High-Calorie Food Triggers Addiction-Like Responses

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For some, dieting is a difficult undertaking because food seems to “call to you”, destroying your willpower to eat healthful foods in order to lose weight. A new study from researchers at the Scripps Research Institute in Florida say that feeling may just be in your head – literally.

Researcher Paul Kenny and colleagues found that high-calorie foods triggered an addiction-like response in the brains of laboratory rats, and that the foods may lead the animals into becoming compulsive eaters.

While the findings may not be able to be directly applied to the increasing trend of human obesity, it may help in the understanding of the condition and in developing therapies to treat it. Kenny said, “Obesity may be a form of compulsive eating. Other treatments in development for other forms of compulsion, for example, drug addiction, may be very useful for the treatment of obesity.”

The researchers divided the rats into three groups. One group ate a balanced healthy diet. Another received healthy food, but had access to high fat, high calorie foods such as snack cakes, bacon, desserts, etc. for one hour a day. The third group was fed a healthy diet, but had unlimited access to the unhealthy food. All of the rats had also been trained to experience a minor shock when exposed to a light.

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During 40-day study, the rats in the third group developed a preference for the high-calorie food and shunned the more healthful food in order to eat it. The rats ate about twice as many calories as the control rats and quickly became obese. These rats also learned not to respond to the danger of the light, and instead ate the snacks, in spite of the pain of the shocks. This is indicative of compulsive eating.

The study also found that when the “junk food” rats were put on a more nutritious diet, they simply refused to eat. Kenny says that they basically starved themselves for two weeks.

The rats in the second group also displayed actions similar to compulsive eating. When offered the unhealthful food for one hour, the researchers found that those rats managed on average to consume 66% of their daily calories in 60 minutes – a symptom of compulsive binge eating.

The scientists found decreased levels of the dopamine D2 receptor in the overweight rats. The D2 receptor responds to dopamine, a neurotransmitter released in the brain during a pleasurable experience. This same effect has been seen in humans that are addicted to drugs, such as cocaine or heroin. This overloads the brain’s “pleasure centers”, and eventually a person needs more and more to achieve the same level of satisfaction.

"The new study… explains what happens in the brain of these animals when they have easy access to high-calorie, high-fat food," said Kenny. "It presents the most thorough and compelling evidence that drug addiction and obesity are based on the same underlying neurobiological mechanisms. In the study, the animals completely lost control over their eating behavior, the primary hallmark of addiction. They continued to overeat even when they anticipated receiving electric shocks, highlighting just how motivated they were to consume the palatable food."

Journal Reference:
Paul M Johnson, Paul J Kenny. Dopamine D2 receptors in addiction-like reward dysfunction and compulsive eating in obese rats. Nature Neuroscience, 2010; DOI: 10.1038/nn.2519

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