- Obesity was recognized as a disease between 2013 and 2022 by several medical societies and countries.
- The conceptualization of obesity as a disease or a risk factor is still highly controversial.
- An international commission aims to identify clinical and biological criteria for diagnosing clinical obesity.
Obesity was recognized as a disease between 2013 and 2022 by several medical societies and countries.
For example, the 2020 Canadian Adult Obesity Clinical Practice Guidelines define obesity as a "complex chronic disease in which abnormal or excess body fat (adiposity) impairs health, increases the risk of long-term medical complications, and reduces lifespan.”
However, the conceptualization of obesity as a disease, and not simply a risk factor for other diseases, is still highly controversial and has important implications for both public health interventions and people living with higher weight.
Arguments Against the Definition of Obesity as a Disease
Three main arguments are made by those who are against defining obesity as a disease.
- Obesity as a disease can negatively affect people with obesity and the population's health. This conceptualization can reduce or eliminate individual responsibility and encourage adopting and maintaining an unhealthy lifestyle and harm prevention interventions to address rising obesity rates globally. (This argument has been criticized because it reflects the weight stigma in Western societies.)
- Body mass index (BMI) in the obesity range (i.e.,≥ 30 kg/m2) is associated with an increased risk of disease and death in the population (not in a single individual), and it is not a disease per se. Some are diseases associated with obesity (e.g., cardiovascular diseases, type 2 diabetes, some cancers) that develop even in the absence of obesity. In addition, many people with a BMI in the range of obesity do not have impaired organs or signs and symptoms of physical disability.
- The generic definition of obesity based only on BMI would classify 30 percent or more of the population of many nations as sick. This definition would make more than a third of these populations entitled to costly treatment with the unjustified use of drugs, medical technologies and surgical procedures, and disability claims with the consequence of making obesity a financially unsustainable and socially intractable problem.
Arguments in Favor of Defining Obesity as a Disease
A disease to be such must have a pathogenic cause that determines pathophysiological alterations (of the organs) and clinical manifestations. According to many authors, obesity meets this definition for the following reasons:
- The complex interaction of several genetic and environmental factors causes it. In particular, genetic factors seem to promote the development and maintenance of obesity, influencing food intake at the central nervous system level.
- Excess intrabdominal adipose tissue accumulation, also termed visceral obesity, is associated with harmful cardiometabolic consequences. Indeed, the progressive accumulation of visceral fat creates a situation of hypertrophy and necrosis of adipocytes, partly due to abnormalities in oxygen tension in expanded fat deposits and the recruitment of macrophages with an inflammatory phenotype (macrophages M1), which determines a state of low-grade inflammation, which in turn favors the development of hyperinsulinemia and cardiometabolic complications. Moreover, visceral fat is a hyperlipolytic tissue resistant to the antilipolytic effect of insulin that determines the influx of fatty acids to the liver that produces damage to liver metabolism with excessive production of apoprotein B containing lipoproteins, increased hepatic production of glucose, reduced hepatic degradation of insulin, resulting in hyperinsulinemia.
- Excess adipose tissue, regardless of its localization, also gradually worsens physical fitness, limits daily activities, and develops physical disability.
Defining obesity as a disease in its own right is therefore consistent with this evidence and provides greater medical legitimacy to the condition. This validity could help increase access to obesity health care for those in need and plausibly reduce the social weight stigma.
Balanced View: Obesity Can Be a Disease and a Risk Factor
According to some authors, whether obesity is a disease or a risk factor for developing future diseases is ill-conceived because it presupposes an all-or-nothing view in which obesity (i.e., excess adiposity) is always or is never a disease. Current evidence suggests that obesity can be a risk factor and, at times, a disease.
The BMI thresholds historically used to define obesity have been designed and studied as predictors of disease or future mortality but not as measures of existing disease. For this reason, the exclusive use of the threshold of a BMI ≥ 30 cannot be used to define the attribution of disease status to obesity.
A striking example of BMI limitations concerns individuals with BMI values in the normal range but present metabolic complications commonly found in people with obesity. In contrast, some individuals with a BMI ≥ 30 do not have insulin resistance or dyslipidemia.
Commission to Define Clinical Obesity
We do not yet have a definition of obesity based on distinctive clinical manifestations that reflect the presence of excess body fat or abnormal (adiposity) in itself on the normal functioning of the organs and the individual. To address this problem, a group of international experts chaired by Professor Francesco Rubino of King's College London recently established the Lancet Diabetes & Endocrinology Commission on clinical obesity.
The Commission aims to identify clinical and biological criteria for diagnosing clinical obesity. The challenge is to reach a shared definition of "clinical obesity," which indicates a condition in which the health risk associated with excess adiposity has already materialized and is objectively documented by specific signs and symptoms that reflect biological alterations of tissues and organs, consistent with existing disease and not dependent on the presence of other comorbidities.
The reformulation of obesity into non-clinical or clinical obesity has the advantage of providing a crucial tool for how we conceptualize and treat obesity by overcoming irrational beliefs that maintain the weight stigma and allowing us to identify appropriate targets that, depending on the case, may relate to prevention and public health interventions or treatment.
Rubino, F., Batterham, R. L., Koch, M., Mingrone, G., le Roux, C. W., Farooqi, I. S., . . . Cummings, D. E. (2023). Lancet Diabetes & Endocrinology Commission on the Definition and Diagnosis of Clinical Obesity. Lancet Diabetes Endocrinol, 11(4), 226-228. doi:10.1016/S2213-8587(23)00058-X
Wharton, S., Lau, D. C. W., Vallis, M., Sharma, A. M., Biertho, L., Campbell-Scherer, D., . . . Wicklum, S. (2020). Obesity in adults: a clinical practice guideline. CMAJ: Canadian Medical Association Journal, 192(31), E875-E891. doi:10.1503/cmaj.191707