Beyond the Number: Why Public Health Should Rethink Use of BMI

Body mass index (BMI) does not tell us who is healthy. Many people treat BMI as a quick indicator of health and a marker of chronic disease risk, so it often shapes how clinicians, insurers, and patients think about bodies. BMI is a screening ratio that compares weight to height among adults. It does not measure body fat directly, it cannot separate fat from muscle, and it cannot show where fat is stored. When BMI drives decisions about care and coverage, it can reinforce stigma and deepen inequities that public health is supposed to reduce.

Misuse happens when people let that ratio drive care decisions. Once a BMI category becomes a label, it carries the legacy of its creators and of how institutions use it. This is where BMI stops being a neutral measurement tool. These legacies are historical, clinical, and political. In the 1800s, mathematician Adolphe Quetelet created a formula to describe “the average man,” using data drawn mostly from White, European men. Race scientists and eugenicists later used body size to support false claims about normalcy and worth. Insurance companies and public agencies then turned size categories into standards that shaped research and eligibility for services. This context matters because tools inherit the priorities of the systems that use them.

Some clinics and insurers use BMI cutoffs as a gatekeeper for care, especially for surgery and fertility treatment. In orthopedic care, a patient may be told they need to lower their BMI before a joint replacement, even when their pain, mobility limits, and X-ray findings show they need surgery. The intent makes sense. Higher body weight can raise anesthesia and wound risk, and surgeons want to lower preventable complications. The problem is that BMI is a rough screening tool, not a direct measure of surgical risk. It does not capture fitness, blood sugar control, smoking status, cardiovascular health, or functional status, which often predict outcomes more clearly. A hard cutoff can delay care for months or years, worsen disability, and reduce activity, which can make weight loss harder, not easier.

A number built to sort bodies still stands between patients and services that prevent disability and death.

Some fertility clinics set BMI limits for procedures because of sedation safety, dosing, imaging quality, and pregnancy risks that rise with certain conditions. Used carefully, BMI can signal when someone needs extra evaluation, such as blood pressure and glucose testing, sleep apnea screening, or an anesthesia consult. Harm starts when the cutoff becomes the final answer. Two patients with the same BMI can have different cardiometabolic and procedural risks. A strict BMI policy can deny people a time-sensitive chance to build a family, especially for older patients or those with diminished ovarian reserve.

BMI also fails as a health risk measure because it cannot separate fat from muscle, and it cannot show where fat is stored. Body fat around the abdomen links more strongly to cardiometabolic risk than fat stored around the hips and thighs. Waist measures and body composition tools show that a “normal” BMI can hide risk, while a higher BMI can mislabel athletes or people with high muscle mass as unhealthy. Population differences matter too. Risk can begin at lower BMI values among many Asian groups. Black populations can have higher BMI at the same body fat percentage. One cutoff can over-label some groups and miss risk in others.

BMI can also operate as a stand-in for social conditions that shape disease risk. Higher BMI can reflect chronic stress, poverty, disrupted sleep, medication use, and food insecurity, all of which affect cardiometabolic health. Research often finds that BMI tracks risk, but it does not explain why the risk exists. When clinicians and insurers treat BMI as the cause, they can miss the conditions driving risk and choose the wrong targets for prevention.

Retiring BMI as a gatekeeper is not about political correctness. It is about accuracy, fairness, and rebuilding trust in health systems.

Despite flaws in its use and interpretation, BMI remains embedded in research and policy because it is a standardized metric that is simple to calculate. This does not mean giving up on using BMI entirely, but including other measures that capture a more comprehensive assessment of health and patient goals, such as waist circumference, waist-to-hip ratio, and body composition. Clinicians can focus follow-up care on blood pressure, glucose, and mobility rather than weight. Insurers can remove BMI cutoffs from coverage rules and base decisions on metabolic risk or function.

Public health aims to help populations receive care that they can trust so they can live longer, healthier lives. A number built to sort bodies still stands between patients and services that prevent disability and death. Retiring BMI as a gatekeeper is not about political correctness. It is about accuracy, fairness, and rebuilding trust in health systems. Progress begins when we stop ranking bodies and start measuring what truly matters for health.

The views expressed here are the author’s own and do not necessarily represent the views of Public Health Post or Boston University School of Public Health.