ObesitySevere Obesity

Let's Talk About Severe Obesity

About 25% of people with obesity fall into the "severe" classification. Here's what that means and how treatment can help.

    Our Pro PanelSevere Obesity

    We went to some of the nation's top experts on obesity to bring you the most up-to-date information possible.

    Robert Eckel, M.D. headshot.

    Robert Eckel, M.D.Past President and Volunteer Medical Expert, Professor Emeritus

    American Heart Association, University of Colorado School of Medicine
    Aurora, CO
    Anna Welcome, M.D.

    Anna Welcome, M.D.Assistant Clinical Professor; Fellow of the Obesity Medicine Association

    Western Michigan University School of Medicine
    Kalamazoo, MI
    Matt Hutter, M.D., M.P.H.

    Matt Hutter, M.D.President; Professor of Surgery; Director

    American Society for Metabolic and Bariatric Surgery; Harvard Medical School; American Society for Metabolic and Bariatric Surgery

    Frequently Asked QuestionsSevere Obesity

    What are the three levels of obesity?

    There are three levels, or categories, of obesity, and they are based on one’s Body Mass Index (BMI). Class 1 includes those people with a BMI of 30.0 to 34.9. Class 2 includes those with a BMI of 35.0 to 39.9. And Class 3, or severe obesity, encompasses those with a BMI of 40 or above. You can determine your BMI by dividing your weight (in pounds) by your height (in centimeters) squared. Multiply that number by 703 and you’ll have your BMI.

    What causes severe obesity?

    Like other classes of obesity, severe obesity is caused by a combination of genetic and environmental factors. For many people, obesity is a result of an imbalance in caloric intake and expenditure: When you consume more calories than you burn through exercise and activities of daily living, you create what is called a positive energy balance that, continued unchecked, can lead to weight gain and, possibly, obesity. Genetics also contributes to many cases of severe obesity, as does access to massive portion sizes, a lack of physical activity, and some medications.

    What is the average life expectancy of a person with severe obesity?

    According to a recent International Journal of Obesity study, individuals who have obesity live 5.6 to 7.6 fewer years than their healthy-weight counterparts. Those with severe obesity are more likely to die 8.1 to 10.3 years earlier.

    What categorizes a person as having severe obesity?

    A Body Mass Index (BMI) of 40 or higher typically categorizes someone as having severe obesity.

    Leslie Goldman

    Leslie Goldman


    Leslie Goldman is a health and wellness writer who regularly contributes feature stories and essays to various publications.