James LeCheminant in a university news release.
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In conducting the study, researchers led by Bliss Hanlon, a former BYU graduate student, measured the brain activity of 18 normal-weight women and 17 obese women as they looked at 120 pictures of food. Women were also shown 120 pictures of flowers to serve as a "control" or comparison.
The brain measurements were taken twice. The first assessment occurred one hour after the women walked briskly on a treadmill for 45 minutes. One week later, the researchers measured the women's brain activity again on a morning free of exercise. On both days, the women tracked their food intake and physical activity.
Women had less interest in food following a workout, the researchers found. They also noted the women did not eat more on the day they exercised to "make up" for the calories they burned.
"We wanted to see if obesity influenced food motivation, but it didn't," LeCheminant said. "However, it was clear that the exercise bout was playing a role in their neural responses to the pictures of food."
The researchers said that more research is needed to determine how long the reduction in motivation for food lasts following a workout, particularly if people engage in long-term exercise regimens.
The study was published online and in the October issue of Medicine & Science in Sports & Exercise.