Upon graduating from university, my excitement for my first job as a field geologist was palpable. Even the required physical assessment carried a certain thrill, that is, until the examining doctor reviewed my chart. He promptly informed me I needed to lose between 10 and 15 pounds. His justification was my Body Mass Index (BMI), which situated me squarely in the “overweight” category. Despite this supposed health concern, he acknowledged that every other test yielded pristine results: my heart was robust, my blood markers were beyond reproach, and my risk profile for disease was comfortably below average. Left alone in the examination room, I was caught between shame and disbelief. I had arrived feeling confident in my body, only to be told by a medical professional that my perception needed a radical overhaul. I adhered to his advice throughout my twenties, pursuing a “healthy” BMI through disordered eating patterns. It was only considerably later that I discovered the doctor’s assessment was fundamentally flawed. He had, in fact, interpreted my chart accurately, but BMI itself had failed to provide a true reflection of my health.
My experience is far from isolated; many individuals have been inaccurately categorized as unhealthy. BMI, a calculation derived by dividing a person’s weight by their height squared to estimate body fat levels, is deeply entrenched within the healthcare system. However, this metric demonstrably distorts the health status of numerous individuals, leading to significant and often detrimental consequences.
BMI cut-offs critically influence access to crucial medical interventions. These include knee surgeries, GLP-1 medications, infertility treatments, gender-affirming care, and bariatric procedures, among others. Consequently, individuals falling outside the designated “acceptable” BMI range might be denied necessary medical care. Conversely, patients presenting with high-risk health indicators but exhibiting “normal” BMIs may be overlooked by clinicians.
After three decades as an unchallenged standard, a growing consensus now acknowledges that BMI is an inappropriate measure for individual health assessment. “There is no logic, no medical coherence to using BMI to define a disease. It’s just not suitable,” states Francesco Rubino, a researcher at King’s College London. Simultaneously, an active search is underway for more accurate and nuanced health indicators. More importantly, this paradigm shift is compelling us to critically examine the intricate relationship between health and body size, and to fundamentally re-evaluate our definition of a “healthy weight.”
The Rise and Persistence of BMI
BMI has endured not due to its biological precision, but rather its speed, cost-effectiveness, and simplicity. Originally developed by mathematician Adolphe Quetelet in the early 19th century as a tool for statistical population analysis, BMI was intended to document average height and weight distributions. As rates of obesity began to climb in the 1970s, a study proposed its utility in tracking this trend across large populations. The study found it could be used to track this trend over large populations.
With obesity rates continuing to surge in the subsequent decades, BMI evolved into an increasingly prevalent research instrument. The World Health Organization’s formal recognition of obesity as a global epidemic in 1997 propelled BMI into widespread clinical use as a tool for individual health assessment. Despite early criticisms highlighting its inappropriateness for individual diagnosis, its sheer convenience facilitated its rapid proliferation, establishing BMI as medicine’s default screening mechanism.
Obesity is significantly associated with a range of serious health conditions, including cardiovascular issues, kidney disease, certain types of cancer, elevated blood pressure, and type 2 diabetes. Clinicians sought a rapid method to ascertain when excess body fat might pose a health risk, and BMI appeared to fulfill this role effectively. This measurement assigns individuals a simple numerical value, categorizing those under 18.5 as underweight, between 18.5 and 24.9 as normal weight, over 25 as overweight, and over 30 as obese. However, Rubino argues that a population-level risk assessment tool was never suitable for conversion into an individual diagnostic instrument.
Critiques and Limitations of the BMI Scale
A prevalent critique centers on BMI’s inability to accurately represent fat distribution within the body. It fails to account for the fact that men often accumulate visceral fat around their midsections, surrounding vital organs. This type of fat is demonstrably more harmful than subcutaneous fat, which women tend to store more readily on their arms, buttocks, and thighs. Furthermore, BMI cannot differentiate between muscle mass and fat mass, a crucial distinction that often leads many athletes to be erroneously classified as unhealthy. This was precisely my experience during that startling medical examination. I possessed a naturally higher muscle mass and was an avid trail runner and swimmer. The very physical attributes that contributed to my elevated BMI were, in reality, indicators of my fitness and strength.
Conversely, at the other end of the spectrum, individuals can possess insufficient body fat to maintain regular menstruation. This condition can lead to a host of other health problems, including bone weakness and fragility, cardiovascular complications, and pelvic pain. Yet, according to their BMI, these individuals may still be officially classified as “normal.” This is not an uncommon scenario among female athletes who maintain sufficient muscle mass to remain within the “normal” weight range but lack adequate body fat. BMI functions as a proxy that can too easily obscure genuine indicators of illness.
“BMI is a good metric of volume – if a body is a cylinder. But I’m no cylinder. I have hips, I have curves on my body,” observes Diana Thomas, a mathematician at the United States Military Academy at West Point. “And so to just put a cylinder on me and say, ‘We’re going to use this body measurement from your outside to tell us what’s on the inside,’ seems pretty limited.”
The Lancet Commission and a Call for Reform
Five years ago, Rubino’s growing frustration with BMI prompted him to establish a commission dedicated to re-evaluating the definition and diagnosis of obesity. The commission’s findings were finally published last year as part of a comprehensive report by The Lancet global commission on obesity. Rubino explains that the reliance on BMI created a “catch-22” situation because it was used to diagnose obesity, which is considered a disease, yet it failed to meaningfully reflect an individual’s health status.
The commission’s report advocated for a significant overhaul of current practices. It proposed that, akin to the distinction between pre-diabetes and diabetes, obesity should be classified into two distinct categories: pre-clinical obesity, where fat levels represent a risk factor, and clinical obesity, where it should be recognized as a distinct health condition. Crucially, the report’s authors asserted that BMI alone should not be the sole determinant of obesity status.
The Lancet commission also highlighted another serious deficiency of BMI: the existence of individuals who are classified as overweight yet exhibit no markers of ill health. Over the past two decades, there has been a growing recognition that obesity does not invariably lead to disease. “Some people who carry some extra fat may actually fare better or may not be affected by it, like Queen Victoria, who lived into her 80s and died from unrelated causes,” notes Rubino.
The Lancet’s recommendations were swiftly embraced by over 75 international medical organizations actively involved in obesity research, signaling a profound transformation within the field: BMI is gradually being phased out.
When Does Weight Truly Impact Health?
The intricate relationship between body weight and health is far more complex than a single number derived from a scale or chart suggests. With BMI demonstrably unsuitable for accurate individual health assessment, researchers are actively pursuing superior measurement tools. It is now understood that the location of fat accumulation, rather than its total quantity, serves as a more robust predictor of health outcomes. Individuals with high levels of visceral fat face more than double the risk of heart disease and exhibit increased probabilities of developing high blood pressure and type 2 diabetes. They are also three times more likely to develop dementia by their mid-to-late seventies.
Consequently, the Lancet commission recommends that healthcare providers ascertain excess body fat through direct measurement whenever feasible, utilizing technologies like bioimpedance devices. These tools employ low-voltage electrical currents to assess body composition. Alternatively, they suggest employing criteria that estimate visceral fat, such as waist circumference, waist-to-hip ratio, or waist-to-height ratio, in conjunction with BMI. Regardless of the measurement tool employed, age, gender, and ethnicity should critically influence the interpretation of results, informed by two decades of evidence demonstrating that these factors significantly impact fat distribution and associated risks.
Various relatively straightforward measurements can provide valuable insights. Sonia Anand, affiliated with McMaster University in Ontario, Canada, points to the landmark INTERHEART study, which initially revealed that waist-to-hip ratio surpasses BMI as a predictor of heart attacks more than two decades ago. Subsequent research has further substantiated its efficacy as a superior indicator of mortality.
Another robust alternative to BMI is the weight-adjusted waist index (WWI). This metric is calculated by dividing waist circumference by the square root of body weight. Unlike BMI, which primarily estimates overall mass, WWI captures central fat storage—a pattern strongly linked to inflammation, hypertension, and cardiometabolic diseases. Its practicality lies in its rapid calculation, requiring only a tape measure and a scale.
Better Ways to Measure Body Fat
Waist-to-Hip Ratio
Divide your waist circumference (measured at the narrowest point above the navel) by your hip circumference. A ratio exceeding 0.9 for men and 0.85 for women is associated with significant health risks.
Weight-Adjusted Waist Index (WWI)
Divide your waist circumference in centimeters by the square root of your body weight in kilograms. A result of 10.4 or higher in men and 10.5 or higher in women indicates potential health concerns.
Body Roundness Index (BRI)
The formula for this index is quite complex. It is therefore most convenient to use an online calculator that incorporates your height, waist circumference, and hip circumference to derive the BRI. A lower score—below 4 in women and 3.5 in men—suggests less fat accumulation around the waist and consequently reduced health risks.
In a study conducted last year involving 239 white women, participants categorized in the highest WWI quartile exhibited significantly elevated levels of visceral fat, higher blood pressure, and increased inflammatory markers compared to those in the lowest quartile, even when their BMIs were comparable. This finding holds particular significance for women, according to Naveed Sattar, a professor of cardiometabolic health at the University of Glasgow, UK. Women generally possess a greater capacity for subcutaneous fat storage, and in women, waist circumference serves as a more accurate predictor of diabetes than BMI. “Where you put your fat matters,” he emphasizes.
Height also plays a crucial role. Taller individuals naturally have larger bone structures and greater muscle mass, factors that BMI does not account for. Over a decade ago, Thomas, driven by her background in mathematics and her personal experiences as an athlete critical of BMI, decided to develop her own metric. She recognized the need for “more math” in health research and questioned the accuracy of prevailing nutritional and health advice.
Utilizing datasets from over 7,000 individuals, Thomas constructed a model that linked body shape to fat patterns demonstrably associated with health risks. This research culminated in the development of the body roundness index (BRI) formula, which employs height, waist circumference, and weight to model body geometry. Subsequent studies have confirmed that BRI more accurately predicts total and visceral fat compared to BMI or individual waist or hip measurements alone. Furthermore, it allows for the analysis of body shape as a continuous spectrum rather than a dichotomous label.
This nuanced approach means that waist-to-hip ratio, WWI, and BRI are all more effective at identifying metabolic risk factors for conditions such as diabetes, cardiovascular disease, hypertension, and various cancers—all of which are closely associated with abdominal fat accumulation, not just generalized fat. Beyond solely relying on body measurements, physicians can incorporate blood tests to further evaluate an individual’s risk. Sattar notes that testing for liver function, triglyceride levels, and HDL cholesterol is both inexpensive and straightforward.
These alternative metrics have profoundly reshaped my understanding of my own body. My WWI places me in the first quartile, signifying “most healthy.” My waist-to-hip measurements categorize me within the “low risk level” group, and my BRI indicates I am in the healthy zone with “excellent” visceral fat levels. This provides a vastly different and more informative perspective than my initial BMI score.
The Campaign to Discontinue BMI
Beyond misclassifying individuals like myself, evidence accumulated over two decades reveals that BMI also provides a distorted health assessment for entire ethnic groups. BMI was initially devised using metrics derived from studies of white populations. Although research exposing these inherent biases began years ago, the full implications have only recently begun to influence public health policy.
Individuals of South Asian, Chinese, and Black descent tend to develop diabetes at higher rates and at lower BMIs compared to white individuals. While the precise reasons for these disparities remain incompletely understood for Black and Chinese populations, the effect observed in South Asian communities is demonstrably linked to their genetic makeup. Sattar explains that South Asian individuals often naturally possess lower muscle mass and higher fat mass relative to white individuals at the same BMI. They also tend to accumulate fat more rapidly around their central body, particularly in the liver. These insights prompted South Asian countries to become early adopters in challenging the universal application of BMI. By 2022, ten Asia-Pacific nations, including India, Singapore, Sri Lanka, and the Philippines, had established their own distinct BMI thresholds for obesity, featuring lower cut-off points, and integrated additional measurements such as waist circumference.
A portion of the research questioning BMI’s efficacy originated with Anand. “Being a South Asian woman, my family history of early-onset heart disease and diabetes being very prevalent, I was very passionate to try and understand our biological differences,” she shares. She recounts that her initial grant applications to investigate BMI variations across ethnic groups were often dismissed as unimportant and subsequently rejected. Nevertheless, she persisted. Her groundbreaking work ultimately demonstrated that individuals of South Asian and Chinese descent experience cardiometabolic risk at significantly lower BMI thresholds than white Europeans. Furthermore, the metric proves inadequate in predicting risk among Black and Inuit populations.
Nearly two decades after her initial concept, Anand’s research was instrumental in spurring a 2020 update to clinical practice guidelines in Canada. This update ensured both lower BMI cut-offs for South Asian individuals and a recommendation for the consideration of non-BMI measures in obesity evaluations for all demographic groups. Other nations have also begun to adapt their approaches. In 2022, the National Institute for Health and Care Excellence, an independent advisory body in England and Wales, issued new guidance encouraging the routine use of waist-to-height ratio in clinical practice. Critics of BMI, including Rubino, argue that it should never be used in isolation and express hope that the widespread support for The Lancet commission’s findings from organizations such as the World Obesity Federation and the World Health Organization will lead to an end of its solitary use in the UK. In the United States, the American Medical Association declared BMI “imperfect” in 2023, recommending its use solely in conjunction with other health assessments.
In the current landscape of weight-loss medications like Mounjaro and Wegovy, this reassessment holds heightened importance. Pharmaceutical treatments for obesity are presently administered based on BMI cut-offs. In England, GLP-1 treatments are typically restricted to individuals with a BMI of 40 or above for Mounjaro, or 35 and above for Wegovy (both adjusted for ethnicity) in conjunction with multiple obesity-related conditions. Japan reserves these medications for individuals with a BMI exceeding 35, while in the US, the Food and Drug Administration recommends them for anyone with a BMI of 30 or higher, although many insurance providers impose stricter criteria.
With an estimated 1 billion people globally classified as obese according to BMI, Rubino points out that the healthcare system lacks the capacity to treat everyone, and “by the way, not all of the 1 billion need it.” Relying solely on BMI to determine both who is considered to have obesity and who is eligible for treatment introduces significant problems at every stage of the treatment continuum.
Medicine’s comprehension of obesity is unlikely to advance unless the field becomes willing to acknowledge, and indeed embrace, the intrinsic complexity of human bodies. “One of the things I always ask [doctors] is, why does everything have to be easy? My body’s complicated. Embrace that complexity!” asserts Thomas. For myself and countless others whose lives have been impacted by the authoritative stance of BMI, the movement towards shape and distribution-based measures is not about dismissing obesity-related diseases. Rather, it is about recognizing individual biology, ethnic variations, and lived experiences. The burgeoning scientific evidence points to a fundamental truth: health is not defined by a single number, and human bodies are far from being interchangeable cylinders.