Winter 2015

The Dope on Dopamine

And why it makes it hard to diet

By Jacqueline Mitchell

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“Even though they are mirror opposites, the undernourished and the obese share two things—an increased motivation to eat and a deficient brain dopamine system,” says Emmanuel Pothos. Illustration: Roger Harris/Science Source

Why is it so difficult to eat less?

That’s what Emmanuel N. Pothos, Ph.D., an associate professor of pharmacology and experimental therapeutics and of neuroscience in Tufts School of Medicine’s Department of Integrative Physiology and Pathobiology, and his colleagues are trying to understand. Pothos’ research focuses on the reward system in the brain that makes us want food. As it turns out, this system depends heavily on the chemical dopamine, normally released when an animal eats a meal. Dopamine produces a pleasurable sensation that lets the animal know it has satisfied a primal need.

Starvation, however, alters this otherwise tidy feedback loop. When an animal is having a hard time finding enough food, the brain doesn’t want it to feel satisfied after just one meal, so it releases less dopamine. Pothos and other researchers have seen corroborating evidence in the lab: The brains of underweight animals release less dopamine than those of normal-weight animals.

Oddly, the brains of overweight animals release less dopamine as well. And human brain imaging by other researchers indicates that something similar is likely going on in people. “Even though they are mirror opposites, the undernourished and the obese share two things—an increased motivation to eat and a deficient brain dopamine system,” Pothos says.

A number of factors can knock the reward system off kilter: genetic predisposition, the environment a baby encounters in the womb, gaining or losing weight and certain diseases, including addiction. Yet the situation, while difficult to correct, is not hopeless. Exercise may offer a solution—and not just because it can burn off calories. Pothos says there’s early evidence that regular exercise, in addition to all its other benefits, can help reset the dopamine reward system.

 

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The Dope on Dopamine

And why it makes it hard to diet