Obesity as a Disease: A White Paper on Evidence and Arguments Commissioned by the Council of The Obesity Society

The Obesity Society (TOS) commissioned a panel of experts from among its members to undertake a review of the issue of labeling obesity a disease and to examine pertinent evidence and arguments. The panel unanimously and strongly stated that obesity is a complex condition with many causal contributors, including many factors that are largely beyond individuals' control; that obesity causes much suffering; that obesity causally contributes to ill health, functional impairment, reduced quality of life, serious disease, and greater mortality; that successful treatment, although difficult to achieve, produces many benefits; that obese persons are subject to enormous societal stigma and discrimination; and that obese persons deserve better. Whether obesity should be declared a disease is controversial, and thoughtful arguments have been made on both sides of the issue. The panel recognized that there is a clear majority view among the general public as well as among authoritative bodies that it is reasonable to call obesity a disease. The panel reviewed three broad classes of argument as to whether obesity is rightly classified as a disease. The first, the scientific approach, proceeds in two conceptually simple steps: i) identify the characteristics that entities must have to be considered diseases and ii) examine empirical evidence to determine whether obesity possesses those characteristics. The scientific approach would be well suited to answering the question “is obesity a disease?” rather than “should we consider obesity a disease?,” were the former question answerable. However, after much deliberation, the panel concluded that the former question is ill posed and does not admit an answer. This is not because of a lack of agreement or understanding about obesity but rather because of a lack of a clear, specific, widely accepted, and scientifically applicable definition of “disease” that allows one to objectively and empirically determine whether specific conditions are diseases. The second type of argument, the forensic approach, entailed looking to the public statements of authoritative bodies as evidence of whether obesity is a disease or should be considered a disease. A nearly exhaustive search for and consideration of the statements made by ostensibly authoritative bodies made apparent that there is a clear and strong majority leaning—although not complete consensus—toward obesity being a disease. However, although some authoritative bodies have offered statements that obesity is (or is not) a disease, very few of them have published a thorough and rigorous argument or evidential basis in support of the statement. Moreover, and far more importantly, the panel held that the opinions of authoritative bodies tell us—at most—what is lawful, consistent with mainstream opinions, or likely to be supported by others. Such opinions are insufficient to tell us what is true or what is right. The panel strongly endorsed the position that there can be no higher authority than reason. Hence, the forensic approach was judged to be inadequate to help us determine either whether obesity is a disease or whether it should be considered a disease. The third approach to this question we termed the utilitarian approach. Recognizing that there is no clear agreed-on definition of disease with precise, assessable criteria that can be articulated, it seems that conditions that produce adverse health outcomes come to be considered diseases as the result of a social process when it is assessed to be beneficial to the greater good that they be so judged. Such judgments about likely benefit to the greater good are utilitarian judgments that may take empirical input but must also assume certain values. We considered the likely outcomes of considering obesity to be a disease to address the question “should obesity be declared a disease?” (as opposed to “is obesity a disease?”). Necessarily, our utilitarian analysis was speculative. The disease label tends to confer certain benefits, obligations, motivations, and legal considerations in our society. The panel concluded 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. The panel felt that this utilitarian analysis was a legitimate approach to addressing the topic, as well as the approach used for many other conditions labeled diseases, even if not explicitly so. Thus, although one cannot scientifically prove either that obesity is a disease or that it is not a disease, a utilitarian approach supports the position that obesity should be declared a disease. The prevalence of obesity has been increasing for over a century (1) and has increased substantially in the past several decades (2). Clear and consistent evidence shows that obesity increases the risk of many morbidities and reduces both the quality and the quantity of life (3,4,5). These facts lead many to conclude that the time for concerted action to reduce levels of obesity and the deleterious effects of obesity is clearly upon us. In preparing for such action and in an attempt to enlist the participation and aid of broad sectors of society, many believe that labeling obesity a disease and having society accept this label is vital. However, is the label warranted? Prominent obesity experts have offered the opinion that it is indeed warranted, but equally prominent (although fewer) obesity experts have disagreed. Similarly, writers in the mass media, advocates for obese persons' rights and welfare, and members of the general public have also expressed strong opinions both for and against the appropriateness of labeling obesity a disease. The National Consumers Union reported that in a national survey 78% of respondents somewhat or strongly agreed with the statement “obesity is a serious chronic disease” and 22% did not (6). Given this diversity of views, TOS commissioned a panel of experts from among its members to undertake a rigorous review of the issue of labeling obesity a disease and of the pertinent evidence and arguments. This report presents the results of that review. The formal question to be addressed is “should obesity be considered a disease?.” This question is closely related to but fundamentally distinct from the question “is obesity a disease?.” The panel concluded that the latter question—a seemingly empirical question that should (in principle) yield to scientific inquiry—is ill posed in that its sensibility is based on premises that are not true. It is therefore insensible and unanswerable. In contrast, “should obesity be considered a disease?” is a question that is fundamentally not empirical or scientific. Its reliance on the word “should” (read equally “ought”) immediately signals that it is a social, political, and fundamentally ethical and moral question (7), because what one should do depends not only on the likely effects of one's actions (empirical input) but fundamentally on how one values various outcomes. Such values, although scientifically estimable, are not scientifically determinable. That is, although ethical and moral questions may be addressed in part by using scientifically generated empirical input (8), such questions should not be conflated with scientifically evaluable empirical questions that concern matters of fact rather than matters of value. Finally, there is substantial interest in many contexts as to whether obesity constitutes a disability (e.g., refs. 9, 10); to avoid any confusion, we note that this should be recognized as a distinct question that we are not addressing here. As others have remarked (e.g., ref. 11) and as we elaborate below, whether obesity is considered a disease may have a profound impact on the lives of millions of obese individuals as well as on multiple aspects of our society. We therefore believe that, as the leading professional obesity society in North America, TOS has the obligation to provide leadership on this issue. We hope that by providing an answer to the question of whether obesity should be considered a disease—an answer that is based on sound reasoning and represents the collective wisdom of this leading professional society—we may catalyze society at large to come to a consensus view on this point. In turn, we hope that reaching such a consensus may enable efforts to ameliorate the problems of obesity to move forward more effectively. Our panel struggled with the complexity of the issues surrounding the question; the members held a diversity of views, as did the field of obesity researchers. Nevertheless, the panel's members wish to note that there was absolutely no disagreement on the following fundamental points, which we voice loudly and clearly: •Obesity is a complex condition with many causal contributors, including genetic ones and many environmental factors that are largely beyond individuals' abilities to choose or control (12,13,14,15). •Obesity causes much suffering. •Obesity causally leads to many aspects of ill health (16), to functional impairment (17) and reduced quality of life (18), to serious disease (4), and to greater mortality (19). Successful treatment, although difficult to achieve, produces many benefits, including prevention of disease (20) and reduced mortality rate (21,22,23). •Obese persons are subject to severe societal discrimination in ways that those with seemingly similar chronic conditions, such as hypertension, dyslipidemia, and diabetes, are not. For example, obese individuals are waited on more slowly by salespersons, less likely to be rented apartments, less likely to be offered jobs, even when as qualified as other applicants, and less likely to receive support for higher education from parents, and often are looked down on by educators and health professionals (24,25,26). These points underpin our concern for obese individuals and provide the motivation for undertaking the charge of this panel. The Executive Committee of TOS wished to have a formal position statement on whether obesity is justifiably called and should be declared a disease and commissioned this white paper as a critical evaluation of relevant arguments and evidence. The panel, convened from among TOS's leaders and members, equally represented those who had previously expressed skepticism and those who had expressed belief that obesity is justifiably called a disease. The panel attempted to conduct an exhaustive search of the professional literature on this topic, discussed the various arguments that had been advanced, and agreed that the highest standards of intellectual rigor should be applied when considering the cogency of any position. Differences of opinion were discussed until consensus was reached in most cases. Some topics resisted consensus, and the panel members' divergent viewpoints are reflected in this document. The final draft was presented to TOS's council to be used as a basis of informed decision making about whether to offer a formal position statement on obesity as a disease and, if so, what that position should be. We define obesity as an excess of body fat. It may be of either total body fat or a particular depot of body fat. The excess may even be in the morphology and function of body fat such that, for example, adipocytes, independent of total fat mass or fat mass distribution, are excessively enlarged. The adverse health consequences of accumulation of enlarged visceral or other adipocytes may tentatively be accounted for by enhanced secretion of most products of adipocytes that act as endocrine and paracrine factors on other cells, as well as the reduced production of adiponectin (27). Note that we do not define obesity as a BMI greater than or equal to 30 kg/m2. That is a useful operational definition (28) for many contexts but should not be used as the conceptual definition. Even as an operational definition, a BMI greater than 30 may not be ideal, and authors are beginning to question whether the field should adopt a more useful operational definition (e.g., refs. 29, 30). In our definition of obesity, excess of body fat denotes an amount sufficiently large to cause reduced health or longevity. This reduction in health will not be noticeable in all cases and may not be realized immediately, but obesity probabilistically threatens to reduce health in the future even if no health impairment is observed in an individual in the present. For example, as fat cells increase in size, they begin to produce substances (e.g., tumor necrosis factor-α) in excess of normal levels. For some people this causes insulin resistance and diabetes, but for others who have sufficient adaptive capacity, no deterioration of body function or health is apparent. As with hypertension and elevated blood glucose, many people initially demonstrate no obvious health problem yet health deteriorates over time. The effects of accumulation of adipose tissue depots and possibly of enlarged adipocytes appear to vary as a function of age, ethnicity, sex, and other factors. Hence, operational definitions of obesity may also need to vary as a function of these factors even if the conceptual definition remains constant. To address the question of whether obesity should be considered a disease, we identified three major approaches that have been or could be used, approaches that go beyond rhetorical assertions. We term these the “scientific approach,” the “forensic approach,” and the “utilitarian approach.” (Commonly used arguments that we believe to be patently invalid and worthy of only brief consideration are listed in Appendix 1.) The authors of most documents that attempt to address the issue of obesity as a disease have not described a thorough and organized argument or approach to reaching their conclusions. This does not necessarily mean that they did not use such an argument or approach, only that none was described. Authors who have tried to be more thorough and rigorous in their analysis have generally used the scientific approach, the forensic approach, or both. In this document we argue that the scientific and forensic approaches are not useful in addressing this question and then move to the utilitarian approach, which, to our knowledge, has not been used as a primary approach. We argue that this is the most appropriate approach and use it to form the basis of our conclusion. More than 2,500 years ago the physician Hippocrates, often called the father of medicine, recognized that people who were overweight were at higher risk for sudden death. Closer to our times, Malcolm Flemyng, a physician from the 18th century who wrote one of the two earliest books on overweight in the English language, stated that “corpulency” (i.e., obesity) can be a disease in some cases. Table 1 lists historical quotations on obesity as a disease, from the 1600s to 1934. Inspection of these quotations makes clear that the idea that obesity may appropriately be called a disease is not new; it has recurred throughout the past several hundred years. Multiple authors (see, for example, refs. 31,32,33) said that obesity is appropriately considered a disease only when it reaches a certain degree of severity, implying that they conceived of obesity as a disease in some but clearly not all cases. Conversely, some authors (e.g., refs. 36,37) said that obesity is not a disease in all cases, implying that it is in some. None of these authors provided a through discussion of why obesity should or should not be considered a disease. The primary form of “argument” used was simply ipse dixit, a rhetorical assertion without a valid supporting argument. This has been the most commonly used approach to this issue, even in the past 20 years, and remains the one in most frequent use. The scientific approach is well suited to the question “is obesity a disease?” or, more abstractly and generically, to the question “does a class of entities A rightly belong as a subset of the larger class of entities denoted B?” Phrased in this more generic way, the way to proceed is obvious. It involves two conceptually simple steps. Step 1 is to identify the characteristics that entities must have to be considered members of class B. Step 2 is to examine empirical evidence to determine whether all entities in class A possess those characteristics. This is an approach taken by several authors (e.g., refs. 39,40,41,42), at least one legal proceeding (43), and a recent video, “Is Obesity a Disease?,” produced by the American Medical Association (AMA) (44) and offered on the website of the US Agency for Healthcare Research and Quality (45). Some key facts are germane in attempting to scientifically address the issue of obesity as a disease. In most cases, these facts are well known and well established and we do not dwell on the evidential basis. Instead, we simply state the fact and refer to an appropriate source for details of supporting evidence. 1. Obesity (or, more precisely, variations in BMI or body fat mass among individuals) has many causes both across and within individuals (12,13,14). 2. The prevalence of obesity has increased substantially in the past half century, both within the United States and globally. This increase has occurred in virtually every age, race, and sex group (46). A current estimate is that roughly one-third of US adults (more than 50 million persons) are obese (46). 3. Obesity increases the risk of many morbidities (5,41,47) and reduces quality of life (18), functional capacity (17), and lifespan (19). 4. Animal model studies (48,49,50), studies of lifestyle intervention in humans (20), and studies of bariatric surgery in humans (21,22,23) all show that when weight and fat loss can be induced by medically recommended interventions among obese organisms, morbidities are reduced and lifespan can be increased.* 5. Statement 3 applies in probability; that is, any obese individual may experience only minor adverse effects of obesity in any one or more of these categories and may experience no adverse effects of obesity in some categories (39,41,51). 6. Apart from an expanded fat mass, which is inherent in the definition of obesity used herein and in a prior TOS (formerly NAASO) position statement (52), there is no characteristic sign or symptom that is present in all obese persons (39). 7. Obesity, at least when operationally defined as the exceeding of a specific amount of body fat or a specific BMI, is also associated with certain health benefits (53). These include the now rarely needed but obvious protection against starvation in times of food scarcity (54), protection against osteoporosis and fractures in the elderly (51), possible prevention of frailty in the elderly, reduced mortality rate in the elderly with mild obesity (55), and reduced mortality rate in certain severe illnesses or injuries (56). The extent to which these associations represent causation is not clear in all cases. Kincaid (57) wrote, is a and about how to define disease and whether such definitions are two at of health are the The that disease is from disease is from the In the function disease when an is not the that it to a somewhat approach, and multiple and and points to most definitions of a condition of the its or or an from or other having a group of or from normal or function described as or impairment of normal of or a similar approach, the American Medical Association (44) offered the three points in 1 and that all three conditions need to be to for obesity to be defined as a disease. A from the American Medical “Is Obesity a The US and a definition of disease based on an thoughtful of the and the had to a definition of disease. The of would not be to statements that a could be used to or a disease but could about the effects on the or function of the The which in public and a public that and of a broad of and the of the the to a definition in as part of the of the and which disease as to an or of the body such that it does not function (e.g., or a state of health leading to such (e.g., that diseases from (e.g., are not in this As in Appendix the concluded that obesity is a disease by this definition and and on a definition of disease in Medical that described as a or of body or 2. A by at least two of these recognized group of and or consistent 3. the of when is with a of the definitions to apparent some of the with this approach. the definitions definition should be considered the definitions and they on their likely to admit to the class of diseases all the entities that and societal consensus accept as diseases, and likely to from the class of diseases all the entities that and societal consensus would not accept as to what Kincaid (57) the it would be difficult to argue that obesity constitutes a that roughly one-third of the US is Moreover, even if we that one-third was a sufficient for obesity to the disease such a decision process would that if obesity occurred in more than of the as some authors have it will (e.g., ref. The decision to a condition as a disease simply because many people have it makes In the function approaches described by Kincaid when an is not the that it to However, not all would accept such a definition. For example, a document by the National of said that disease is not a a functional that the or to the an that is not is not sufficient for the condition to be labeled a disease. this and wrote, the of body because of an increased which the of to but one The of excess body fat is apparent in the state a reduction of fat and some as well as an increase in and and adipose tissue have been These of risk factors which can the accumulation of body fat to body on other such conditions, obesity is by the as a rather than a In contrast, others argue that, although be in some cases, this does not necessarily support the that obesity is therefore or beneficial fat against or offer some beneficial effects yet have deleterious effects that the Similarly, if there are that fat as a against environmental then those be as for are not good or in that are not closely with those in which the A of argument that the key in obesity is adipose tissue and a of adipose tissue is to excess as for future use. adipose beyond some and adipocytes cannot be adipose tissue may no this function and may result this may be it is not likely that that this is the or primary by which obesity health, and longevity. Finally, although is one function of adipose it is not the only Thus, the approach an of and does not offer a clear by which obesity may be classified as a disease. also considered these and definitions and to the that we We now consider the approach of the known facts about obesity to the definitions offered by and and and the to their key in definitions of disease, and wrote that there should be disagreement that obesity the two an excess accumulation of fat can be of as a condition of the body and the of causes is so that the causes of obesity must be However, they expressed about the third as we offered when key facts about obesity, no the condition of obesity other than excess which is the definition of Similarly, the (44) that obesity to what it listed as the second of a characteristic and the criteria must be The second of disease, characteristics or is not by are no specific of obesity and the only sign is a greater weight and an excessively large The explicitly that obesity is not a disease. Given that the that three criteria must be explicitly that one of the three is not and strongly questions the the from its of view is obvious. In contrast, to second definition of a group of and clearly all 3 not 2. The and of obesity include an excess accumulation of adipose tissue and are likely to include insulin increased glucose, elevated and levels of and and in the of the and are other the definitions used by and and the and that used by that two of three criteria be and and the all criteria to be an increase in the of and to be the of the many definitions they The for the are to but we may that they are only as by the of their does the definition used by and refer to mortality or definition does so more also on definition but to the from that of and and wrote, Medical

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