Food addiction appears to be associated with the same type of reward-related neural activation that is often implicated in substance dependence, results from a small imaging study demonstrated.
"If certain foods are addictive, this may partially explain the difficulty people experience in achieving sustainable weight loss," researchers led by Ashley N. Gearhardt, of Yale University, New Haven, Conn., reported online April 4 in the Archives of General Psychiatry. "If food cues take on enhanced motivational properties in a manner analogous to drug cues, efforts to change the current food environment may be critical to successful weight loss and prevention efforts."
In what they said is the first study of its kind, Ms. Gearhardt, a clinical psychology doctoral student at Yale, and her associates examined the role of food addiction symptoms as assessed by the 25-item Yale Food Addiction Scale (YFAS) with neural activation in response to cues signaling impending delivery of a highly palatable food (chocolate milkshake) vs. a tasteless control solution, as well as intake of a chocolate milkshake vs. a tasteless solution among 48 healthy young women who ranged from lean to obese.
Study participants were enrolled in a program developed to help people achieve and maintain a healthy weight. Women who reported DSM-IV binge eating were excluded from analysis, as were smokers, women who reported using psychotropic medications or illicit drugs in the past 3 months, those who sustained a head injury with loss of consciousness within the past 3 months, and those with Axis I disorders. The mean age of the participants was 21 years, and their mean body mass index (BMI) was 28 kg/m2 (Arch. Gen. Psychiatry 2011 April 4 [doi:10.1001/archgenpsychiatry.2011.32]).
For the functional magnetic resonance imaging (fMRI) portion of the trial, stimuli consisted of two images – a glass of chocolate milkshake and a glass of water – that signaled the delivery of either 0.5 mL of milkshake or a calorie-free tasteless solution designed to mimic the taste of natural saliva. The images were presented for 2 seconds. Delivery of either substance occurred 5 seconds after the onset of cue and lasted 5 seconds.
The researchers reported results from a final sample of 39 study participants. Food addiction scores on the YFAS correlated positively with activation of the left anterior cingulate cortex (ACC), left medial orbitofrontal cortex (OFC), and left amygdala in response to anticipated intake of palatable food. All peaks remained statistically significant after adjustment for BMI.
"The ACC and medial OFC have both been implicated in motivation to feed and to consume drugs among individuals with substance dependence," the researchers noted. "Elevated ACC activation in response to alcohol-related cues is also associated with reduced D2 receptor availability and increased risk for relapse. Similarly, increased activation in the amygdala is associated with increased appetite motivation and exposure to foods with greater motivational and incentive value."
Compared with their counterparts who had low food addiction scores, those with high food addiction scores showed greater activation in the dorsolateral prefrontal cortex (DLPFC) in response to anticipated intake of palatable food, as well as less activation in the left lateral OFC. At least one previously published study, the researchers noted, "found that participants who attempted to resist pleasurable foods also exhibited elevated DLPFC activation, which was linked to reduced activity in areas implicated in coding food reward, such as the ventromedial prefrontal cortex. Thus, participants with higher food addiction scores may respond to increased appetitive motivation for food by attempting to implement self-control strategies."
Dr. Mark S. Gold said in an interview that the findings confirm observations that he and his group at the University of Florida, Gainesville, have made about hedonic or addictive eating.
"We have observed patients who quit smoking only to overeat and gain weight," said Dr. Gold, Distinguished Professor of Psychiatry & Neuroscience and chairman of the psychiatry department at the university. "We have also observed morbidly obese patients who have had successful bariatric surgery with large weight loss become alcoholics. Drugs and food compete in the brain for the same reinforcement sites," he noted.
"For food addicts, addiction treatment is more logical than current treatments that they have to choose from," he said.
Ms. Gearhardt and her associates acknowledged certain limitations of the study, including its small sample size, cross-sectional design, and the fact that only women were assessed. They recommended that future research assess the impact of neural activation in response to food advertisements as well as measure feelings of loss of control and ad libitum food consumption. "Further, the use of functional MRI technology does not allow for the direct measurement of dopamine release or dopamine receptors," they wrote. "It will be important to examine induced dopamine release and D2 receptor availability in participants who report indicators of food addiction."