Opinion | It's Time to Retire BMI as a Clinical Metric – Medpage Today

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Imagine a sales rep comes to your clinic office to pitch a new gadget to gauge your patients’ health. They tell you that it’s not nearly as good as the measures you already have. It performs even worse with older people and athletes. It will drive large numbers of patients away, while it worsens symptoms in others. Then the sales rep adds sheepishly, at least it’s cheap and easy to use.
Would you buy it? Of course not, who in their right mind would?
Except, that is, if that “new gadget” is a body mass index (BMI) calculator. Then buying it is what most of us in the health professions have already done, usually without questioning. And the consequences are dangerous.
The genesis of BMI as a metric dates back nearly 2 centuries to the work of Belgian mathematician (not physician) Adolphe Quetelet, who had the singular idea to create a quick way to approximate body composition in the society. In the 20th Century, BMI was resurrected as a risk prediction tool for insurance companies. Though BMI was never intended as a measure to be applied to an individual’s health, by the 1990s, as panic arose over increasing weights nationwide, Quetelet’s metric — once so obscure that it was known only in the rarefied world of historians of 19th Century mathematics — became a household word. BMI has now become the organizing principle of a massively sprawling surveillance system and the default tool in society’s arsenal in the “war on obesity.”
BMI surveillance is ubiquitous in medical settings and medically focused technologies. BMI is assessed at nearly every touchpoint in primary and specialty care. BMIs are often included in electronic health record work flows even when not relevant. Payors and clinic or hospital quality-improvement policies incentivize clinicians to assess, categorize, and intervene upon BMI at most encounters.
Yet, a growing body of research on weight stigma in medicine has identified routine BMI assessments as a key barrier to care for people living in larger bodies and for others experiencing weight-based shame. Studies and patient stories tell us that anticipating being weighed in medical settings leads many to delay or avoid medical care altogether, resulting in missed preventive care or worse. When patients do arrive to care, a focus on BMI can cause more problems than it resolves. Clinicians’ focus on BMI can lead to unproductive weight-related conversations that fracture the doctor-patient relationship and may introduce mistrust. This can lead to patients opting not to follow physician advice, even when that advice is not weight-focused, and not pursuing follow-up care due to faltering trust — a vital element of effective doctor-patient relationships. Additionally, misplaced BMI assessments can unnecessarily divert clinician focus to weight, an easy default but often misguided explanation for various signs and symptoms, and can result in missed diagnoses, sometimes with grave consequences.
BMI as a metric has become so formally entrenched in clinical interactions that it is rarely questioned. Indeed, in many of the instances in which BMI is assessed in medical settings, the information is not pertinent to medical decision making and often not even used. Thus, BMI assessment may be causing risk (e.g., loss of trust, delayed care) while providing minimal to no benefit. This raises a reasonable question: What purpose is served by continued collection of these data even as the very practice of BMI assessment itself negatively affects healthcare access and quality of care? The same question can be asked about the assessment of BMI in many other settings and sectors in which BMI surveillance has been deployed (e.g., life insurance assessments, military physicals, school gym classes, mass marketed online BMI calculators for consumers).
A substantial array of evidence documents the myriad harmful and far-reaching impacts of the “war on obesity” and the weight stigma it has fomented. While attempts have been made to estimate the costs of obesity on the economy, none of these prior studies parsed out how much weight-based stigma or discrimination, as opposed to the adiposity itself, factors into the equation. We did. In a comprehensive study we recently conducted in collaboration with Deloitte Access Economics and Dove, we document for the first time the effects of weight discrimination on the U.S. economy and society. What we found was sobering.
First, weight discrimination is common. We estimated that each year 34 million people in the U.S. ages 10 years and older experience discrimination based on their weight severe enough to have impacts on their health, quality of life, job opportunities, and our economy. Second, weight discrimination is expensive. The total costs associated with weight discrimination were $430 billion in 2019, which included $206 billion in financial costs and $224 billion in lost well-being.
Medical providers and others will surely question what to do if we throw out BMI as a clinical metric. Keep in mind, though, that many, if not most, clinical interactions do not need BMI as an informational input. For example, BMI is not helpful in making a diagnosis of common viruses or strep pharyngitis. Second, BMI does not take into account distribution of fat or muscularity, which can vary substantially across people with the same BMI. As a result, it is an extremely imprecise proxy for individual adiposity and, importantly, not a proxy at all for overall health. In fact, BMI misclassifies a large percentage of individuals as unhealthy when indeed they are metabolically quite healthy. Other measures such as blood pressure may be more helpful.
Weight-inclusive approaches have been offered as alternatives to overly focusing on BMI in clinical encounters. Weight-inclusive approaches instead focus on overall well-being, rather than weight alone, and on health-promoting behaviors that will impact overall health with or without changing BMI. In practice, weight-inclusive counseling is not so different from the more typical weight-focused approaches that so many clinicians have been taught to follow. For example, the weight-inclusive approach often encourages health promoting behaviors such as physical activity or limiting sweetened beverages, but importantly, it does so in an effort to improve overall health without a focus on losing weight or preventing weight gain.
Chances are, if BMI were not already second nature, most of us would be quick to show the door to a sales rep with such a dubious pitch. But now that we know what a faulty metric BMI is, what’s to be done in the immediate term? Before the next time you ask a patient to step up on the scale, consider two simple questions: Is BMI essential in this encounter for medical decision making? Could a focus on weight be a barrier to care or stigmatizing for this patient? If the answer is no to the former or yes to the latter question, try leaving BMI out of the encounter and see if the trust increases and care improves.
S. Bryn Austin, ScD, is professor of social and behavioral sciences at Harvard T.H. Chan School of Public Health, and director of the Strategic Training Initiative for the Prevention of Eating Disorders: A Public Health Incubator. Tracy K. Richmond, MD, MPH, is assistant professor of pediatrics at Harvard Medical School, and director of the Eating Disorders Outpatient Program at Boston Children’s Hospital.
The material on this site is for informational purposes only, and is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider.
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