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What is Obesity?


Updated January 07, 2013

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.


We often hear that rates of obesity are increasing in the United States and other industrialized countries, and how avoiding obesity can help your longevity, whether you’re male or female. But how exactly is obesity defined?

According to the U.S. National Institutes of Health, obesity is having too much body fat. The most common way of gauging obesity is through a measure called Body Mass Index, or BMI, which is a ratio of body weight to height. The formula, described by the U.S. Centers for Disease Control and Prevention (CDC), is:

BMI = weight (kg) / [height (m)]²

A BMI of 30 or higher is considered obese.

While BMI assessment has some shortcomings, like not accurately accounting for body composition in very muscular people, it's an inexpensive and readily-available tool to compare a person’s weight with that of the general population. Other more complicated measurements, such as skinfold thickness and bioelectrical impedance, require specialized instruments and expertise to perform, and may therefore be less accessible to the public, according to the CDC.


About BMI for Adults. US Centers for Disease Control and Prevention. Public Information Sheet. Accessed October 23, 2012.

Obesity. US National Institutes of Health Medline Public Information Sheet. Accessed October 23, 2012.

Obesity, Physical Activity, and Weight-Control Glossary. US National Institutes of Health Weight Control Information Network Public Information Sheet. Accessed October 23, 2012. http://win.niddk.nih.gov/publications/glossary/MthruZ.htm#O

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