Is Body Mass Index (BMI) a Reliable Signal of Health?

It’s important to realize that “obese” doesn’t always mean “unhealthy.”

Medically reviewed in January 2022

Body mass index (BMI), a simple ratio of height and weight, has become a shorthand way for doctors and insurance companies to determine if someone is healthy. According to the Centers for Disease Control and Prevention, about one-third of Americans are considered obese by this measure.  

The problem? A 2016 study published in the International Journal of Obesity found that millions of people in the “obese” range are actually healthy in terms of blood pressure, cholesterol, blood sugar and similar tests, while many with “normal” BMIs are worse off. 

So, is your BMI a lie? And can BMI be fairly considered by insurance companies when setting premiums?  

We talked to Matthew Brengman, MD, FACS, a bariatric surgeon at Parham Doctors' Hospital in Virginia to uncover the truth. 

What is your opinion of the study?  Is BMI accurate? 
The study is a little exaggerated, honestly. It accentuates a point that a lot of people have made over the years: BMI is not everything because it’s only as good as your height and your weight. We also know that BMI is not particularly accurate when height and weight are self-reported. And while there is a role for BMI, it’s just not a great indicator for insurance companies to charge people more if they have a higher BMI. 

Bottom line: BMI by itself shouldn’t be making medical decisions, and guess what, we don’t. 

Is  body composition  a better measure of overall health? 
It can be better, but it’s very difficult to do, and body composition is not something that we have accessibility to everywhere. So yes, the percentage of body fat in combination with overall weight is a better measure than weight or BMI alone in predicting morbidity or likelihood to develop disease. 

What could mislabeling a person as obese do to their overall health?  
We shouldn’t ignore BMI, but we also shouldn’t overestimate its value. The misconception is that everyone with BMI of 30 is ill at that moment, and that is not true. This study is just a snapshot in time, but weight has a cumulative effect on health over a period time. For example, a 20-year-old with a BMI of 30 is much less likely to be sick compared to a 50-year-old with the same BMI over the past 30 years. 

The study author said this should be the final nail in the coffin for BMI. Will it be? 
I think that is a pipe dream because we do not have the resources for better testing. If the authors are suggesting that we need to do the battery of tests on every single patient like they did in the study, I would like to see where that money came from. BMI does have value; we just shouldn’t make insurance decisions based on it. 

People are going to still measure BMI. In my field, weight loss surgery, we have been using BMI as one of the major indicators for surgery since 1991, based on guidelines from the National Institutes of Health, and they actually reconvened a few years ago, and still included BMI as one of the measures for weight loss surgery, so there are no nails I don’t think.

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