Redefining obesity: Beyond the numbers

Abstract

Both the American and Canadian Medical Associations have now declared obesity to be a chronic medical disease, not unlike type 2 diabetes or hypertension (1, 2). However, recognition of obesity as a disease is by no means universally accepted, no doubt reflecting the semantic problem: there is no general agreement on what constitutes a disease. This lack of a generally accepted definition prompted a seminal discussion, commissioned by The Obesity Society in 2008, with a focus on disease definitions and how they apply to obesity. The group suggested that "considering obesity a disease is likely to have far more positive than negative consequences and to benefit the greater good by soliciting more resources into prevention, treatment, and research of obesity; encouraging more high-quality caring professionals to view treating the obese patient as a vocation worthy of effort and respect; and reducing the stigma and discrimination heaped on many obese persons" (3). Thus, if we accept the benefits of labelling obesity a "disease," we need to carefully examine how this "disease" is to be diagnosed in a given individual. A good place to start would be with the World Health Organization's long-standing definition of obesity as "abnormal or excessive fat accumulation that may impair health" (4). However, to use this as a definition of an actual "disease," it would be prudent to remove the word "may." This change in wording, albeit minor, would, in fact, change the whole nature of the discussion. The defining criterion for whether a given individual has the "disease" now is not whether that person has excessive body fat or even whether that fat is "abnormal," but rather whether abnormal or excessive body fat is actually impairing that person's health. With this change in definition, we can no longer rely on anthropometric measures for diagnosis. Even the most fervent supporters of BMI will concede that not everyone above a certain BMI cutoff should automatically be considered "diseased," while not everyone below that BMI should be deemed free of health problems potentially ameliorated by weight loss. This is not to say that BMI would no longer serve as a practical screening tool to help identify people at risk for obesity—but it would no longer be considered "diagnostic" or the defining characteristic of this disease. It would, in fact, take more than a scale or a measuring tape to diagnose obesity. Using an actual measure of health to define obesity (rather than simply a measure of shape or size) solves a number of important societal and clinical problems. For one, we would no longer "misdiagnose" people who are "fat but fit" (for whom weight loss would provide little, if any, proven benefits) as having obesity. At the other end of the spectrum, without having to apply a BMI cutoff, one can readily diagnose obesity in individuals well below a BMI of 30 kg/m2, whose health is clearly being impaired by the presence of an extra pound or two of visceral fat ("thin-but-metabolically-obese"). Furthermore, we would no longer have to debate whether or not a mixed-race individual meets the BMI criteria for one race or the other or how to diagnose obesity in populations in which there are no established validated BMI cutoffs. Likewise, in clinical practice, the question to ask in any patient presenting with abnormal or excess body fat should be whether this fat is impairing health (or, conversely, whether a given health problem is directly impacted by the presence of abnormal or excess body fat). Here, given the potentially multidimensional impact of body fat, it would be prudent to apply a broad definition of health that includes physical, mental, and social well-being. Thus, an individual whose health is impaired due to the mechanical or metabolic consequences of excess weight should as much be considered as having obesity as someone who is struggling with depression, social anxiety, or is otherwise unable to engage in normal social interactions and activities due to excess body fat. Such a definition of obesity would require a full clinical assessment of each patient by a qualified health practitioner. Only a comprehensive interview together with a physical exam as well as relevant laboratory and imaging tests would establish (or rule out) the diagnosis "obesity" in a given individual. This approach would be very much in line with recent proposals for obesity classification systems like the Edmonton Obesity Staging System (5) or the King's Criteria (6), which include assessment of physical, mental, and functional health to define and characterize severity of this disease. It is also important to note that the Obesity Medical Association is now promoting the term "adiposopathy" in its algorithm (7), while the American Association of Clinical Endocrinologists / American College of Endocrinology has published Comprehensive Clinical Practice Guidelines for Medical Care of Patients with Obesity that utilizes a cardiometabolic s