Body Mass Index (BMI)

Is the Body Mass Index (BMI) a Useful or Useless Number?

January 7, 2025

The concept of Body Mass Index (BMI) was developed by the Belgian scientist Adolphe Quetelet in the early to mid-19th century. The original goal was to determine the degree of obesity in a particular region or country. He didn’t intend for BMI measurement to be used in the medical community to assess the risks associated with obesity. It wasn’t until the 1960’s when a cardiologist named Ancel Keys began to notice that obesity contributed to negative health-related conditions, especially heart disease(1). Body weight in proportion to height was used as an indirect value about the build, obesity, or fatness. 

Why the BMI is Relevant

With this in mind, why is the BMI measurement relevant today? A large number of studies looking at longevity and risk of diseases such as high blood pressure, diabetes, and death have used BMI because it was easy to measure and provided a single consistent number. Some advocated using a fat caliper to measure percent body fat, but this was dependent on the person doing the measurements, which could give false results. If you look at the graph below, you will see that when the BMI is less than 18 and greater than 25, the risk of death increases markedly.  Looking at the graph below, don’t let the small numbers next to the mortality risk on the Y-axis fool you. As the BMI increases, the risk of dying increases. When compared to a person with a BMI of 25, the risk of death is around 180% greater at a BMI of 35 and around 225% greater when the BMI is greater than 40(2). 

If you take a look at the graph below, you will see that the percent of people developing diabetes or hypertension increased greatly as you moved from a healthy BMI of 25 towards an unhealthy BMI of greater than 40(3).  

Diabetes

Body Mass Index (BMI)

Hypertension

In conclusion, BMI is not a perfect measurement. There are certain people with a high BMI (>40) who happen to be professional athletes and have an increased weight. This represents a very small minority of people who have a BMI>40. Perhaps in the future, with affordable technology, we will be able to measure percent body fat in different parts of the body and incorporate this information into future studies so that we don’t have to rely on the imperfect BMI. Until then, we continue to use BMI to help evaluate our patients and to determine their risk of developing disease and who would benefit from different types of interventions depending on the weight and height.

References

  1. Henry Blackburn* and David Jacobs Jr†
    International Journal of Epidemiology, 2014, 665–669 doi: 10.1093/ije/dyu061
    Advance Access Publication Date: 1 April 2014   https://academic.oup.com/ije/article/43/3/665/2949550
  2. Indices of relative weight and obesity* :Ancel Keys, Flaminio Fidanza, Martti J Karvonen, Noburu Kimura, Henry L Taylor.  International Journal of Epidemiology, Volume 43, Issue 3, June 2014, Pages 655–665, https://doi.org/10.1093/ije/dyu058
  3. The relationship of body mass index to diabetes mellitus, hypertension and dyslipidaemia: comparison of data from two national surveys.  H E Bays, et al. Int J Clin Pract. 2007 May1; 61(5): 737-747 https://pubmed.ncbi.nlm.nih.gov/17493087/

Dr. Leon Katz MD, FACS, FASMBS, is a bariatrician specializing in non-surgical, medically supervised weight loss and currently practices at Dr. Leon Katz Medical Weight Loss Center.

Body Mass Index (BMI)
Leon Katz

ABOUT THE AUTHOR

Dr. Leon Katz MD, FACS, FASMBS, is a bariatrician specializing in non-surgical, medically supervised weight loss. He focuses on patients seeking alternatives to surgery and those needing care after bariatric procedures. Dr. Katz was recently the director of a major medical weight loss program. With extensive experience in establishing successful weight management programs, he now concentrates exclusively on non-surgical weight loss solutions. Dr. Katz is a Diplomate of the American Board of Obesity Medicine and Fellow of American College of Surgeons. Dr. Katz currently practices at Dr. Leon Katz Medical Weight Loss Center.