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Why Is Obesity So Hard to Defeat?

Constantly bathing the brain in fat changes its DNA.

We are all well aware that eating diets high in fat and sugar will lead to obesity. Somehow, the solution should be just as easy: stop eating fat and sugar. Yet, for obese people, fat and sugar are craved like heroin or methamphetamine: Why? The answer is that these diets actually change how the brain functions.

Day after day, year after year, the constant bathing of the brain and body in fats and sugar slowly changes how the DNA in the cells of our brain's feeding center behaves. Due these gradual modifications in gene function, our brain circuitry changes; ultimately, it rewires itself to crave these foods. The pattern of our eating changes so that we eventually eat more every day in order to feed this ever-more-powerful new software program that is evolving inside our brain.

Initially, scientists assumed that obese people were simply addicted to food in the same manner that someone becomes addicted to heroin, i.e. food produces happy pleasant feels, and therefore eating lots of food would produce extremely pleasant feelings. Not so. A few years ago scientists discovered just the opposite was true; the brain's reward center decreased its response to eating tasty foods. This induces people (and animals in experimental studies as well) to consume ever greater quantities of fat and sugar in order to mitigate the diminished rewards that were once experienced by consuming only one scoop of ice cream or a small donut.

The neurotransmitter in the brain for rewarding us for eating is called dopamine. Everything we do that is pleasurable requires the release of dopamine within the brain. Dopamine within our feeding centers induces us to eat and rewards us for doing so. Needless to say, eating fat and sugar induces the release of dopamine. In both obese humans and animals dopamine function is significantly impaired. The key thing to point out is that this dysfunction occurs in response to many years of poor diet; dopamine dysfunction does not occur first. Our behavior leads to the dysfunction in this important pleasure-inducing neurotransmitter.

A recent study published in the Journal of Neurochemistry reported that dopamine's normal function is enhanced in the feeding centers, leading to increased craving for high calorie foods, while its function is decreased in our reward centers, leading to a decrease in the pleasure that obese people can derive from eating tasty foods. Thus, ultimately, obese people are driven to eat more but enjoy it much less. The main value of this recent study is that it offers hope that one day it might be possible to correct this dopamine dysfunction with medication.

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

See also: Why Marijuana and Coffee Are Good for the Brain