BMI was never designed to measure health. And in many situations, it can be misleading.

For decades, Body Mass Index, or BMI, has been one of the most widely used numbers in medicine. It is used to classify millions of people as underweight, normal weight, overweight, or obese.

Today, BMI plays an even larger role. In many cases, it determines eligibility for GLP-1 medications used for weight loss.

In reality, BMI was never designed to measure health. And in many situations, it can be surprisingly misleading.

At Fitnescity Health, these limitations are evident across DEXA scans performed across our network of 1,000+ locations.

BMI Was Never Designed as a Health Metric

BMI was developed in the 1830s by Belgian statistician Adolphe Quetelet.

Its purpose was not medical diagnosis. It was a statistical tool used to study patterns across populations.

It was never intended to assess the health of individual people.

Over time, however, BMI became a convenient way to categorize weight in clinical settings. Today it is embedded in medical guidelines, research studies, and insurance policies.

BMI Can Misclassify Health Risk

One of BMI’s biggest limitations is that it cannot distinguish between muscle and fat. This is often illustrated with athletes, who can be classified as overweight or even obese despite having low body fat and high levels of fitness.

But the more important issue is less visible. Across tens of thousands of DEXA scans on our platform, we consistently observe individuals with similar BMIs who have markedly different body fat, muscle mass, and metabolic risk levels.

Two people can have the exact same BMI and be classified the same way, yet have very different metabolic risk levels. One may have higher muscle mass and lower body fat. Another may have lower muscle mass and higher body fat.

The second individual carries a higher metabolic risk, including insulin resistance and long-term disease. BMI treats them as identical.

BMI also does not account for where fat is stored.

Visceral fat, the fat stored around organs, is strongly associated with higher risks of cardiovascular disease, metabolic disease, and insulin resistance. In practice, we often see individuals with “normal” BMI ranges who nonetheless have elevated visceral fat levels. BMI does not detect this.

BMI Now Determines Access to GLP-1 Therapies

The limitations of BMI are becoming more visible as GLP-1 medications transform the treatment of obesity. Clinical guidelines and insurance policies typically use BMI thresholds to determine eligibility for these drugs.

In many cases, patients qualify if they have:

• a BMI of 30 or higher, or
• a BMI of 27 with certain related conditions.

This means a single number derived from height and weight can determine access to one of the most effective weight-loss therapies ever developed. Yet BMI cannot measure body composition, detect visceral fat, or assess metabolic health.

From what we are observing, the mismatch between BMI and underlying physiology becomes particularly clear in this context. Consider two individuals:

• One has a BMI of 26, but carries high visceral fat and low muscle mass.
• Another has a BMI of 30, with higher muscle mass and a more favorable fat distribution.

Under current guidelines, the second individual may qualify for GLP-1 therapy, while the first may not. Their underlying physiology, however, may suggest the opposite.

As GLP-1 adoption accelerates, these edge cases are becoming more common rather than rare.

Looking Beyond BMI

BMI helped medicine categorize weight across populations. But understanding individual health requires looking deeper than height and weight.

At Fitnescity Health, we see a growing shift toward measuring what BMI cannot capture:

• body composition
• visceral fat
• bone density
• cardiorespiratory fitness

These metrics provide a more complete picture of how the body is changing over time.

As new therapies like GLP-1 medications reshape metabolic care, the need for more precise measures of health is becoming increasingly clear.