The runner tethered to the treadmill and the couch potato gripping a bag of chips may seem like polar opposites, but new research suggests that a single alteration in the brain’s reward system could cause both obsessions.
More than one third of regular gym-goers show signs of exercise dependence, continuing to exercise even when sick or injured or arranging their lives around working out. Nearly half of all people diagnosed with an eating disorder report excessive levels of exercise to control body shape and weight and to relieve stress and improve mood. Researchers have developed two opposing hypotheses to explain how someone could become addicted to exercise, eating or any other behavior. The first hypothesis states that these people’s brains grow more sensitive to reward; they find exercise more pleasurable, so they seek it more. Alternatively, these individuals may grow less sensitive to reward; over time they begin to require more exercise to achieve the same level of pleasure.
A new study, led by Wendy Mathes of the University of North Carolina at Chapel Hill, found that two strains of mice, bred for either excessive exercise or obesity, had the same malfunction in the brain’s reward pathways. Genetic analysis of the two kinds of mice showed that they had lower-than-normal levels of activity in a gene that helps brain cells register the presence of dopamine, the neurotransmitter involved in reward. The finding suggests that excessively exercising mice and obese mice may be less sensitive to the rewards of physical activity and food, respectively. Researchers do not know yet how the same underlying problem could lead to such radically different outcomes, but Mathes suggests that other neurotransmitters may act on the dopamine-deprived brain cells to push the mice in one direction or the other.
This article was originally published with the title Two Sides of the Same Coin.
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4 Comments
Add Commentgood grief... its easy. dopamine makes you feel good. exercising and over eating provide that in us that don't have enough....
Reply | Report Abuse | Link to thisThis is funny, and startlingly accurate. I used to be a 'gym-bot' planning my time around the schedule of my dojo. Eating was something I did so I could get back quickly. After my hip injury I was laid up for a while and learned how to cook. I started enjoying food and put on a lot of weight. Same thing seems to happen to a lot of athletes who suddenly stop playing.
Reply | Report Abuse | Link to thisWhile many people may perceive that their activities reduce stress, it may be more accurately said that they pursue their activities in response to stress. As I understand, addictive behavior produces generally increased stress as activities becomes less effective at reducing stress.
Reply | Report Abuse | Link to thisI expect that Scientific America would be more rigorous and exact than to equate obesity with sloth and/or binge eating disorder.
Reply | Report Abuse | Link to thisObesity is not an addiction, nor is it evidence of an addiction. Would you presume that a thin body was a de facto sign of gym addiction?
This is sloppy thinking and unworthy of Scientific America--or anyone claiming to talk science.