When Adolphe Quetelet published Sur l'homme (On Man) in 1835, he was not concerned with treating patients. The Belgian astronomer and statistician was attempting to extract a type he called the "average man" from the height and weight records of thousands of individuals. He was the one who observed that adult weight increases roughly with the square of height.1

The ratio was named 137 years later by American physiologist Ancel Keys. In 1972, Keys and his team compared data from 7,424 healthy men across 12 groups in five countries. They termed the division of weight by the square of height the "body mass index," preferring it over other ratios because it was easy to calculate and could be applied to any population.2

What is in this article?
  • We explain how the body mass index originated from an astronomer's population calculations rather than a physician's clinic.
  • We unpack why two people with the same height and weight can carry vastly different health risks.
  • We detail which metric stood out for specific diseases in a comparison involving 4.26 million people in China.
  • We outline the limitations of measurements that can be taken at home with a simple tape measure.

How did an astronomer's ratio become a medical standard?

Ancel Keys favored the metric because it proved useful in population research. The formula contains only two numbers: weight and height. It does not separate muscle from fat or waist from hips.

National statistics continue to rely on this simplicity today. According to the 2022 Turkish Health Survey, the body mass index (BMI) calculated from height and weight classified 20.2 percent of the population aged 15 and older as obese. The rate was 23.6 percent for women and 16.8 percent for men. In the same survey, 40.4 percent of men and 30.9 percent of women fell into the "pre-obese" group.3

Why do two bodies with the same BMI carry different health risks?

The obesity commission of the journal The Lancet Diabetes & Endocrinology wrote in a report published on January 14, 2025, that BMI sometimes underestimates and sometimes overestimates body fat.4 An athlete with high muscle mass can have a BMI that reaches the obesity threshold, while someone with accumulated visceral fat around their abdomen can remain within the normal range.

The commission included 58 experts, and their recommendations received endorsement from more than 76 scientific societies and patient organizations. According to the report, BMI should be used solely for population-level risk estimation, research, and screening, rather than single-handedly describing an individual's health. Excess fat must be verified either by direct measurement or by adding at least one body measurement to BMI: waist circumference, waist-to-hip ratio, or waist-to-height ratio. For individuals with a BMI above 40, excess fat can be accepted without requiring additional measurements. The commission also distinguished between two conditions. "Clinical obesity" is a disease state where excess fat impairs organ function or daily movement, whereas "pre-clinical obesity" is a period where organs still function normally but risk is elevated.4

We previously covered the link between waist circumference and heart risk based on a cohort of approximately 260,000 individuals.

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Which metric performed best in a study of 4.26 million people?

One of the largest comparisons investigating whether a single number could replace BMI was published in October 2026 in the journal Science Bulletin. A team led by Yi Wu, Limei Nie, and Yue Cai utilized the records of 4,258,033 adults aged 35 to 75 who participated in the ChinaHEART cohort between November 2014 and December 2023. Participants hailed from 31 provinces of mainland China and were followed for a median of 4.9 years. Death or first hospital admission for each disease counted as an event.57

The 15 evaluated metrics were divided into three groups. The first group included ratios calculated using only a measuring tape and a scale, such as waist-to-height ratio, body roundness index, and body shape index (ABSI). The second group estimated visceral fat. The third group relied on blood values: the triglyceride-glucose index (TyG), calculated from fasting triglycerides and fasting blood glucose, is considered an indirect indicator of insulin resistance. The research team combined this index with body measurements and tested six separate derivatives.5

Most of the metrics showed that as values increased, the risk of cardiovascular disease and diabetes also rose. The relationship was weak for cancer and chronic obstructive pulmonary disease (COPD), showing a flat curve in some metrics and an inverse relationship in a few. The metric that relatively best discriminated cardiovascular events was the Chinese visceral adiposity index (CVAI). This index is calculated from age, BMI, waist circumference, triglycerides, and HDL cholesterol, and was developed specifically for the Chinese population.6 For diabetes, the TyG index stood out, while ABSI stood out for COPD. None of the 15 metrics clearly discriminated risk in the case of cancer.5

Notes and Sources

  1. Eknoyan, G. (2008). "Adolphe Quetelet (1796-1874): the average man and indices of obesity". Nephrology Dialysis Transplantation, 23(1), 47-51. DOI ↩
  2. Keys, A., Fidanza, F., Karvonen, M. J., Kimura, N. and Taylor, H. L. (1972). "Indices of relative weight and obesity". Journal of Chronic Diseases, 25(6-7), 329-343. DOI ↩
  3. Turkish Statistical Institute (2023). "Turkey Health Survey, 2022" press release (June 1, 2023) and Turkey Statistics 2022. tuik.gov.tr ↩
  4. Rubino, F., Cummings, D. E., Eckel, R. H. et al. (2025). "Definition and diagnostic criteria of clinical obesity". The Lancet Diabetes & Endocrinology, 13(3), 221-262. DOI ↩
  5. Wu, Y., Nie, L., Cai, Y. et al. (2026). "Associations of body shape, visceral adiposity, and metabolic function indices with risk of major noncommunicable diseases: evidence from a nationwide population cohort". Science Bulletin. DOI ↩
  6. Xia, M. F., Chen, Y., Lin, H. D. et al. (2016). "An indicator of visceral adipose dysfunction to evaluate metabolic health in adult Chinese". Scientific Reports, 6, 38214. DOI ↩
  7. Science Bulletin press release (October 2026). "Beyond BMI: A study comparing the ability of different obesity indices to identify risks for major chronic diseases". brightsurf.com ↩
  8. National Institute for Health and Care Excellence (NICE). Overweight and obesity management (NG246), recommendations 1.9.5, 1.9.14 and 1.9.15; NICE announcement, April 8, 2022. nice.org.uk ↩

This article is for informational purposes only and does not constitute medical advice. Consult your physician for decisions regarding weight and waist measurements. Cover image: Waist measurement at Moody Air Force Base (USA). Photo: US Department of Defense, public domain (Wikimedia Commons).