“It’s this wanting that seems to drive food addiction,” says Gearhardt. In a recent study, she used functional MRI scans (which measure blood flow in the brain) to demonstrate that when food addicts see images of chocolate milk shakes, they have a lot more activity in the brain regions associated with dopamine release than nonaddicts do. “When food addicts get food cues, they likely experience a big dopamine burst in their brains, and that encourages them to want the food more than nonaddicts do,” she says. “Seeing a McDonald’s, for instance, would prompt them to go in even if they’d been thinking about eating healthfully and staying on track just five minutes earlier.” And as we all know, these kinds of cues abound in the United States. “Our environment is filled with readily available, inexpensive, high-calorie, irresistible foods,” notes Joe Frascella, PhD, director of the division of clinical neuroscience and behavioral research at the National Institute on Drug Abuse.
Food-addiction researchers have been studying a particular brain receptor, called the D2 receptor, that responds to dopamine. Our brains are constantly making D2 receptors, but overeating or overconsuming alcohol or drugs interferes with the maturation process of these receptors. As a result, people who are obese or addicted to alcohol or drugs have fewer functioning D2 receptors. And these low levels can lead to all kinds of compulsive behavior, including eating, that are intended to punch up the reward system in the brain.
Kenny’s team at Scripps did an experiment in which it lowered rats’ working D2-receptor levels, then fed them rich food. As soon as the rodents had a taste, they began eating compulsively. More important, they wouldn’t stop—even when threatened. (The researchers had trained the animals to associate a flashing light with a foot shock.) “When the control animals saw the light, they stopped eating because they anticipated danger,” explains Kenny. “But the rats with fewer functioning D2 receptors were so motivated to eat, they ignored the possible negative consequences.” Kenny likens this behavior to that of a crack addict who’s lighting up while the police are banging on the door. “Getting your fix is so important, you can’t stop, and that seems to be the case with these animals with less D2 receptors, even before they became obese,” he says.
Inability to stop is what sets food addicts apart from people who simply enjoy eating and have the love handles and belly pooch to show for it. Food addicts generally don’t savor their food; they devour it. Even when it’s not particularly tasty. Even when they feel full. Still, their personal chemistry prompts them to continue to eat. Compared with those less hooked on food, addicts show far less activity in the lateral orbital frontal cortex, the brain region that tells you when to stop eating. “With food addicts, their brakes don’t work, so they lose control of their consumption,” says Gearhardt.
Here’s where your genes come in: Research says the people most at risk for food addiction are those who already have lower levels of working D2 receptors because there’s some kind of compulsion in their family background. Booze, drugs, sex, porn, shopping, gambling—it doesn’t matter what; the reward circuitry responds the same way. However, your family is only part of the story. “Even without a genetic head start, if you ultimately keep eating highly palatable food, you’re at greater risk of becoming a compulsive eater,” warns Kenny. In other words, your eating behavior can lead to addiction-creating changes in your receptors.
Kicking Your Addiction
Go to any kind of 12-step meeting, and you’ll hear the same mantra: Don’t pick it up. Don’t touch the booze, the crack, the cards, the cupcakes. Because as any reputable program will tell you, the only way to break an addiction is abstinence. Break the addiction, and your number of fully functioning D2 receptors will increase. But when the addiction is to food, you can’t go cold turkey, because, um, you still need to eat.