BMI ≠ Obesity = Excess Adiposity

The trouble people have with a simple definition of obesity is stunning. Obesity is a disease of excess adiposity. In other words, too much adipose (or fat) tissue for good health. You can find this authoritative definition on the website of the Obesity Society — the leading professional society of people who devote their careers to addressing the disease.

You can find plenty of junk definitions, too. The New Oxford American Dictionary describes obesity as “the condition of being grossly fat or overweight.” It’s not medically or scientifically accurate, but it probably reflects how our bias-laden culture defines obesity.

Wikipedia does pretty well, defining obesity as “a medical condition in which excess body fat has accumulated to the extent that it may have a negative effect on health, leading to reduced life expectancy and/or increased health problems.”

Surprisingly, in the recent consensus conference convened by the American Association of Clinical Endocrinologists, participants spent hours debating the best definition for obesity. They ultimately concluded that obesity is a chronic disease, but called for better diagnostic criteria.

The problem lies with BMI or body mass index. BMI is calculated from height and weight. A value over 25 is widely considered to be an indication of excess weight, and a value of 30 is an indication of unhealthy excess adiposity — obesity.

BMI is the simplest and most reliable screen we have for obesity. But it’s only a screen. It’s not the definition of the disease. Just like any disease, diagnosis of obesity requires a complete clinical assessment. It’s not just a number on the scale. It requires an understanding of the whole person — their metabolic health, functional health, and quality of life. People can have clinically significant obesity at a BMI below 30. And people who are completely healthy can have a BMI of 30 or higher. Such cases are not typical but they are possible.

The definition of obesity is simple — excess adiposity. Diagnosis is more involved.

Click here for the definition of obesity from the Obesity Society. Click here for information on Edmonton Obesity Staging System. And click here for a summary of the AACE Consensus Conference on Obesity.

Not Equal, photograph © Antony Theobald / flickr

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