Brain vs. Food
Fueling for exercise, especially during long runs, is a commonly discussed topic in the running world. Pre-race carb-loading, mid-race fuel sources, and post-race meals are all part of a typical routine. So why do we sometimes not feel hungry when finishing a run? And why are we starving other times? It turns out that following aerobic exercise our brain’s response to food can sometimes be reduced.
Previous studies have shown that exercise decreases appetite due to suppressed release of appetite-stimulating hormones or altered body temperature, decreased stomach activity, and dehydration. This study wanted to examine if exercise would change the neuronal (brain) response to visual food cues. Thirty healthy and active adults who are capable of performing 60 minutes of bike exercise were recruited for this study. All subjects had no contraindications to undergoing an MRI or current injury.
Each subject fasted for 8-12 hours overnight and answered an appetite questionnaire prior to testing. Participants then either exercised for 60 minutes on a bike or rested. Immediately after, each person went into an MRI machine, in which pictures of high and low energy foods such as french fries, ice cream, fruits and vegetables were displayed on a monitor, alongside control pictures of trees and flowers. The functional MRI looked at what areas of the brain were used when looking at each picture.
Interestingly, the study found that exercise reduced the response of the brain in areas associated with food reward, control of food behavior, and pleasantness of food. While participants were not given actual food, their brain response to food cues was decreased. The response may have been different if other sensations were tested such as smell and taste. This study had some limitations. It did not assess body temperature and weight following exercise, which has also been shown to decrease appetite.
Additionally, the authors also did not measure energy expenditure, which can also alter appetite. As runners we need to ensure that we place as much emphasis on our post-run nutrition as we place on the pre-run meal. Even if you aren’t feeling hungry, grab something light, like a banana. You body needs nutrients to recover from your run and help prepare for your next one!
Evero, N., Hackett, L. C., Clark, R. D., Phelan, S., & Hagobian, T. A. (2012). Aerobic exercise reduces neuronal responses in food reward brain regions. Journal of Applied Physiology,112(9), 1612-1619. doi: 10.1152/japplphysiol.01365.2011
Lisbeth Hoyt, DPT