Table of the Mortal Sins, Hieronymus Bosch

I suspect there are only a select few readers who have never gone on a diet with the intention of dropping a few pounds. Indeed, being overweight is a state with which all too many of us are familiar, with recent data indicating that over two-thirds of the U.S. population is overweight and a third is obese.1

In medicine, “obesity” and “overweight” are defined quite simply, based on a mathematical calculation called the Body Mass Index (BMI) that takes into account one’s height and weight. Online BMI calculators abound, allowing us all to quickly check where we lie on a continuum of obesity. A BMI between 20 and <25 is considered normal, a BMI between 25 and <30 is considered overweight, and a BMI > 30 is considered obese. While BMI might not be the best measure of health risk, research has consistently found that obesity is associated with greater mortality and a greater risk of high blood pressure, heart disease, diabetes, stroke, and a variety of other medical conditions.2 The risks of being overweight are less clear, though overweight is often a pathway to more concerning obesity.

But what is obesity? Is it itself a medical disease? 

That very question was debated by the American Medical Association’s (AMA) Council on Science and Public Health in 2013.3 Recognizing the lack of any clear definition of “disease,” the Council’s report instead focused on weighing the pros and cons of using that term for obesity. Arguments ran both ways. Doing so might give the problem of obesity greater recognition, leading to more funding for public health programs and more reimbursement by insurance companies for treatment. Or perhaps calling obesity a disease would have the opposite effect, leading to greater emphasis on pharmacologic and surgical treatments at the expense of public health and so-called “social solutions.” On the issue of stigma, a disease model could temper stereotypes about laziness and lack of self-control, resulting in greater acceptance of a complex etiology of obesity. Or again, the opposite might occur, with stigma increasing if we were to label the majority of the U.S. population as diseased. With no clear resolution, the Council’s report ended up without a firm recommendation, opting instead to call obesity a “major public health problem.” But soon thereafter, the AMA’s House of Delegates forged ahead anyway, overwhelmingly voting to officially declare obesity a medical disease.4

Let’s take this one step further now, posing the question of whether obesity might be best categorized not only as a medical disease, but as a psychiatric disorder. As a kind of thought experiment, I’m going to argue that indeed it would. 

Although debates about how to define a mental disorder have been ongoing for years, the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) has recently given an updated, if still imperfect, definition of mental disorder as “a syndrome characterized by clinically significant disturbance in an individual’s cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning.” Put more simply, psychiatry’s domain includes aberrant mental states and behaviors that are associated with impaired functioning.

While the underlying cause of obesity is poorly understood, the mechanics are clear – being overweight involves consuming more calories than are needed to maintain an ideal body weight.  In that sense, being overweight might best be characterized as a behavioral disorder, one in which the dysfunctional behavior in question is eating. Psychiatry already addresses other eating disorders including anorexia, bulimia, and binge-eating disorder such that extending the spectrum to obesity requires no great leap of logic.

Highlighting the behavioral core of obesity is not be equated with saying that freely-willed choices about eating are the root-cause of obesity. On the contrary, it would be more correct to say that obesity, just like any other psychiatric disorder, represents a dysfunction involving genetics, anatomy, physiology, and environmental factors that results in an inability of the brain to properly regulate behavior. In the case of obesity, the brain must ultimately decide whether to eat based on hunger, satiety and other factors, but that decision is an action influenced by things going on in other places in the body.  

For example, in recent years, obesity research has highlighted how the bacteria living inside our intestinal tracts — our “gut microbiome” — can influence nutrient metabolism and energy extraction from food.5 Based on individual differences in the gut microbiome, it appears that two people eating the same amount of food can differ in the amount of calories harvested from that food, such that one might be more likely to become obese. In that way, bacteria might be a root-cause of obesity rather than overeating per se. Likewise, several investigators have recently challenged the traditional notion that obesity is purely a disorder of overeating, noting that dietary make-up rather than caloric content might be a key determinant of fat accumulation and that adiposity itself can lead to overeating rather than only the other way around.6,7   

The take-home message here is that categorizing obesity as a psychiatric disorder has nothing to do with pointing a finger of blame at people’s behavior, just as we don’t we don’t blame depression on sloth. Human behavior has a multitude of determinants beyond conscious and free-willed choices. For the most part, modern psychiatric diagnoses have deliberately remained neutral about the etiology of mental illnesses and it is for this reason that the term “disorder” has been used in place of “disease” within the DSM. In fact, it’s something of a running joke that once the cause of a psychiatric disorder is discovered — as with say, Alzheimer’s disease — it becomes a neurological disorder. 

Still, we now have compelling animal models for addiction, with reasonably clear outlines of the neural pathways in the brain that govern behaviors associated with reward and loss of control. This has helped to build a strong case for modeling addiction as a psychiatric disorder, a viewpoint that is now widely embraced by the medical community, if still debated in other circles including the legal system. Just so, best practice addiction therapy now involves the combination of psychotherapy as well as pharmacotherapy, with several medications now approved by the Food and Drug Administration (FDA) for the treatment of alcohol dependence. 

Many researchers have applied an addiction model to at least some forms of obesity, noting similarities in terms of the immediate psychological rewards one derives from eating, a loss of behavioral control, and overlapping neural systems underlying “appetitive and consummatory behaviors.”8 Again then, adopting a psychiatric model for obesity hardly seems a stretch.

If we can accept obesity as a psychiatric disorder based on its core behavioral features and its similarities to other eating and addictive disorders, let’s now follow the AMA’s lead in discussing the pros and cons of such reclassification. What would be the point of calling obesity a psychiatric disorder?  

For one thing, as perhaps the ultimate mind-body disorder, it could be argued that obesity could really benefit from the attention of psychiatrists, who seek to understand behavior from both psychological and medical perspectives and routinely combine behavioral interventions (e.g. psychotherapy, dieting, exercise) with somatic therapies (e.g. weight loss medications, referrals for potential bariatic surgery). 

In terms of a con argument, the major issue, as always, is stigma. Unfortunately, psychiatric disorders, and addictive disorders in particular, carry substantial stigma such that while we all acknowledge being medically ill at various points in our lives, we’re often loathe to admit that we might be mentally ill. And despite the fact that overweight has become the new normal in the U.S., being "fat” is itself widely reviled and stigmatized within our “fat shaming” culture. So reclassifying obesity as a psychiatric disorder might very well compound those stigmas. 

But maybe it doesn’t have to be that way. An online survey administered to people in the U.S. and Australia found that the majority of respondents (54%) thought that obesity should be considered a form of addiction and 64% were prepared to classify it as an eating disorder.9 As with addiction, it appears that a psychiatric model of obesity has the potential to decrease stigma by undermining the myth that people are obese because they lack willpower and choose to be overweight. Participants in the survey also rated psychotherapy or counseling as the most effective treatment option for obesity by far, beating out both diet and exercise. These results provide both a rationale and hypothetical benefit to classifying obesity as a psychiatric disorder. By extension, they also suggest that the majority of the U.S. population could benefit from psychiatric care.

While many may find that last sentence especially hard to swallow, such reluctance is most likely rooted in stigma about what it means to have a psychiatric disorder and dystopian concerns about psychiatrists medicating the populace. But on the contrary, the universality of less than ideal mental health should reduce stigma and calling obesity a psychiatric disorder carries no automatic implication about medication.

Then again, if a safe and effective weight loss drug were approved by the FDA, it would almost surely jump to the top of the most-prescribed medications in short order, driven not by doctors and psychiatrists, but by consumer demand.


1. Ogden CL, Carroll MD, Kit BK et al. Prevalance of childhood and adult obesity in the United States, 2011-2102.  JAMA 2014:311:806-814.

2. Flegal KM, Kit BK, Orpana H et al. Association of all-cause mortality with overweight and obesity using standard body mass index categories: A systematic review and meta-analysis. JAMA 2013:309:71-82.



5. Kallus SJ, Brandt LJ. The intestinal microbiota and obesity. J Clin Gastroenterol 2012; 46:16-24.

6. Taubes G. The science of obesity: what do we really know about what makes us fat? An essay by Gary Taubes. BMJ 2013:346:f1050

7. Ludwig DS. Increasing adiposity: Consequence of cause of overeating? JAMA 2014:311:2167-2168.  See also:

8. Smith DG, Robbins TW.  The neurobiological underpinnings of obesity and binge eating: A rationale for adopting the food addiction model. Biol Psychiatry 2013; 73:804-810.

9. Lee NM, Lucke J, Hall D et al.  Public views on food addiction and obesity: Implications for policy and treatment. PLOS One 2013; e74836.

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