Research & Education

BMI = Be More Intelligent (When Assessing Health)

“Using BMI categories as the main indicator of health an estimated 74936678 US adults are misclassified as cardiometabolically unhealthy or cardiometabolically healthy.”

That is quite a statement! Certainly not one to be made lightly but the authors of the paper in which it appears Misclassification of cardiometabolic health when using body mass index categories in NHANES 2005-2012 feel that their data concerning the associations—or lack thereof—between body mass index (BMI) and overall health “should be the final nail in the coffin for BMI.” Again not a statement to be made lightly but one that hammers home the absence of automatic and incontrovertible connections between an individual’s health and the effect of Earth’s gravity on their physical body. 

Considering the relative oddness of what BMI measures—an individual’s body weight in kilograms divided by the square of their height in meters—one has to wonder how this managed to become as important as it now is in epidemiological studies. That’s a key word in fact: epidemiological. A measurement like BMI may indeed be useful for helping to identify long-term trends on a population-wide basis but it is quite a poor metric for assessing the health of individuals. Individual patients are not statistics. Laws of averages may not necessarily apply to them and they may fall well outside the standard deviation.

It is crucial for healthcare practitioners to recognize that a patient’s body weight is often misleading. Clinicians are increasingly recognizing that there are individuals who are overweight but otherwise healthy and others who have a “normal” BMI but who are at high risk for cardiometabolic disease. The former are referred to as the “metabolically healthy obese” while the latter are called “normal weight obese” or more colloquially “TOFI”—thin outside fat inside.

In comparing individuals’ BMI to measurements of their blood pressure triglycerides cholesterol glucose degree of insulin resistance and C-reactive protein authors of the study that evaluated the most recent NHANES data determined “Nearly half of overweight individuals 29% of obese individuals and even 16% of obesity type II/III individuals were metabolically healthy. Moreover over 30% of normal weight individuals were cardiometabolically unhealthy.” These findings reinforce NHANES data from 1999-2004 from which researchers concluded “Among US adults 20 years and older 23.5% (approximately 16.3 million adults) of normal-weight adults were metabolically abnormal whereas 51.3% (approximately 35.9 million adults) of overweight adults and 31.7% (approximately 19.5 million adults) of obese adults were metabolically healthy.” It should be noted however that the accuracy and admissibility of NHANES data has been called into question although this has more to do with food frequency and dietary recall than with weight and actual measurements of disease risk.

Based on nothing but BMI individuals who are healthy (but heavy) may be forced to pay higher premiums for health and life insurance than people who weigh less but who are at far greater risk for treatments and procedures that would cost insurers more and present a greater burden to the healthcare system overall. Moreover it’s unfortunate enough that heavier individuals face social stigma and “fat-shaming” in public in person and online. The last place they should encounter it is at their doctor’s office. Too often medical conditions that have nothing to do with carrying a few extra pounds—such as migraine headaches or anxiety—are nevertheless blamed on overweight or obesity. The fear of facing body weight stigma at the doctor’s office goes far beyond a patient wanting to avoid hurt feelings and an emotionally uncomfortable encounter. The stigma of being reduced to a number on a scale may cause overweight or obese individuals to delay or altogether avoid seeking medical treatment for conditions which if treated early are fairly benign and entirely correctable but which if allowed to progress may eventually become much more serious. The “final nail in the coffin for BMI” can come from doctors themselves. Encountering people of all shapes and sizes who experience some of the same health issues regardless of body weight puts physicians in a unique position to help the public—not to mention government authorities and private insurance companies—understand that an individual’s weight is often a poor indicator of how healthy they are.

Adipose tissue is not entirely inert. Like a walkie-talkie it sends and receives and some researchers even call it “an endocrine organ.” Certainly excess body fat is regulated by and in turn regulates cellular signaling molecules that may influence disease processes. But that doesn’t mean that individuals without excess adiposity are free of elevated risk for chronic cardiometabolic illness. Maintaining a “healthy weight” is indeed part of preserving overall health and vitality but data suggests that what exactly a healthy weight is may not be what we think it is.