Body mass index on the scale

The concept of body mass index (BMI) was created almost 200 years ago and has since been widely used in both research and clinical practice. Certain treatments and medications may only be available if the patient’s BMI is above or below a specific threshold, and when BMI is high, physicians often recommend weight management and normalization of BMI to reduce health risks. But can a single number define a person’s health? That is how BMI is often interpreted, and perhaps why it sparks more debate than most other health measures.

The history of BMI

The concept of BMI was developed in the 1830s by Belgian statistician Adolphe Quételet, who sought to define the characteristics of the “average man”. He observed that a person’s weight does not increase linearly with height but roughly with the square of height, leading to the formula: weight (kg) / height^2 (m^2). Originally, BMI was not intended as a measure of health or wellbeing; it was a demographic observation describing the nonlinear relationship between height and weight.

In the early 20th century, American insurance companies began using height-weight relationships to assess mortality risk, leading to the first “ideal weight tables”. However, BMI gained its current meaning and the name only in the 1970s, when U.S. nutrition researcher Ancel Keys found that BMI correlated with body fat percentage. It was not until the 1990s that the World Health Organization (WHO) and the U.S. National Institutes of Health (NIH) officially adopted BMI for population monitoring and clinical criteria.

Benefits and limitations

The popularity of BMI has its reasons: it is simple and quick to calculate and requires no laboratories or special equipment. It is also easy to understand.

However, its simplicity is also its weakness. It does not account for muscle mass, body fat distribution, or ethnic differences. For example, an athlete may be classified as overweight by BMI despite having a low body fat percentage. Conversely, a lean person with significant visceral fat around the internal organs may fall within the “normal” BMI range, even though such fat is particularly harmful to cardiovascular health.

Since BMI thresholds were originally based largely on white European men, they may not be directly applicable to other populations. For example, Japanese individuals may experience elevated metabolic risk at lower BMI values (ref). BMI also cannot be used as-is for children, whose body proportions differ from those of adults and change over time.

What other measures exist?

There are several alternatives: waist circumference, waist-to-hip ratio, and waist-to-height ratio better capture visceral fat, which is especially detrimental to cardiovascular health. Body fat percentage can be estimated through skinfold measurements or bioimpedance devices. Recent research suggests that neck circumference may be a useful health indicator (ref). Other emerging indices, such as the Body Roundness Index (BRI), attempt to account for body shape and fat distribution, though they tend to be more complex and less practical in clinical settings.

BMI in population health studies

In large-scale population health studies, BMI has long been a central measure. Height and weight are almost always available, even in older datasets, enabling cost-effective analysis of long-term trends and comparisons between populations or demographic groups. BMI has played a key role in monitoring the global obesity epidemic (ref) and in studying its comorbidities and associated mortality (ref). In today’s vast datasets, often including millions of participants, BMI consistently reveals strong links to health: both low and high BMI are associated with the risk of several diseases (ref).

Summary

Despite its well-known limitations, BMI remains a valuable tool in population research. Since “Arnolds” are rare on population scale, BMI works well for identifying large-scale trends or studying the link between obesity and morbidity. However, its limitations must be recognized. In individual risk assessment, BMI should be complemented with other measures to gain a comprehensive understanding of overall health.

Author:

Eeva Sliz