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BMI — whether ‘obese,’ ‘overweight’ or ‘normal’ — is an unreliable measure of health, study finds

According to the study’s findings, 34.4 million adults in the U.S. who are “overweight,” 19.8 million who are “obese” and 20.7 million who are “normal” may have a health profile that is not reflected by their BMI.

Last year, the Equal Employment Opportunity Commission (EEOC) proposed a new rule that would allow companies to make their employees pay higher health insurance premiums if they fail to meet certain health criteria, including maintaining a healthy body mass index (BMI).

But is BMI an accurate indicator of a person’s current health status or future risk of disease?

Not necessarily, according to a recent study published in the International Journal of Obesity.

The study found that almost one-third of people with an “obese” BMI are cardio-metabolically healthy, and a similar percentage of people with a “normal” BMI are cardio-metabolically unhealthy.

Cardio-metabolic risk refers to the likelihood that you will develop heart disease, type 2 diabetes or stroke.

By using BMI as the main indicator of cardio-metabolic health, say the study’s authors, we may be misclassifying the health status of more than 74 million Americans.

Developed in Minnesota

BMI is calculated by dividing your weight in kilograms by the square of your height in meters. (If you want to avoid doing the math, just use this online BMI calculator provided by the National Heart, Lung, and Blood Institute.) A BMI of 18.5 to 24.9 is considered “healthy.” One from 25 to 29.9 is considered “overweight.” And one at 30 or higher is considered “obese.”

According to the Centers for Disease Control and Prevention (CDC), 69 percent of Americans aged 20 or older are either overweight or obese. 

As I’ve noted in Second Opinion before, the BMI formula was developed in the early 1970s by University of Minnesota physiology professor and obesity researcher Ancel Keys — but only as a tool to help epidemiologists make comparisons between current and historic obesity levels of large populations. Keys did not envision using BMI to determine an individual’s health status.

Study details

For the new study, researchers at the University of California, Los Angeles analyzed data collected by more than 40,000 American adults who participated in the National Health and Nutrition Examination (NHANES) survey between the years 2005 and 2012. The data included the participants’ height and weight — and, thus, their BMI — but also a host of other health-related measures, including assessments for blood pressure, blood glucose, insulin resistance, and triglyceride, cholesterol and C-reactive protein levels. Those latter measures are all markers for cardio-metabolic risk. 

According to the data, about half of the study’s 40,000 participants were overweight and about a third were obese. But when the UCLA researchers looked for a link between BMI and the cardio-metabolic markers, they found that 47 percent of the people with overweight BMIs and 29 percent of those with obese BMIs were healthy. 

“For these individuals, having a healthcare provider prescribe weight loss could be a misuse of time, patient effort, and resources,” the study’s authors write. “Focusing on BMI as a proxy for health may also contribute to and exacerbate weight stigmatization, an issue that is particularly concerning given [that] health providers evince high levels of anti-fat bias.” 

The UCLA researchers also found that 30 percent of people with a normal BMI were, cardio-metabolically speaking, unhealthy.

“When healthcare providers deem these individuals as ‘healthy’ merely because they are not overweight or obese, critical diagnoses could be delayed or missed altogether,” the researchers warn.

According to the study’s findings, 34.4 million adults in the U.S. who are “overweight,” 19.8 million who are “obese” and 20.7 million who are “normal” may have a health profile that is not reflected by their BMI.

EEOC should reconsider

“These results clearly indicate that health policies such as those proposed by the EEOC should not relay on BMI,” the study’s authors conclude. “Not only are such policies discriminatory, but they run the risk of overlooking more effective approaches” — programs, for example, that help people exercise more and develop practical, health-enhancing skills, such as stress management.

“There are healthy people who could be penalized based on a faulty health measure, while the unhealthy people of normal weight will fly under the radar and won’t get charged more for their health insurance,” said A. Janet Tomiyama, an assistant professor of health psychology at UCLA and the study’s lead author, in a released statement. “Employers, policy makers and insurance companies should focus on actual health markers.”

FMI: You’ll find an abstract of the study on the International Journal of Obesity’s website, but the full study is behind a paywall. 

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Comments (4)

  1. Submitted by Susan Lesch on 02/10/2016 - 01:16 pm.

    Credit may be due

    Wouldn’t it be more fair to say that the US National Institute of Health in 1985 pinned BMI to the health of individuals?
    (I’m just reading Jeremy Singer-Vine’s article, linked from your first mention of Ancel Keys in this context. I’m not convinced that Keys and Minnesota deserve quite so much attention.)

  2. Submitted by Russell Booth on 02/10/2016 - 01:46 pm.

    No wonder the Vikings…

    5 Bridgewater, Teddy BMI 27.6 Overweight
    11 Wallace, Mike BMI 27.8 Overweight
    13 Hill, Shaun BMI 28.7 Overweight
    44 Asiata, Matt BMI 29.7 Overweight

    54 Kendricks, Eric BMI 31.5 Obese
    55 Barr, Anthony BMI 30.2 Obese
    71 Loadholt, Phil BMI 37.9 Obese
    73 Floyd, Sharrif BMI 38.9 Obese

    3 Walsh, Blair BMI 24.4 Normal
    18 Locke, Jeff BMI 21.4 Normal

    Only the kickers are healthy. Or the measurement is much too crude. It does penalize muscle mass.

    It’s hard to believe anybody would think BMI is an accurate measure of health. I hope the mission creep of the EEOC does not result in them sanctioning discriminatory practices.

  3. Submitted by Ray Schoch on 02/10/2016 - 07:04 pm.


    When I graduated from high school, I was 6′ 2″ tall and weighed 145 pounds – so my BMI was 18.6. I also had severe asthma, smoked a pack of cigarettes a day despite the asthma, and while farm work had certainly made the label “wiry” an accurate one, I would not have labeled myself as particularly “healthy.” More than half a century later, I’ve shrunk to 6′ 1″ in height, quit smoking 26 years ago, and gained 55 pounds – my current BMI is 26.4. I was diagnosed with Type 2 diabetes last spring, though dietary changes and medication brought about significant changes in the relevant numbers by late last summer, and I go back in 2 weeks to see if those changes have been maintained. Having done lots of reading about diabetes since being told I have Type 2, I’m well aware of the risks and dangers it poses, but despite those negatives, if I had to somehow identify myself right now in health terms, I’d have to say I *feel* healthier at 71 than I was at 16.

  4. Submitted by Joel Stegner on 02/10/2016 - 10:23 pm.

    Weight gain

    Most Americans who have high BMI once had BMI in the normal range and were healthier when they did. What American medicine is not doing is helping people keep the extra fat off. If you weight extra because you are muscular, no problem. Few middle age and older have that much extra muscle. Keep the weight off and slowly lose it by diet and exercise if you are putting it on.

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