A magic calorie ride

Overeating, studies show, is fuelled by the same brain mechanisms that drive addiction to drugs like heroin

A magic calorie ride

Overeating, scientists say, may make people behave more impulsively | Gabriele Galimberti/Anzenberger; Hector Vivas/Getty Images

Bob, an office supervisor in Toronto, considers himself an addict. But the substance he’s prone to abusing isn’t drugs or alcohol—it’s food. “I would gorge on Raisinets, pizza, anything that I could get in quantity,” says Bob, 60, who asked that his last name not be used. He ran up a $4,000 Visa bill, almost all of it on food. Eating as a stress release, “I averaged about 15,000 calories a day.” He weighed 336 lb. at his heaviest. “I’m no scientist, but I think it’s an addiction,” he says. “When I read about how a drug addict behaves, my response is the same to food.”

The term “food addiction” is controversial, but recent studies have shown that high-calorie foods engage the same regions of the brain as drugs like heroin and cocaine. Over time, scientists say, a high-fat diet can impair the brain’s pleasure centres like those drugs do, encouraging ever-larger binges and making it harder to quit. Remarkably, a mother’s diet might even hard-wire her baby for obesity later on in life. “It’s too early to call it food addiction,” says Teresa Reyes of the University of Pennsylvania School of Medicine, who studies how the brain adapts to changes in diet. “But there is absolutely increasing evidence showing that the brain responds to high-sucrose, high-fat diets in a very similar way that it responds to drugs of abuse.”

At the Society for Neuroscience’s annual conference in November, Reyes presented her latest work: mice that were fed a high-fat diet for a long period of time, she found, showed changes in parts of their brains associated with pleasure and reward. Just like cocaine or heroin, unhealthy foods seem to trigger the brain’s pleasure centres, eventually desensitizing them. It becomes a vicious cycle. “To reach the same level of reward, the person needs to eat more rewarding food,” Reyes says. “It’s very similar to what happens in chronic drug abuse.” (This data is now under review before publication.)

Overeating, it seems, might also spark certain changes in the brain that make people behave more impulsively. Yale University’s Dana Small and Eric Stice of the Oregon Research Institute looked into this by feeding subjects a milkshake and checking on their brain activity using functional magnetic resonance imaging. Overweight and obese people, they found, had less activity in a part of the brain called the caudate nucleus (which is linked to impulsivity) than normal-weight people. This effect was especially strong in adults with a genetic variation that puts them at a higher risk of becoming obese.

In a separate study to be published later this year, Small and Stice found that kids who had two obese parents and were thus at risk of obesity had an increased caudate response. That surprising result suggests the adults’ dimmed reaction “is a consequence of overeating, rather than a cause,” says Small, who’s originally from Victoria.

Once someone starts regularly gorging on high-fat, high-sugar foods, a rewiring of the brain seems to occur. In March, researchers Paul Kenny and Paul Johnson published an influential study in the journal Nature Neuroscience showing, for the first time, that the same molecular mechanisms that influence drug addiction can fuel the urge to overeat. The two researchers provided lab rats with all sorts of unhealthy foods—like “cheesecake, bacon, sausage, and chocolate icing,” says Kenny, a drug addiction expert at the Scripps Research Institute in Florida—on a limited, or an unlimited, basis. (A separate group of rats had no access to junk food.)

Rats also had healthy food available to them, but opted for junk whenever it was provided. When fatty foods were taken away, “the obese animals basically starved themselves for days on end, rather than eat the regular food,” Kenny says. The animals’ brain reward circuitries were actually impaired, they found. Whether these pathways can ever change back again to respond more normally remains an open question.

Exactly when that change begins is still a question, too—although there are suggestions that a mother’s diet can predispose a child to obesity. In October, Reyes published a study looking at the effects of a mom’s diet on her offspring, feeding mother mice a high-fat diet throughout their pregnancy and lactation. They found “persistent changes in the brain chemistry” of their offspring, she notes, who “showed a stronger preference for higher-sucrose and higher-fat foods.” Changes persisted into adulthood. Sebastien Bouret of the University of Southern California has reached similar conclusions. “If you look at the brains of mouse babies born to obese mothers,” he says, “they have differences in the wiring of brain regions critical for appetite regulation.” Bouret looks specifically at a part of the brain called the hypothalamus, which regulates body weight. Maternal overnutrition or malnutrition can affect its development, he says.

Understanding how changes in the brain can drive overeating, Reyes says, might help create a better understanding of obesity in general, and “how difficult that cycle is to break.” Dr. Valerie Taylor, director of McMaster University’s Bariatric Surgery Psychiatry Program and mental health chair of the Canadian Obesity Network, agrees that the message around obesity needs to change. “Weight loss is rarely just a matter of eating less and exercising more,” she says, noting that obesity has strong links to mental health. The U.S. Food and Drug Administration is now looking at approving an obesity drug called Contrave—it would be the first new diet pill in a decade—that’s a “combination of an antidepressant, and [a drug] used to treat substance abuse,” Taylor says.

In December 2009, Taylor co-authored a commentary in the Canadian Medical Association Journal on the role of addiction in the obesity epidemic, noting many similarities between compulsive overeating and drug abuse. “Both food and drugs induce tolerance over time,” it says. “Withdrawal symptoms often occur. There is also a high incidence of relapse with both types of behaviour.” And, unlike some illegal substances, food is relatively cheap and easy to get. The commentary stopped short of calling frequent food-bingeing an “addiction,” but Taylor notes that the scientific evidence is getting stronger all the time, causing people in the field to rethink their stance on the subject.

Even so, blaming the obesity epidemic on a pattern of addiction similar to drug abuse is “preliminary,” says Dr. Yoni Freedhoff, medical director of the Bariatric Medical Institute in Ottawa, adding that more research needs to be done in humans. “The one thing that has changed very dramatically is the environment we live in,” he says. “That’s where I lay blame.”

As for Bob, he says he eventually learned to manage his urges to compulsively gorge on food—after joining Overeaters Anonymous, a worldwide support group modelled after addiction programs like Alcoholics Anonymous. (OA, which has been active in Toronto for over 30 years, has a 12-step program.) He’s been attending meetings for 28 years. “They keep you honest,” he says. “It’s not a sprint, it’s a marathon, and it’s something you deal with one day at a time.” Even after almost 30 years, “there are still temptations all over the place,” he says. At times, it can be “frighteningly difficult.” Today, Bob’s weight is stable at 168 lb.

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