The latest study, published March 28 in "Nature Neuroscience," likened the affects of high-fat, high-calorie fast food to those of cocaine or heroin, in animals at least.
The researchers showed that the pleasure-center in rats brains were overstimulated from the fast food similar to an addict's cocaine binge. Eventually, the pleasure centers became so overloaded that rats needed more and more food to feel normal, according to Paul H. Kenny, an associate professor of molecular therapeutics at the Scripps Research Institute.
Throughout the study, Kenny and his co-author studied three groups of lab rats for 40 days. The first group ate healthy food. The second ate a limited amount of junk food. The third group, however, was allowed to gorge on high-fat, high-calorie foods and became obese.
The startling side effect? The brains of the obese rats changed. "The body adapts remarkably well to change -- and that's the problem," Kenny said in a press release. "When the animal overstimulates its brain pleasure centers with highly palatable food, the systems adapt by decreasing their activity. However, now the animal requires constant stimulation from palatable food to avoid entering a persistent state of negative reward".
During the study, the rats lost complete control over the ability to regulate whether they were hungry, often eating despite electric shocks. When the obese rats were put on a healthy diet, they refused to eat, starving themselves for two weeks.
In another study, researchers at Albert Einstein College of Medicine in New York City showed that feeding rats a diet high in saturated fat, calories and sugar -- which is the typical make-up for a fast-food menu item -- lowered the rats ability to respond to leptin, a hormone that helps regulate eating behavior by controlling how full one feels. As rats grew fatter, the amount of leptin in their bodies increased signaling that they were dangerously close to starvation. They continued to overeat and gain weight.
Those who yo-yo diet face similar problems that those going through withdrawal do, Boston University researchers proved last year. According to Pietro Cottone, an assistant professor in the Laboratory of Addictive Disorders at BU, dieters seek out foods to avoid the negative feelings that they experience if they are deprived of their favorite comfort foods.
"These findings confirm what we and many others have suspected," Kenny said, "that over-consumption of highly pleasurable food triggers addiction-like neuroadaptive responses in brain reward circuitries, driving the development of compulsive eating. Common mechanisms may therefore underlie obesity and drug addiction."
Check out our writer's take on whether food addiction is worse than drug addiction.