The Battle of BMI

Is body mass index (BMI) the best way to tell if you are an ideal weight or even healthy? BMI measures your body fat. It uses your weight and height to come up with a BMI number. Using this number, you and your doctor can tell if you might have a weight problem.

Many people, even those who are in shape, take issue with BMI. They say it doesn’t tell the whole story. Age, gender, and muscle mass are just some of the factors that can affect an accurate measurement of body mass index.

Although doctors and dietitians widely use BMI to identify possible weight problems in adults, the measure has come under attack  as a reliable health indicator. It may not provide an accurate measure of body fat for several reasons. 

Some of these reasons include:

• It doesn’t consider sex, bone structure, fat distribution, or muscle mass. Specifically, it doesn’t discriminate between fat and muscle, so a thin person with a lot of muscle can have a high BMI score.
• It ignores changes due to age. Body fat often increases as you get older, while muscle mass decreases. Your BMI may not change over the years even if you have more fat than you did when you were young.

There are other ways to see if you’re overweight or obese:

• High-tech strategies such as skin-fold thickness, underwater weighing or a fat-muscle-and-bone scan measure body fat directly.
• Waist size is also a good measure. Men with a waist circumference of more than 40 inches and women with a waist size of more than 35 inches are considered overweight.

How Can You Lower Your BMI?

If your BMI shows that you are overweight or obese, you can lower it. Follow three simple steps:

• Eat healthy. Choose balanced meals and avoid foods with high saturated fat. Try to eat five or more servings a day of fruits and vegetables. Watch portion sizes. One serving of cereal should be about the size of your fist. One serving of meat should be the size of a deck of cards. One serving of low-fat cheese is about the size of four dice.
• Exercise. Just 30 minutes of moderate activity most days of the week can make a big difference. You don’t have to hit the gym. You can walk, swim or even dance. Just keep moving!
• Get enough rest. Sleep is an important part of good healthy. Getting enough sleep can help prevent the onset of diabetes, obesity and other diseases. If you have a chronic condition, sleep can help you manage it better. Adults should get seven to eight hours each night.

Want to Know Your BMI?

To find your BMI, use one of the many BMI calculators available online. A normal, healthy BMI is between 18.5 and 24.9 for most adults. Although it may not be a perfect way to assess weight, it still offers an important starting point to have a conversation with your doctor.

What do you think? Is BMI a good measure of health? Tell us in the comments!

Sources: AMA: Use of BMI Alone Is an Imperfect Clinical Measure,  American Medical Association, 2023; Mayo Clinic Q&A: BMI Is Not the Only Indicator of Your Overall Health,  Mayo Clinic News Network, 2019; Healthy Weight,  Centers for Disease Control and Prevention, 2022

Originally published 8/4/2016; Revised 2021, 2023