Nutritionists at Aberdeen University used brain imaging to discover a new link between exercise and appetite.
Participants in the study were found to be more likely to choose healthy options such as fruit and vegetables after running fast for an hour.
It is hoped the findings will help the understanding of how exercise can be used to tackle obesity.
Dr Daniel Crabtree, from the university's Rowett Institute of Nutrition and Health, said: "The key aim of our research was to examine the brain's responses to high and low-calorie food following a period of acute exercise."
The findings, published in the American Journal of Clinical Nutrition, may be related to greater thirst levels after exercise and the perception of low-calorie foods having greater water content, Dr Crabtree said.