Redefining Obesity Beyond Numbers

As I pointed out in yesterday’s post, there appeared to be broad acceptance for the notion that obesity is a chronic medical disease at the recent 5th Canadian Obesity Summit.

In my opening address to the delegates, however, I emphasised that acceptance of obesity as a chronic medical diagnosis requires modification of the definition of obesity to ensure that people diagnosed with this condition do in fact have significant health impairments that warrant them being considered ‘sick’.

This is where, the current commonly used ‘definition’ of obesity based on BMI breaks down, as it would ‘misdiagnose’ a significant proportion of Canadians with having a ‘disease’, when in fact they may be perfectly healthy. Moreover, the current BMI-based ‘definition’ of obesity would exclude an even larger group of individuals, who may stand to benefit from anti-obesity treatments as having a BMI that is too low.

Let us recall that BMI is really just a measure of size and not a direct measure of actual health.

As discussed in a recent editorial published in OBESITY, we have suggested that it would only take a minor (but important) modification of the current WHO definition of obesity to ensure that this label is only applied to people whose health is in fact affected by their body fat.

Thus, we have suggested that the current WHO definition,

“The presence of abnormal or excess body fat that may impair health.”  

be modified to

“The presence of abnormal or excess body fat that impairs health.” 

This simple change to the wording would have significant implications in that obesity would move from simply being a term used to describe a risk factor (“may impair health“) to being an actual disease (“impairs health“), with all of its consequences for policy, regulators, healthcare systems, research, and clinical practice.

Before anyone thinks that this would be far too cumbersome or impractical, let us remind ourselves that such diagnostic approaches are standard practice for a wide range of other diseases that require a clinical encounter, laboratory testing, and/or diagnostic imaging for their diagnosis. In fact, there are very few diseases that can be reliably diagnosed with just a single measure or test.


“…in clinical practice, assessing whether or not abnormal or excess weight is impairing someone’s health should not pose a major diagnostic dilemma. In the vast majority of patients, a few interview questions, a brief physical exam, and a short panel of routine lab tests should readily establish (or rule out) the diagnosis of obesity.”

“Of course, there will always be borderline cases in which the signs and symptoms are too vague or too subjective to be diagnostic — but that, again, is not unlike other diseases in which borderline cases may require a more intense work-up or simply a watch-and-wait approach.”

“Moreover, in some cases, it may be rather difficult to establish whether a given health impairment is indeed due to the presence of abnormal or excess body fat. In these cases, it may be prudent to use an ex juvantibus (from Latin, meaning “from that which helps”) approach to confirm or discard the diagnosis of obesity based on whether said signs or symptoms (and not just body weight) respond positively to weight loss treatments.”

Such a redefinition of obesity would likely also have implications for how we apply the Edmonton Obesity Staging System to describe the severity of this disease. Thus, there would no longer be an EOSS Stage 0, as (by definition), these individuals do not have any mental, medical, or functional impairments attributable (wholly or in part) to their body fat. Moreover, EOSS Stage 1, may need to be redefined as “pre-obesity”, thus reserving the term “obesity” only for individuals who have at least EOSS Stage 2 or greater.

As for redefining obesity, let us remind ourselves that,

“Throughout medical history, disease definitions have often been subjected to refinements and alterations, reflecting advances in our understanding of the disease process as well as in diagnostic and therapeutic approaches. A redefinition of obesity based on actual health status would help us refocus our attention on ensuring that obesity treatments reach those who stand to benefit most rather than anyone who happens to exceed a certain size.

As importantly, this redefinition of obesity would also allow individuals,whose health is clearly being impaired by the presence of abnormal body fat, to access obesity treatments regardless of their shape or size.”

Redefining obesity based on clinical assessments would not necessarily mean that we discard BMI entirely from obesity research – it will certainly remain a valid measure for population studies and perhaps even continue its existence as a screening test to identify people likely to have obesity. BMI however, would no longer be used to diagnose this medical disease.

Edmonton, AB