What is BMI?

For decades, body mass index (BMI) has been considered one of the most important numbers in medicine. Doctors use it. Insurance companies use it. Researchers use it. It can influence eligibility for medications, surgeries, fertility treatments, and even organ transplants.

BMI is calculated using a simple formula that divides weight by height, producing a single number between 10 and 65. According to online calculators and reference charts, if you fall between 19 and 24, your BMI is considered healthy; between 25 and 29, overweight; and 30 or higher, obese.

That's it. No body-fat measurement. No distinction between muscle and fat. No assessment of metabolic health, inflammation, fitness, or where fat is stored in the body.

And yet, this single number has become one of the dominant tools in modern medicine for classifying body size and assessing health risk.

However, with allegations of racism and sexism accompanying the rise of more accurate diagnostic methods, this antiquated measurement equation seems to come under fire more and more each day.

Is it time for us to admit, once and for all, that BMI has been debunked?

How BMI took over the world

The origins of BMI are surprisingly non-medical. The formula traces back to the 1830s, when Belgian mathematician and statistician Adolphe Quetelet attempted to define the characteristics of the "average man" using measurements collected largely from European men. He was not trying to diagnose obesity or measure wellness at the individual level.

BMI later gained traction in the 1970s when physiologist Ancel Keys promoted it as a simple population-level estimate of body fatness. Even then, it was understood to be a rough statistical tool - not a comprehensive health assessment.

Still, simplicity is powerful. And it was this simplicity and ease of use that drove BMI's widespread adoption in public health and clinical settings. It required no bloodwork, no imaging, no expensive equipment, and no specialized training. Public health agencies could rapidly apply it across enormous populations. Insurance companies could use it to estimate risk quickly. Researchers could use it to study links between body size and disease.

And importantly, BMI does correlate with health risk at the population level.

A BMI above 30 is associated with increased rates of:

• Type 2 diabetes
• Cardiovascular disease
• Hypertension
• Sleep apnea
• Osteoarthritis
• Certain cancers
• All-cause mortality

This population-level association explains why many experts argue that BMI remains a valuable screening tool. But population-level statistics are not the same thing as an accurate individual diagnosis. And it's in this gap between population data and individual diagnosis where much of the criticism begins.

The major problems with BMI

BMI cannot distinguish muscle from fat

One of the biggest flaws of BMI is that it treats all body weight the same. Muscle is denser than fat, which means muscular athletes like Tom Brady (BMI 27.4) and LeBron James (BMI 26.8) can easily fall into the "overweight" or "obese" BMI categories despite having low body-fat levels and excellent metabolic health.

BMI can miss metabolically unhealthy people

Ironically, the opposite problem may be even more concerning. A person can have a "normal" BMI while carrying dangerous amounts of visceral fat—the deep abdominal fat surrounding internal organs. This phenomenon is sometimes called normal-weight obesity or "skinny fat." These individuals may appear healthy by BMI standards while still having insulin resistance, fatty liver disease, elevated blood pressure, chronic inflammation, and poor metabolic health. ​

BMI does not work equally across different populations

Another major criticism is that BMI was largely developed using data from white European populations and does not translate perfectly across ethnic groups, sexes, and ages.

For example:

• People of Asian descent often develop metabolic disease at lower BMIs.
• Polynesian populations may carry more lean mass at higher BMIs.
• Women naturally have more body fat than men.
• Older adults often lose muscle mass while maintaining body weight.

BMI can contribute to stigma and delayed care

According to critics, a strong reason to move beyond the use of BMI is that it can contribute to discrimination and harmful medical experiences. This can damage trust between patients and clinicians, contribute to weight stigma, and even delay medical care.

Some patients report avoiding doctor visits altogether because they fear being reduced to a number on a scale. Researchers have also argued that doctors may sometimes overlook unrelated medical conditions by assuming symptoms are caused by body weight.

This does not mean weight is irrelevant to health, or that obesity is not a major global health concern. But it does mean that over-reliance on BMI might oversimplify a far more complicated picture.

Why visceral fat matters more than weight

Modern obesity science increasingly focuses less on total body weight and more on body composition and fat distribution.

Visceral fat, the fat stored around organs inside the abdominal cavity, appears particularly dangerous because it is metabolically active and strongly associated with inflammation, insulin resistance, cardiovascular disease, and fatty liver disease. This is one reason waist circumference and waist-to-height ratio, alternative metrics to BMI that hint at the presence of harmful visceral fat, are gaining traction.

A 2012 systematic review found that the waist-to-height ratio was a better predictor of cardio-metabolic risk than BMI.

And unlike BMI, even a simple waist measurement can provide at least some insight into abdominal fat distribution.

The science is shifting beyond BMI

The medical world is not abandoning BMI entirely, but it is becoming more cautious about how it is used.

A growing number of researchers now advocate combining BMI with:

• Waist circumference
• Waist-to-height ratio
• Body-fat percentage
• Blood pressure
• Blood glucose and A1C
• Cholesterol and triglycerides
• Fitness and activity levels
• Body composition scans

Some newer technologies, such as bioelectrical impedance analysis (BIA) and the gold standard, dual-energy x-ray absorptiometry (DEXA) scans, attempt to directly estimate body-fat percentage and lean mass rather than simply making a mathematical calculation to estimate in that direction.

A major 2025 Lancet Diabetes & Endocrinology Commission review proposed moving beyond BMI alone when diagnosing obesity, recommending the inclusion of direct body-fat measurements or additional anthropometric markers whenever possible.

This reflects a broader shift in medicine away from one-size-fits-all metrics and toward more individualized risk assessment.

So… has BMI actually been debunked?

Not entirely. BMI still works reasonably well as a quick, inexpensive population-level screening tool. In large studies, it remains useful for identifying broad associations between body size and disease risk.

But the idea that BMI alone can define someone's health has almost completely fallen apart. Two people with the exact same BMI can have dramatically different levels of muscle mass, visceral fat, metabolic health, fitness, inflammation, and overall disease risk.

Its convenience and ease of use fueled the rise of BMI. Its decline, in turn, reflects a growing pursuit of precision in assessing health for every individual.

Almost two hundred years later, modern health science is recognizing that metabolic health is more complicated than a single number generated from height and weight.

Frequently asked questions

Is BMI completely useless? No. BMI still has value as a quick population-level screening tool. The main criticism is that it is often overused as an individual measure of health.

Why do we still use BMI? Even though it's generally considered an outdated tool, body mass index remains a quick, inexpensive way to get a ballpark figure for body fat. Since its use has become a matter of habit for insurance companies, public health policy, and clinical guidelines, reducing reliance on it won't happen overnight.

What is more important than BMI? Many experts now emphasize waist circumference, body-fat percentage, metabolic markers, blood pressure, fitness, and overall lifestyle habits as more accurate, more respectful of individual differences, and more predictive measures of health risk.

Can you be healthy with a high BMI? Yes. Depending on factors such as body composition, metabolic health, fitness, and fat distribution. Muscular individuals, for example, may have elevated BMIs without excess body fat.

Can you have a normal BMI and still be unhealthy? Absolutely. Some individuals with "normal" BMI carry excess visceral fat and may still have insulin resistance, fatty liver disease, high blood pressure, or poor metabolic health.

What might replace BMI in the future? Increasingly, researchers are exploring body-fat percentage measurements, waist-to-height ratio, body composition analysis, and metabolic biomarkers as more accurate alternatives or complements to BMI.