Scientists shouldn’t get hooked on notion that obesity reflects addiction to food

One of the most chilling newcomers on the addiction scene is dirt cheap and easy to score.

Known on the street as “Scream,” “Brain Freeze” and “Chunky Monkey,” this high is easy to ride — all it takes is $4 and a visit to your local grocer’s freezer section. You’ve probably encountered — and maybe even used — this latest menace yourself: ice cream.

Breathless media reports likening ice cream to cocaine were spawned by a recent study. Brains of habitual ice cream eaters showed blunted responses to milk shakes compared with people who rarely indulged. Like cocaine users forced to keep upping the dose to get that good feeling, these shake addicts, the reasoning went, developed tolerance to their drug. Once an emblem of wholesomeness, ice cream has been smeared.

Ice cream isn’t alone in its sullied reputation. It has joined love, gambling, porn, Facebook and cupcakes on a growing list of substances claimed to be as addictive as cocaine. But the correct list of substances as addictive as cocaine, as British psychologist Vaughan Bell points out on his blog Mind Hacks, includes just one: cocaine.

This deliciously snarky complaint feeds into a larger point — that scientists (and the media) have been swept up in an addiction frenzy, on high alert for the next big addictive substance. And for a growing number of people, that next big thing is food.

Talking about overeating and obesity in addiction terms is appealing. At a basic level, it makes sense. Anyone bold enough to hungry-drive past an In-N-Out Burger knows that the smell of an animal-style cheeseburger incites a powerful craving. (My personal solution: I don’t inhale.)

In many ways, the brain’s responses to junk food and addictive drugs look awfully similar, various studies have reported. In addition to craving and tolerance, overeating is accompanied by other classic addiction hallmarks: an inability to quit, withdrawal and using the substance despite knowing the bad consequences.

These similarities — both in the brain and in the behavior — have sparked a shift in how neuro­scientists talk about food. Fueled in part by this addiction theory, some scientists have even made the case that obesity should be included in DSM-V, the next version of the psychiatry diagnosis bible.

But just because things appear similar doesn’t mean they’re the same. Results from human brain scan studies are equivocal on the issue, psychiatrist Paul Fletcher of the University of Cambridge and his colleagues write in Nature Reviews Neuroscience. The pattern emerging from brain-scanning studies on obese people and binge eaters is “most remarkable for its variability and inconsistency,” the team writes.

By far, the best evidence for food as an addiction comes from rodent studies, Fletcher says. But those studies have problems. Translating results from a junk food–junkie rat to a person is like reading a nutrition label written in Egyptian hieroglyphics.

As these cautionary notes suggest, the addicted-to-food theory may be enjoying a supersized influence. People ought to think carefully before scooping ice cream into the same dish as truly dangerous and addictive drugs. By locking in too early to this addiction framework, to the exclusion of other viewpoints, scientists could miss some really important features of obesity. It’s just too soon to say that the addiction idea is right.

And of course, it is too soon to say that the addiction idea is wrong. Thinking about obesity in those terms actually might help scientists explain and treat a particular aspect of overeating, or overeating in a subset of obese people. Obese people with binge eating disorders, for instance, might show more addictive features than people with more common forms of obesity.

By its very nature, food is different from drugs. People can live without cigarettes, heroin and cocaine, but not without food. Our intimate relationship with food is shaped by our requirement for it. And the brain controls this relationship every minute — making choices about which foods to eat, how much, and when, in lots of nuanced, complicated ways.

A huge range of factors can nudge our brains to make good or bad food decisions. Genetic factors, social pressures, jobs that require hours of inactivity, an abundance of cheap, nutritionally poor food and, as my colleague Nathan Seppa just pointed out, a lack of nearby grocery stores stocked with fresh food.

Understanding how the brain navigates these pressures will probably require a smorgasbord of diverse hypotheses and experiments. And the overeating-addiction idea may turn out to be one of the better ones. But until the data are in, it’s best to keep all the options on the table. After all, the slogan that allows me to eat my scoops of Rocky Road free of guilt also applies to the scientists studying why I crave it: Moderation is the key to success.

SN Prime | May 28 – June 4, 2012 | Vol. 2, No. 22

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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