We like sweets and we like fats. That’s why we serve cheesecake for dessert instead of carrot sticks. Great for the taste buds but not for the waistline. And when the belt starts to become too tight, we try to forget the dessert. But some people just can’t. They have all the best intentions to shed those extra pounds, but they just can’t give up eating the sweetened fatty stuff. It is as if they were addicted to junk food. And they may well be, at least based on an interesting study carried out at the Scripps Research Institute in Florida. Let’s make something clear right off the bat here. The test subjects were rats, not people. And as with any other rodent study, extrapolation to humans may or may not be valid. Scripps neuroscientist Dr. Paul Kenny, like many researchers around the world, was interested in the vexing problem of weight control. Why do some people have such a difficult time controlling their food intake in the face of extensive publicity about the horrors of obesity? Could it be that their body chemistry has somehow gone awry? Could a rat feeding study possibly shed light on the situation?
Kenny fed one cohort of rats the usual rat chow while another group was allowed to feast on sausage, bacon and cheesecake to their heart’s delight. Actually their hearts probably were not delighted by the onslaught of fat, but that was not the point of this study. As one might expect, the rats on the fatty diet ballooned. All the animals were fitted with electrodes implanted in the brain designed to monitor the activity of their pleasure centers. No great surprise, the rats dining on the fat feast got a great deal of pleasure. Their brain neurons were pumping out more and more dopamine, a neurotransmitter associated with pleasure. Dopamine fits into so-called dopamine receptors, much like a key fits a lock. When the fit is right, pleasure is sensed. And then a strange thing happened. The rats’ nervous system reacted to the increased levels of dopamine by curbing the activity of the receptors. Sort of a protective physiological reaction to an abnormal level of dopamine activity. And what did the rats do in response? They ate more, their bodies subconsciously wanting to produce more dopamine to counter the poor receptor activity. Even subjecting the animals to electric shocks when they approached the food was not a deterrent. Now, that sure sounds like addiction! Indeed, the chemistry here is very similar to that of cocaine addiction. Cocaine increases the stimulating activity of dopamine, which in turn provides so much pleasure that people are unable to give up the drug. We are not talking about physiological addiction here, such as seen with heroin. In that case serious physical symptoms are associated with withdrawal of the drug. The cocaine or the junk food addictions are based on not wanting to give up the pleasure associated with the activity. This can be very powerfully addictive psychologically.
The researchers went on to prove their point by cleverly using a virus to down-regulate dopamine receptors in healthy normal weight rats and noting their increased appetite for junk foods. So what does this mean for humans? That the pleasure we get out of eating fatty foods can be addictive. Pastries, ice cream, pizza, hamburgers, French fries fall into that category of being dopamine releasers. Nobody talks about being addicted to broccoli, apples or oat bran. But luckily humans have something that rats don’t. A brain capable of making intelligent decisions. And the intelligent decision is to limit junk foods even if this presents a challenge.