The third item on the disease definition modification checklist developed by the Guidelines International Network (G-I-N) Preventing Overdiagnosis Working Group published in JAMA Internal Medicine, pertains to the issue of why modify the disease definition at all?
With obesity being increasingly recognize as a chronic disease, it should be evident to anyone, that the current BMI-based definition of obesity, although simple (or rather simplistic), would label a substantial number of individuals as “diseased”, who may be in rather good health and, therefore, very unlikely to benefit from any obesity treatments (overdiagnosis).
On the other hand, the current BMI-based definition excludes a vast number of people, who may very well have health impairments attributable to abnormal or excess body fat, and may thus benefit from obesity treatments (underdiagnosis).
Although there have been many suggestions for replacing BMI with other anthropometric measures (e.g. waist-to-hip ratio, ponderal index, abdominal sagittal diameter, etc.), none of these measures would guarantee that the individuals identified by such measures, would indeed have health impairments attributable to abnormal or excess weight – their sensitivity and specificity, although perhaps marginally better than BMI in identifying individuals with excess body fat, would still not pass the sniff-test for a reliable diagnostic test of an actual disease.
In fact, given the diversity and heterogeneous nature of adipose tissue, even more precise measures of actual body composition (including sophisticated imaging techniques) would still not be enough to determine whether or not body fat in a given is in fact impairing health and warrants obesity treatment.
In contrast, a definition of obesity that requires the actual demonstration of health impairments (likely) attributable to abnormal or excess body fat, via a clinical assessment, would ensure that obesity is only diagnosed in individuals, who actually have a health problem and would therefore likely benefit from obesity treatments. This may well include individuals below the current BMI cut-off.
Thus, continuing to use BMI (or any other anthropometric measure or more sophisticated estimate of body fat) is simply not an option if we are serious about calling obesity a disease.
The second item on the disease definition modification checklist developed by the Guidelines International Network (G-I-N) Preventing Overdiagnosis Working Group published in JAMA Internal Medicine, pertains to the issue of how a proposed new definition would alter the prevalence of the disease.
As indicated in the name of the working group that came up with this checklist, their primary concern is over-diagnosis or “diagnosis-creep”, as often disease modifications tend to increase the number of people covered under said new diagnosis.
So what is the implication for prevalence of obesity if we move from a definition based on BMI to one based on an actual impairment of health?
Fortunately, we have some data on this, including our own studies on the Edmonton Obesity Staging System, which ranks individuals based on the presence of obesity related impairments in mental, physical, and/or functional health.
Based on varying estimates, anywhere between 5-15% of individuals with a BMI over 30 would be considered to be rather healthy with no or minimal health risks. These people would need to be excluded, if obesity was defined as the presence of abnormal or excess body fat that impairs health (they may at best be considered to have “pre-obesity”). This would slightly reduce the number of people considered to have obesity (especially in the BMI 30-35 range).
On the other hand, an estimated 40-50% of individuals in the BMI 25-30 range, would actually have significant health problems at least in part attributable to their excess weight, and these individuals may potentially benefit from obesity treatments. Thus, such a change in definition would very substantially increase the number of individuals considered to have obesity.
This, of course is something that needs to be carefully considered, as it would clearly have implications for obesity treatment in a significant number of individuals, who at this time would not meet the criteria for obesity management.
Let us, however, remember that one would still need to demonstrate significant benefit of treatment in these newly classified individuals. before expanding the indication of existing obesity treatments to these individuals.
The first item on the disease definition modification checklist developed by the Guidelines International Network (G-I-N) Preventing Overdiagnosis Working Group published in JAMA Internal Medicine, pertains to the issue of how a proposed new definition would differ from the existing definition.
As authors are well aware, the current definition that is widely used to define obesity is based on BMI, a simple anthropometric measure calculated from body height and weight – a great measure of size, not such a great measure of health.
In contrast, the proposed definition of obesity, where obesity is defined as the presence of abnormal or excess fat that impairs health, would require the actual assessment and demonstration of the presence of health impairments attributable to a given subject’s body fat.
Thus, while anyone can currently “diagnose” obesity simply by entering height and weight into a BMI calculator and looking up the value on a BMI chart, the new definition would in fact require a full clinical assessment of an individual’s health. Such an assessment would need to look at both mental and physical health as well as overall well-being for issues that may be directly caused (or aggravated by) the presence of abnormal of excess body fat.
This does in fact bring up the issue of how exactly you would define “abnormal” or “excess” body fat and, even more importantly, how you would establish a relationship between body fat and any health impairments in a given individual.
While these issues would clearly need to be worked out, the face value of this approach should be evident in that it focusses on the issue of actual health impairments rather than an arbitrary BMI cut-off, above which everyone would be considered as having obesity.
This of course raises a number of issues around definition precision and accuracy, which is another item on the checklist and will be discussed in a future post.
However, there was also much agreement that the current criteria for diagnosing this disease, based on BMI criteria alone, has important limitations in that it may over-diagnose a significant number of individuals at no or very little imminent risk from their body fat and (even more importantly) under-diagnose a substantial number of individuals, who may well stand to benefit from anti-obesity treatments.
Thus, as my readers are well aware, I have long called for a redefinition of obesity based on the actual presence of health impairments attributable to abnormal or excess body fat.
It is thus timely that JAMA Internal Medicine has just published a seminal article by Jenny Doust and colleagues on behalf of the Guidelines International Network (G-I-N) Preventing Overdiagnosis Working Group, that provides a framework for anyone proposing changes to disease definitions.
Using a 5-step process that included (1) a literature review of issues, (2) a draft outline document, (3) a Delphi process of feedback on the list of issues, (4) a 1-day face-to-face meeting, and (5) further refinement, the group developed an 8-item checklist of items to consider when changing disease definitions.
The checklist specifically deals with the issues of definition changes, number of people affected, trigger, prognostic ability, disease definition precision and accuracy, potential benefits, potential harms, and the balance between potential harms and benefits.
The authors propose that,
“…the checklist be piloted and validated by groups developing new guidelines. We anticipate that the use of the checklist will be a first step to guidance and better documentation of definition changes prior to introducing modified disease definitions.”
No doubt it would be prudent to consider all of the identified aspects in the checklist, when considering changing the definition of obesity from one based simply on BMI to a more clinical definition, based on actual impairments in health.
In coming posts, I will consider each of the proposed checklist items and how they may apply to such a change in the definition of obesity.
Hat tip to Dr. Marcela Flores for drawing my attention to this paper
Following in the footsteps of other organisations like the American and Canadian Medical Associations, the Obesity Society, the Obesity Medical Association, and the Canadian Obesity Network, this month, the World Obesity Federation put out an official position statement on recognising obesity as a chronic relapsing progressive disease.
The position statement, published in Obesity Reviews, outlines the rationale for recognising obesity as a chronic disease and is very much in line with the thinking of the other organisations that have long supported this notion.
In an accompanying commentary, Tim Lobstein, the Director of Policy at the World Obesity Federation notes, that recognising obesity as a disease can have the following important benefits for people living with this disease:
1) A medical diagnosis can act to help people to cope with their weight concerns by reducing their internalized stigma or the belief that their problems are self-inflicted and shameful.
2) A classification of obesity as a disease, or disease process, may help to change both the public and professional discourse about blame for the condition, the latter hopefully encouraging greater empathy with patients and raising the patient’s expectations of unbiased care.
3) Recognition of obesity as a disease may have benefits in countries where health service costs are funded from insurance schemes that limit payments for non-disease conditions or risk factors.
While all of this is great, and I am truly delighted to see the World Obesity Federation come around to this statement, I do feel that the policy statement seems rather tightly locked into the notion that obesity (or at least most of it) is a disease “caused” primarily by eating too much, with the blame placed squarely on the “toxic obesogenic environment”.
Personally, I would rather see obesity as a far more etiologically heterogenous condition, where a wide range of mental, biological and societal factors (e.g. genetics, epigenetics, stress, trauma, lack of sleep, chronic pain, medications, to name a few) can promote weight gain in a given individual.
Although these factors may well operate through an overall increase in caloric consumption (or rather, a net increase in energy balance), they, and not the act of overeating per se must be seen as the underlying “root causes” of obesity.
Thus, I tend to see “overeating” (even if promoted by an obesogenic food environment) as a symptom of the underlying drivers rather than the “root cause”.
Thus, saying that obesity is primarily caused by “overeating” is perhaps similar to saying that depression is primarily caused by “unhappiness”. Readers would probably agree that such a statement regarding the etiology of depression would make little sense, as “unhappiness” is perhaps a symptom but hardly the “cause” of depression, which can be promoted by a wide range of biological, environmental and societal factors, all resulting in the underlying biology that results in the mood disorder.
Similarly, I would say that there are indeed a number of complex socio-psycho-biological factors that underly the biology that ultimately results in overeating and excess weight gain (the food environment clearly being one of these factors).
While this may seem like semantics, I do think that a more differentiated look at the underlying etiology of obesity at the individual level (rather than simply blaming it all on “overeating”), is essential for promoting a more sophisticated view of this complex chronic disease both at the level of the individual and the population.