With two-thirds of American adults classified as overweight or obese, the obesity epidemic is high in the consciousness of both the public and the medical community. One area of obesity research receiving a great deal of attention lately is the considerable neurobiological overlap between addiction and some forms of obesity. Now, a review of the research has revealed strong evidence indicating that some obese individuals display pathological responses similar to those seen in addicted brains.
In an extensive new analysis, scientists led by Dr. Isabel Garcia-Garcia, a postdoctoral researcher at the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany, compared neurological responses to reward stimuli in participants with obesity, substance addiction, and non-substance (or behavioral) addiction, such as gambling.
The research, published in the journal Obesity Reviews, provides the first objective integration of fMRI (functional magnetic resonance imaging) results on studies in these areas, adding to our evolving understanding of the complex causes of obesity.
For many years, overeating and obesity were viewed as failures of willpower; doctors and nutritionists advised overweight people to simply eat less and exercise more to shed excess pounds. But new research suggests it may not be that simple.
Scientists are finding that repeated exposures to high-fat, high-sugar foods can trigger lasting brain changes that might make it difficult to resist overeating. Furthermore, those changes resemble what happens in the brain when someone is addicted to drugs, such as nicotine, alcohol, and cocaine.
In this latest study, an international group of researchers conducted a meta-analysis on 87 previous studies assessing neurological responses to reward stimuli, such as food or drug-related images. In their analysis, they compared these responses among the three groups of participants (i.e., those with obesity, substance addiction and non-substance addiction) and a control group, seeking to identify commonalities and differences in the way participants’ brains responded to the reward stimuli.
The results showed that those with substance addictions and obesity both had increased activity in the right amygdala — the part of the brain responsible for emotional processing, fear, and anxiety — in response to stimuli. They also displayed heightened activity in the brain region known as the left accumbens, which is associated with the rewarding effects of drugs of abuse, food, and sexual behavior.
The authors point out that although the neurological similarities between substance addiction and obesity are comparatively small, they are nonetheless significant because they are located in areas of the brain crucial for the processing of reward and salience (or how much an item stands out).
One explanation for the similarities is that the enhanced focus on rewarding stimuli may be associated with the presence of some compulsive-like behavior or with some degree of difficulties in impulse control, the authors suggest. Like addictive drugs, eating certain foods, particularly those high in fat, sugar, and/or salt, creates a feedback loop in the brain’s reward centers — the more you consume, the more you crave, and the harder it is for you to satisfy that craving.
Despite these similarities, food and drugs act on the brain in distinctive ways that are not entirely comparable. Whether or not the reward processes involved in obesity ‘qualify’ for the diagnosis of an addictive disorder remains an issue of ongoing debate among scientists.
Another question is, if those reward processes do meet the criteria for addictive disorders, what type of addiction is it? Some scientists say that food itself can be addictive, while others argue that it’s the act of eating — not the properties of the food — that stimulates the brain’s reward pathway and, in some cases, leads to addiction. While the evidence clearly shows that drugs of abuse can trigger physiological addiction, there is no consensus on whether food can do the same.
The authors of the review offer their perspective, suggesting that overeating is unique in the area of addictions, encompassing characteristics of both substance dependence and behavioral addictions. Highly palatable food — high in salt, fat, and/or sugar — is a dopamine-activating substance that triggers reward processes similar to those induced by drugs, and therefore introduces the possibility of physiological substance dependence. Eating, on the other hand, is similar to the behaviors that characterize non-substance addictions, such as compulsive gambling or shopping.
While debate remains, the researchers say they hope the paper’s findings will help inform treatment of obese patients and help them to achieve more efficient impulse control behavior. “Therapeutic approaches should attempt to reduce the salient and reinforcing properties of food and addiction-related stimuli and apply cognitive control strategies that can lead to a more efficient impulse control behavior,” they write.