As an example, he cited how activity in the anterior cingulate cortex in overweight people given food cues may be interpreted as a sign of craving. "But this is an unjustified inference because we do not know what the anterior cingulate cortex does and it far more frequently related to other processes than to craving."
Dr. Fletcher and his colleagues’ alarm over this "oversimplification of data" prompted a polite, but impassioned, back and forth with Dr. Gearhardt and her associates, published in Nature Reviews Neuroscience (2012;13:279-86 [doi:10.1038/nrn3212]); (2012;13:514 [doi:10.1038/nrn3212-c1]); (2012;13:514 [doi:10.1038/nrn3212-c2]).
In the first of these editorials, Dr. Fletcher and his coauthors wrote that "the messages now emerging from the neuroscientific research community may therefore have an unprecedented impact on policy development," and in another, urged the adoption of "a more detailed consideration" of how to explore food addiction, particularly since cognitive neuroscience is already moving the field beyond ideas based "purely on clinical overlap" and the model of addiction as delineated in the DSM-IV-TR.
Obesity subsets
"Dr. Fletcher and I agree that the concept of ‘food addiction’ is still an open question," Dr. Gearhardt said in an interview. "My group believes that there is evidence building that suggests it is plausible that an addictive process contributes to problematic eating in some circumstances, especially for eaters who exhibit behavioral phenotypes."
Binge eating, emotional eating, and other pathologies surrounding attitudes toward food also were noted in participants with high YFAS scores in Dr. Gearhardt’s study. "We see evidence of addictive-like processes contributing to problematic eating even for individuals who do not meet the criteria for BED," she said.
Dr. Fletcher noted that "there is a clear degree of clinical overlap between obesity and binge eating, particularly binge eating disorder and drug addiction." Specifically, tolerance, withdrawal, persistent desire for food, eating more than intended, and the diminishment of social engagement in exchange for more time spent acquiring and ingesting food all parallel drug addiction. "However, we don’t know what the overlap is," said Dr. Fletcher. "Is it sugar? Is it fat? Is it a combination? We really don’t know yet."
Populations vs. individuals
"If certain foods are addictive, this may partially explain the difficulty people experience in achieving sustainable weight loss," according to Dr. Gearhardt in commenting on the fMRI study results. "Ubiquitous food advertising and the availability of inexpensive palatable foods may make it extremely difficult to adhere to healthier food choices because the omnipresent food cues trigger the reward system."
Dr. Gearhardt speculated that a focus on specific food ingredients being at the root of addiction-linked obesity may spur activism by manufacturers. "The food industry will likely use any inconsistency in the food addiction literature to plant doubt, attack scientists’ credibility, or fund negative studies," they wrote.
By focusing on how detrimental the food environment has become as a result of "heavily marketed foods that interact with the brain in harmful ways," the public may be more likely to support restrictive policies such as "taxing addictive foods, limiting marketing of these foods to children, and enacting zoning laws that limit the number of vendors selling such foods" among other measures, she wrote.
Dr. Fletcher acknowledged that there is likely a legitimate "battle to be joined" against marketers of junk food and other agents contributing to a deleterious food environment, but attacking the problem at the societal level without consideration of the potential impact on the individual will ultimately backfire. "We must be very careful about how we line up our troops," he said.
"Changing behavior at a population level, which indubitably is required, is not going to be easy," said Dr. Ziauddeen. "As well as the resistance of those with vested interests, such changes will be considered widely unacceptable if they are perceived to entail a loss of liberty."
Although Dr. Fletcher and Dr. Ziauddeen agree a lack of willpower and moral frailty are antiquated notions of why people become obese, assuming that diagnosing people as food addicts will protect them, either from stigmatization or any unforeseen effects of policy changes, is short-sighted.
"Based on our experience with drug addictions over the centuries, it is hard to think that food addiction will not come with some stigma and the consequences thereof," he said.
And Dr. Ziauddeen agreed that, "If the science is shaky and hard to defend, it will be ripped apart." Beyond it possibly being "indefensible" in the face of the opposition from processed food manufacturers, thus setting the field back on its heels, there is the danger of a loss of personal liberty that results, not for the sake of the greater good, but solely from policies based on shoddy science.