Obese or Lean? How Your Brain Decides

Predestined to obesity by brain dopamine and your parents

Posted Mar 24, 2011

Are we born destined to become obese? Apparently yes.   A recent publication by scientists at the University of Buffalo and Yale in the Journal of Neuroscience offers some fascinating clues to which part of our brain is responsible.  This new knowledge may lead to more effective drug therapies to help obese children and adult lose weight. 

Fifteen year old adolescent males and females of normal weight were separated into two groups: those who were at high risk for future obesity and those who were at low risk for future obesity. What does it mean to be at high-risk for future obesity?  Many studies have shown that children who have two obese or overweight parents are four times more likely to become obese themselves.   To be considered low-risk the parents of the adolescents needed to be lean, i.e. a body mass index less than 25. When the children in the high risk group were shown pictures of tasty-looking, high calorie foods the pleasure centers in their brains became highly activated, especially as compared to the response of the same brain regions in the low risk children. The activation of these pleasure centers depends upon the function of the neurotransmitter called dopamine.   

This study demonstrated that in the brains of children born to obese or overweight parents, the neurotransmitter dopamine over-responds to the sight of tasty, high calorie foods.  The neurotransmitter dopamine is famous for being the brain's reward chemical.  Everything you do that brings pleasure somehow involves the action of dopamine in one of your brain's pleasure centers. For example, neuroscientists have shown that eating chocolate, feeling pleasure from the sight of a beautiful sunset, having sexual relations, or injecting heroin all lead to the activation of dopamine in the brain.  Thus, children who are destined to become obese apparently inherit a dopamine system that becomes a lot much more excited to the sight of a chocolate milkshake than does the dopamine system in the brain of a child who is not destined to become obese as an adult.  In a sense, these children are addicted to tasty, high calorie foods in the same manner that someone might become addicted to heroin or gambling.  In all cases, enhanced dopamine function in the brain is responsible.

The study also indicated that as these children mature and gain weight their hyper-responsive dopamine system actually tries to turn itself off.  Apparently, as a consequence of overeating the dopamine system of obese people becomes rather over-taxed and ultimately unresponsive to tasty looking foods.  As an adult, the lack of pleasure from eating these high calorie foods would then predispose them to eating ever greater quantities in an attempt to reinstate the pleasureable feelings these foods once produced in them.  Once again, the diet-induced changes taking place inside their brains would be quite similar to the adaption experienced by methamphetamine addicts who need to inject ever greater amounts of drug to reach the same high once achieved with much lower doses.  

The dopamine system in the brains of the obesity prone adolescents in this study also demonstrated another surprising behavior.   Apparently, not only were the dopamine neurons more responsive to tasty, high calorie foods but they were also more responsive to money.  Thus, some children might inherit a tendency to hyper-respond to virtually anything that is rewarding, such as food or money. 

Children who are destined to be obese also seem to have a more robust response in their brain to the unique sensory cues that distinguish fatty foods, such as the creaminess, viscosity and texture experienced by their tongue.  Thus the taste of a piece of milk chocolate actually turns on their brain more dramatically than it does in a child who is not destined to become obese as an adult. 

Fortunately, there are ways to block the specific actions of dopamine observed by these neuroscientists; the challenge will be to find a way to do this safely and effectively. 

© Gary L.Wenk, Ph.D., author of Your Brain on Food (Oxford, 2010)

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