Are obese people obese because they eat too much, metabolize slowly, or both? Most studies show that overeating is the major factor, but what is the neuroscientific basis for this?

One of the leading hypotheses comes from studies on rats, and claims that blunted pleasure circuits in the brain result in overeating. Obesity-prone rats have a significantly lowered baseline level of dopamine and level of dopamine release. The practical result is that obesity-prone rats have to eat more to achieve the same pleasure from food as obesity-resistant rats can.

What about humans though? Do obese people have less dopamine release in their brain in response to food than thin people do? A study from the Oregon Research Institute conducted functional magnetic resonance imaging studies (brain scans) on young women, scanning their brains while they received chocolate milkshakes through syringe pumps. They found that the obese women showed blunted dorsal striatum responses to the food reward, likely prompting them to compensate for the blunted reward by overeating.

This sort of basic research into the pleasure circuits of the brain provides hope for conquering this enormous health problem that’s sweeping over the world, especially the United States.