How BMI Gets it Wrong in Heart Health

When it comes to heart health, millions of Americans who have been labeled obese or overweight aren’t in such bad shape after all, according California researchers.

Writing in the International Journal of Obesity, University of California Santa Barbara doctoral candidate Jeffrey Hunger and colleagues make the case for doing away with body mass index (BMI) as an indicator of cardiometabolic health. The team cites 74 million instances where body mass index gets it wrong.

Long the standard of healthy weight, BMI dates back to an 1832 invention by a Belgian statistician studying probability calculus. What was then called the Quetelet Index was a simple ratio: weight divided by the square of height.

In its modern incarnation the resulting number falls into one of four categories from “underweight” to “obese”. As the US Centers for Disease Control and Prevention (CDC) points out in publications on healthy weight, BMI is invaluable to clinicians and patients alike in part because it is “inexpensive and easy to use”.

Hunger raises the question of whether it is it accurate as a predictor of heart health.

The researchers examined existing data from the last eight years of NHANES, the National Center for Health Statistics’ biggest and most comprehensive national survey.

When profiles of survey respondents flagged as obese or overweight by their BMI alone were juxtaposed with a cardio-metabolic profile including levels of blood sugar, cholesterol, blood pressure, and the like, the numbers did not come close to matching up.

Of those who would be considered unhealthily overweight according to their BMI, almost 50% were by all other indications healthy.

Even more unexpected, about a third of the BMI “normal weight” group showed signs of poor cardiometabolic health.

“Not only does BMI mislabel 54 million heavier individuals as unhealthy, it actually overlooks a large group of individuals considered to have a ‘healthy’ BMI who are actually unhealthy when you look at underlying clinical indicators,” the team wrote.