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How Reliable is The Diagnosis of Obesity?

While I am on a brief holiday in Berlin, I thought I’d rerun a few earlier posts that discuss the issue of measuring obesity and how such measures may or may not be helpful in obesity management – as many readers may not have seen these posts before, comments are very much appreciated.

The following was first posted on October 31, 2008

As most readers of these pages probably know, the current definition of obesity is based on the body-mass-index, a number, which, in populations, nicely correlates with body fat.

However, as body fat alone is not the entire picture, other indices that include measurements of fat distribution such as waist circumference or wait-to-hip ration have been suggested, along with cut-offs that would help identify, who is “obese” and who is not.

But how reliably can these indices be measured in clinical practice (as recommended in obesity guidelines)?

This question was addressed by Paul Sebo and colleagues from the Geneva University Hospitals, Switzerland, in a paper just published in Preventive Medicine.

In this study, repeated anthropometric measurements were performed by 12 primary care physicians on 24 adult volunteers, men and women, with an average BMI of 28. While inter-observer reliability for weight, height, and derived BMI were excellent (R>0.99), they were unsatisfactory for waist circumference (R=0.92), hip circumference (R=0.76) and waist-to-hip-ration (R=0.51).

With BMI, only 1% of the volunteers were misclassified as overweight or obese, whereas the use of WC and WHR lead to misclassification in 6% and 23% respectively.

Reliability for the measurements improved after a one-hour training in anthropometric measurements, but the proportion who were misclassified remained high for WC (5%) and WHR (9%).

So, apparently, even with “Swiss precision”, anything that goes beyond height and weight is too complicated to reliably classify obesity in primary care.

But the real question here is whether or not ANY anthropometric measurement can reliably detect who is threatened of affected by excess weight (my definition of obesity). I have argued before that BMI, although fine for population studies, is not useful when making individual decisions about patients.

Not only is there a wide range in individual variability in the actual body fat present in individuals of the same BMI, but, more importantly, there is a huge variability on how that excess fat actually affects that individual’s health.

We have recently proposed the Edmonton Obesity Staging System, which we now use to supplement BMI measurements with stages that reflect the degree of comorbidity and/or reduction in functional status attributable to the excess weight.

Blindly basing decisions to treat or not-to-treat on BMI alone will result in treating a lot of people who have little to gain, while missing out on many who are clearly threatened or affected by excess body fat.

Edmonton, Alberta


  1. Yes, I know I always have to be contrarian, but tracing everything back to “obesity” (however you define it) is problematic. Just as an example, here’s your definition of stage one obesity:

    Stage 1: presence of obesity-related sub-clinical risk factors (elevated blood pressure, impaired fasting glucose, fatty liver, etc.), mild physical symptoms (dyspnea on moderate exertion, occasional aches and pains, etc.), mild psychopathology, mild functional limitations or mild impairment of well-being

    What if a person with a high BMI has fatty liver, but the doctor blames it on their weight and neglects to ask how much they drink? What if they have aches and pains and the doctor blames it on their weight and neglects to ask about their history of physical injuries? If I were a medical professional, I’m sure I could come up with even more examples.

    And believe me, this is a very real, very pervasive problem with diagnoses that are being made every day. This type of thing has happened to me several times, and many fat people have had much worse experiences with doctors than I have. Not every health problem is related to body size, even in those of us who are large and even if it’s a health problem that has a positive correlation with being large.

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  2. From the post you reference:
    If the presenting condition is largely caused by excess weight (e.g. sleep apnea, type 2 diabetes, hypertension, gastroesophageal reflux disease, etc.) then there is a good chance that weight loss will reverse or “cure” this condition.

    And, there’s the assumption I was talking about, right there in your post. What if the person was formerly thin and had the same symptoms of sleep apnea then? What if type II diabetes runs in the person’s family and thin relatives get it, too? What if the person has high blood pressure because of an extremely stressful job? And gastroesophageal reflux disease? Does that ever have anything to do with weight? It seems more likely that it would be related to eating habits.

    Once a doctor decides that a problem is weight related, they will often fail to ask the right questions, or even fail to listen when the patient brings up this type of information on his own.

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