ObesityObesity and BMI

Let's Talk About Obesity and Body Mass Index (BMI)

Doctors have long used a measure called Body Mass Index (BMI) to diagnose obesity. Now, experts say there are better ways.

    Our Pro PanelObesity and BMI

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

    Francisco Lopez-Jimenez

    Francisco Lopez-Jimenez, M.D.Chair for the Division of Preventive Cardiology

    Mayo Clinic
    Rochester, MN
    Angela Fitch, M.D.

    Angela Fitch, M.D.Associate Director of the Massachusetts General Hospital Weight Center, Vice President of the Obesity Medicine Association

    Boston, MA
    Sharon Zarabi, RD headshot.

    Sharon Zarabi, R.D.Registered Dietitian and Bariatric Program Director

    Lenox Hill Hospital
    New York, NY

    Frequently Asked QuestionsObesity and BMI

    How do you diagnose obesity?

    For years, doctors have used a measure called Body Mass Index (BMI) to diagnose obesity. To determine your BMI, you divide your weight (in kg) by your height (in meters) squared. But today, experts say there are better ways to diagnose this ubiquitous condition, including waist circumference; waist-to-hip ratio; and electrical bioimpedance analysis.

    What is the BMI for obesity?

    A BMI of 30 or more is considered obese. Obesity is further divided by class:

    Class 1 = BMI of 30.0 to 34.9
    Class 2 = BMI of 35.0 to 39.9
    Class 3, or severe obesity = BMI ≥ 40.0

    Is BMI a good indicator of obesity?

    Not so much. BMI critics—and there are many—believe it may be a misleading measurement. First, because BMI doesn’t distinguish fat from muscle, bone, or organ, it doesn’t measure body fat percentage, which is strongly linked with a person’s health. Nor does BMI factor in where you carry your weight. Belly fat, or fat that accumulates around the waistline and abdominal organs, greatly heightens one’s risk of heart disease, type 2 diabetes, and other obesity-related complications, as well as death. But a person could easily fall into the “normal” BMI category (18.5 to 24.9) and have a waist circumference that puts him or her in a high-risk health category. There are other criticisms, as well – these are just two.

    What waist circumference is considered obese?

    In men, a waist circumference greater than 40 inches is considered to fall in the obesity range. For women, it’s a waist circumference greater than 35 inches.

    Leslie Goldman

    Leslie Goldman


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