March 2022

THE BIG PROBLEM WITH BMI

This simple number carries a lot of weight, but research shows it’s not a good indicator of your health.

Body mass index (BMI) is foundational in healthcare around the world today.  The simple equation of weight relative to height may be used to determine your risk for certain diseases, your insurance premiums and even whether you qualify for certain medical procedures.  But researchers have been questioning the value of BMI in individual health assessment for a while now, and more recently, body-positivity advocates have implicated its contributing role in weight bias and racism in healthcare, which has more people than ever asking: Should we use BMI at all?  This formula, used as a proxy for body fat, was actually never intended to measure individual health.  It was developed in the early 1800s to study weight variations across entire populations.  BMI is a rigid number based on old data.  And it’s far from perfect in terms of the cutoffs designed to indicate risk.  Individuals may often be miscategorized as unhealthy or healthy based on their BMI alone.  Nearly half of people considered overweight and 29% of those categorized as obese are actually metabolically healthy, meaning their blood pressure, cholesterol, and blood glucose were all normal. Meanwhile, 30% of those considered “normal weight” had metabolic or heart issues.  Part of the problem is that BMI can’t differentiate between weight from fat and muscle.  So, bodybuilders and elite athletes with high muscle mass may be categorized as obese.  And even among people who do have higher body fat, BMI doesn’t tell physicians anything about how it’s distributed, a key connection to disease risk.  Subcutaneous fat around the hips, thighs and buttocks is not as dangerous or as tightly linked to conditions like heart disease and type 2 diabetes as visceral fat in the abdomen.  Further, BMI cutoffs are largely based on data from Western populations, predominantly Caucasian males, making it problematic to apply this measurement to the diverse US population. There is growing evidence that that body composition varies between race and ethnicities. A study in the journal Obesity showed that, for black adults in the US, having a higher BMI (25 and over) did not carry the same risk of death as it did in white adults. And there is also research indicating that people of Asian descent tend to have more body fat, and particularly visceral fat, compared to other racial and ethnic groups with the same BMI, putting them at an increased risk of type 2 diabetes, hypertension and cardiovascular disease at a lower BMI.  Some experts argue that the cutoff for normal weight in Asian and South Asian groups should be set as low as 22.

Leaning too heavily on BMI can prevent good, individualized patient care.  For instance, some procedures, like bariatric surgery, may only be covered by insurance for people above a certain BMI, even if someone’s doctor has determined that they’re otherwise a good candidate.  Regardless of the BMI category you fall into, it’s important to find a doctor who will go beyond the number to get a holistic picture of your health.  Because despite the stigma that people with a higher BMI have a greater risk for a number of diseases than thinner people the research shows it’s not that simple. 

Donavyn Coffey