Why We Crave Sweets and Fats

How is candy like cocaine?

There’s a steadily growing body of research that says that foods high in sugar and fat—all those forbidden yummies like candy, cookies, cheesecake, and pizza—may lead to food addiction. Food addiction is potentially a painfully real disease akin to drug addiction and alcoholism. Processed foods, according to a recent study from the University of Michigan, have the same effect on the brain’s reward centers as hard drugs. This may be why you ate the entire bowl of Halloween candy this weekend.

The Michigan study is just the tip of the iceberg of food addiction research, a body of knowledge that has been steadily accumulating over the past decade. In a 2010 article in the journal Nature Neuroscience, for example, scientists found that rats, fed on bacon, pound cake, cheesecake, and frosting became so hooked on their sinful diet that they continued chowing down even in the face of punitive electrical shocks. Further investigations showed that the brains of the cheesecake-scarfing rats looked much like those of drug addicts and alcoholics.

The pleasure center of the brain is formally known as the nucleus accumbens, a clump of nerve cells tucked beneath the cerebral cortex. When a rat—or a human being—gobbles a Twinkie, downs a martini, or takes a hit of a narcotic, the nucleus accumbens is doused with dopamine, a neurotransmitter that sends a feel-good message to the body. Too much dopamine, however, and the reward system becomes overwhelmed and starts to shut down, primarily by reducing the number of cell-surface receptors for dopamine. A steady dose of drugs, alcohol, and some foods, in other words, can literally change the structure of the brain.

When dopamine receptor levels drop, more and more of a reward-generating substance—say, candy—has to be consumed in order for the brain to register the same degree of satisfaction and pleasure. This mechanism underlies drug and alcohol addiction, and researchers are becoming increasingly convinced that it also plays a role in compulsive junk-food eating and obesity.

Witness rats on Oreos. Psychologist Joseph Schroeder, director of the behavioral neuroscience program at Connecticut College, and his students compared rats fed on Oreo cookies to rats fed on rice cakes using a behavioral model called conditioned place preference – which, in layperson’s terms, means that rats prefer to hang out in places where good things have happened. Rats given injections of morphine or cocaine, for example, much preferred to spend time in the narcotic-dispensing drug room area of their cage rather than in the boring control room, where they were treated with doses of saline.

Similarly, rats fed on Oreos gravitated to the Oreo room, while flatly spurning the nutritious but blah rice-cake room. (Adorably, rats, like people, prefer to eat their Oreos by peeling them apart and eating the filling first.)

Even more tellingly, however, the brains of the Oreo-eating rats were found to be high in a protein called c-Fos, a marker of nerve-cell activity, in the nucleus accumbens, the brain’s pleasure center. In fact, in the rats, even more pleasure-center nerve cells were activated in response to Oreos than in response to cocaine or morphine. The conclusion was that high-fat/high-sugar foods may be habit-forming.

New York’s pizza-snatching Pizza Rat isn’t just scavenging. He’s hooked.

And it’s not just rats. Ashley Gearhardt, working with Kelly Brownell and colleagues at Yale University, identified potential human food addicts by means of a 25-question survey, then used magnetic resonance imagery (MRI) to record their brain activity in response to food. Results showed that pictures of milkshakes caused the pleasure centers of the subjects’ brains to light up, much like the MRI responses of alcoholics anticipating a stiff shot of booze.

Results were even more compelling when test subjects were actually allowed to drink their milkshakes. In one study, overweight or obese men were given either low- or high-sugar milkshakes, cleverly matched for sweetness, texture, and caloric content. Taste-wise, the shakes were identical—but their effect on the brain was a whole different ballgame. While the low-sugar drinkers showed little pleasure-center effect, the nucleus accumbens of participants who drank the high-sugar shakes lit up like Christmas trees. Furthermore, high-sugar shake consumers, four hours later, reported hunger pangs and cravings for more.

Some scientists point out the “addiction” is too strong a term for our brain’s response to high-sugar/high-fat food. After all, nobody’s knocking over the local 7-11 because they’re desperate for a bag of Oreos or a quart of Cherry Garcia ice cream.

For struggling weight watchers, however, such research indicates that obesity may be less the result of weak will and self-indulgence than of brain chemistry. It may be time to view our national obesity epidemic in a whole different way.

Are You Addicted to Food? Take the quiz.

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