Defining Obesity, Fooled by Appearances

Escaping CriticismDefining obesity is a tricky enterprise for the simple reason that we are all easily fooled by appearances. But obesity is not a disease of size or appearance. It’s a disease of dysregulated adipose tissue.

This fact doesn’t stop people from thinking – falsely – that they can size up a person’s metabolic health based on appearance and size. Even health professionals do this.

So the work of the Lancet Commission on the Definition and Diagnosis of Clinical Obesity is likely to become an important milestone in obesity care. Francesco Rubino and the commission’s steering committee published a description of their task in the Lancet Diabetes and Endocrinology on Friday.

Another False Dichotomy

Right from the start, the commission brings us valuable insight by debunking an insidious and false dichotomy. More wasted energy than you might imagine goes into arguments between people who insist that obesity is only a risk factor for other diseases and others who insist that the mere presence of adiposity above a fixed threshold defines a diagnosis of obesity.

It’s one of many false dichotomies that plague people who study obesity and care for the those who have it. Rubino et al explain the fallacy of it and the importance of the commission’s work:

“In our opinion, the question of whether obesity is a disease or merely a condition conveying risk for future ailments is ill conceived because it presumes an implausible all-or-nothing scenario, in which obesity (ie, excess adiposity) is either always or never a disease. Logic and evidence suggest that obesity can be both a risk factor and, sometimes, a disease in and of itself.

“The BMI thresholds used for the definition of obesity have been intended and studied as predictors of future disease or mortality, but not as measures of existing illness.

“Perhaps most importantly, a clinical definition of obesity based on distinctive clinical manifestations that reflect the impact of excess adiposity per se on normal functioning of organs and the entire individual is still missing.

“Hence, a crucial step toward resolving this controversy is to propose a definition for clinical obesity.”

The Attractive Nuisance of BMI

For two centuries now, BMI has been both useful and problematic. It’s useful because it is offers a very easy surrogate for adiposity. For epidemiologists, it may be the best way to develop estimates for the prevalence of obesity in a population.

But it does not suffice for a clinical diagnosis of obesity. Health risks at a given BMI value can be different in different populations. This leads some people to make sensational claims that BMI is an artifact of racism or sexism.

Expertise in the Lived Experience of Obesity

We note that the commision has thoughtfully decided to build the lived experience of obesity into their work. Vicki Mooney of ECPO and Joe Nadglowski of OAC are both working members. Nadglowski told us:

“Knowing that the commission’s work will reflect scientific, clinical, and human expertise gives me confidence that it will produce a valuable result.”

Click here for more on the commission’s work from Lancet and here for the full roster of its members.

Escaping Criticism, painting by Pere Borrell del Caso / Wikimedia Commons

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March 5, 2023