Dieters often jokingly will refer to pizza or potato chips as "crack." They might be on to something.
New evidence suggests that over-indulging in high-calorie foods can, in fact, alter the brain in ways similar to drugs, contributing to the development of addiction-like compulsive eating.
In a recent study conducted by scientists at the Scripps Research Institute, Jupiter, Fla., and published in the journal "Nature Neuroscience," when rats raised on healthy food were suddenly given unrestricted access to a diet loaded with fat and sugar, they completely lost control over their eating. Even mild foot shocks couldn't keep them from compulsively consuming bacon, cheesecake, Ding Dongs and other highly palatable, readily available junk food. Within 40 days, their weight had increased 25 percent.
In addition to getting fatter, the rats developed the same changes in brain reward circuits that have been reported in humans addicted to drugs - specifically, they showed lower levels of the dopamine D2 receptor.
The brain releases bursts of dopamine in response to feel-good experiences, such as eating cookies or snorting cocaine. However, scientists believe that too much of a "good" thing can overload and essentially crash the dopamine D2 receptor, making it necessary to take more drugs, or, in the case of the rats, eat more and more to achieve the same pleasurable effect.
The resulting lowered D2 receptor levels then seemed to drive the development of "habitual" feeding behaviors among the rats, says study co-author Paul Kenny, PhD, an associate professor at Scripps. To wit, when researchers replaced the junk food with healthy fare, the animals opted to starve themselves.
So, what implications might the study's findings have for humans?
First, once the D2 receptor levels have plummeted, banishing bad-for-you food from a diet may be more difficult than just saying no.
"We're not sure precisely what's regulating everything, but the effect on human D2 receptors appears to last for months after a person stops eating heavily," Kenny says. "They may be able to normalize somewhat, but they will have this very long lasting period of vulnerability to re-engaging in the behavior."
Further, any excessive weight from these poor eating habits may actually serve to perpetuate the problem.
"When people who are overweight undergo bariatric surgery, their D2 receptor levels begin to increase as they lose weight," Kenny says. "We suspect that circling signals from the periphery of the body are actually influencing the receptor levels in the center of the brain."
In other words, eating junk food just makes you want more junk food, which can make you gain weight, which, in turn, lowers your D2 levels and further fuels your addiction to junk food.
Although Kenny is interested in exploring how drugs that help treat substance abuse may also be effective for overeating, it seems like the best solution is to avoid getting stuck in this vicious cycle in the first place.
But, as the Scripps study exemplifies, simply quitting bad eating habits cold turkey isn't easy, says Elisa Zied, a registered dietician and author of "Nutrition At Your Fingertips" (Alpha, 2009).
Instead, the best way to permanently alter behavior is by taking the gradual approach, she says. "This can minimize feelings of deprivation and help you adapt physically and mentally to your new, more healthful habits."
To get started, here are Zied's top five ways to start weaning junk from a diet:
1. Stop buying "trigger" foods that are irresistible even when hunger isn't an issue.
2. Fill the fridge and pantry with nutrient-dense foods, such as fresh fruit and veggies, whole grains, low-fat/no sugar-added dairy foods and lean protein. Put produce in an accessible place so it will be eaten first.
3. Buy small portions of treats, but keep them out of sight in a cabinet or pantry or on a high shelf.
4. Practice portion control. Limit treats to no more than 100-150 calories per day max, leaving more room calorie-wise for foods/beverages from the healthy food groups.
5. When indulging in a treat, do so while sitting down and not distracted. "Taste and savor the treat," Zied says. "Your body - and brain - will thank you!"