BMI looks like a poor measure of health
Millions considered overweight or obese are OK by other measures, study says.
Millions of Americans who are labeled as obese or overweight according to their body mass index are — when you take a closer look — actually healthy, a new UCLA study indicates.
The f indings, published in the International Journal of Obesity, show that employers could potentially saddle people with unfairly high health insurance costs based on a deeply f lawed measure of actual health.
“This should be a f inal nail in the coffin for BMI,” said lead author A. Janet To- miyama, a psychologist at UCLA.
Body mass index is calculated by dividing a person’s weight in kilograms by the square of the person’s height in meters. According to the Centers for Disease Control and Prevention, a “healthy” BMI is 18.5 to 24.9, an overweight BMI is 25 to 29.9 and an obese BMI is 30 or higher. The calculation has been seen as a slightly more nuanced way to measure health than weight alone.
But over time, researchers have begun to suspect that people with supposedly healthy BMIs can be very unhealthy, and those with high BMIs can actually be in very good shape.
“The public is used to hearing ‘ obesity,’ and they mistakenly see it as a death sentence,” Tomiyama said. “But obesity is just a number based on BMI, and we think BMI is just a really crude and terrible indicator of someone’s health.”
That would be a pretty big deal, especially since the U. S. Equal Employment Opportunity Commission recently proposed rules that would allow employers to penalize employees for up to 30% of their health insurance costs if they don’t meet 24 health criteria — which include meeting a specific BMI. If body mass index doesn’t accurately ref lect health, then those with high BMIs could be overcharged for no reason.
To find out whether BMI is correlated with actual markers of health, a team of UCLA researchers analyzed data from 40,420 people who participated in the 2005- 2012 National Health and Nutrition Examination Survey. They looked at subjects’ blood pressure, triglycerides, cholesterol, glucose, insulin resistance and C- reactive protein data — markers that are linked to heart disease and inf lammation, among other issues.
They found that nearly half ( 47.4%) of the overweight people and 29% of obese people were, from a metabolic standpoint, quite healthy. On the f lip side, more than 30% of those with “normal” weights were metabolically unhealthy.
“The reason I think people rely on BMI is because it’s easy; if you know someone’s weight and you know someone’s height, then out pops this magical number,” Tomiyama said. “But getting blood pressure is pretty easy too. It takes maybe 20 seconds if you have the machine. And so I really think focusing on better health markers like blood pressure is a better way to go about it — particularly when we’re talking about f inancial penalties.”
The results showed that using BMI as the primary indicator of health means that 74.9 million adults in the U. S. are being miscategorized as healthy or unhealthy. ( That includes the 34.4 million people who are considered overweight and the 19.8 million considered obese according to BMI.)
“Policymakers should consider the unintended consequences of relying solely on BMI,” the authors wrote in the study, “and researchers should seek to improve diagnostic tools related to weight and cardiometabolic health.”