The idea that you can "work up an appetite" by doing a vigorous workout turns out not to be true, say researchers from Brigham Young University. Their study, in the journal Medicine & Science in Sports & Exercise, shows that 45 minutes of moderate-to-vigorous exercise in the morning actually reduces a person's motivation for food.
For the study, researchers James LeCheminant and Michael Larson measured the neural activity of 35 women (some obese and some normal weight) while they viewed food images, both following a morning of exercise and a morning without exercise. The exercise consisted of walking on a treadmill for 45 minutes.
The researchers found the subjects' attentional response to the food pictures decreased after the brisk workout. "This study provides evidence that exercise not only affects energy output, but it also may affect how people respond to food cues," LeCheminant said.
Interestingly, the 45-minute exercise bout not only produced lower brain responses to the food images, but also resulted in an increase in total physical activity that day, regardless of the subject's body mass index.
"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."
Larson added that researchers still need to determine how long the diminished food motivation lasts after exercise and to what extent it persists with consistent, long-term exercise. "The subject of food motivation and weight loss is so complex," Larson said. "There are many things that influence eating and exercise is just one element."
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Source: Brigham Young University