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Rethinking Body Mass Index: Why I Don't Use BMI

Written By: Frances Spence

Reviewed By: Heather Bray, RD


*Disclaimer: the views and opinions of this article are based on the best available evidence and my professional opinion as a Registered Dietitian. This article is not meant to act as a substitute for medical or medical nutrition advice. For medical or medical nutrition advice that is designed for your individual needs, please consult your doctor or Registered Dietitian. 


Hello, health enthusiasts!


Let's talk about a metric that's been a staple in health assessments for years: Body Mass Index, or BMI. While BMI might seem like a straightforward way to measure health, it's a lot more complicated—and less helpful—than you might think.


What is BMI?


BMI is a simple calculation using height and weight to place individuals into categories like underweight, normal weight, overweight, and obese class 1, 2, and 3.


Originally devised in the early 19th century by Lambert Adolphe Jacques Quetelet, a Belgian astronomer and statistician, BMI was never intended as a measurement of health but designed as a population census tool​​. Quetelet was not a physician but was interested in applying mathematical principles to the social sciences. In the 1830s, during his sociological research, he developed what he called the "Quetelet Index" to describe the average European man in terms of the distribution of various physical dimensions for the purpose of distributing resources. His formula, weight divided by height squared (kg/m²), was used in the study of determining the “ideal body weight” of the general population. The inconsistent and unreliable results from tests shockingly led to the conclusion that the simple math equation should set the standard. [1]


BMI became widely adopted as a health metric in the mid-20th century despite its origins as a tool for population studies. Initially, it provided a quick, easy way to categorize people's weight relative to their height. However, it didn't consider individual body composition differences, such as muscle mass, bone density, and overall body fat distribution​​. [2]


BMI in Today's World


Today, Body Mass Index (BMI) continues to be a prominent metric used across various domains—from healthcare to insurance, the fitness industry and even in research. Its widespread use is underpinned by its simplicity and cost-effectiveness; however, the reliance on BMI as a primary health indicator is increasingly contested due to its inherent limitations and implications.


person's hand using a calculator on a desk surrounded by papers dietitian ontario canada explains why she doesnt use BMI body mass index in practice



Broad Applications and Implications


Healthcare and insurance sectors utilize Body Mass Index (BMI) for different purposes, highlighting the tool's widespread but problematic use. In medical settings, BMI is primarily used to screen for potential health issues related to weight, such as identifying risks for diseases like type 2 diabetes and heart disease associated with being overweight or obese.


However, BMI's inability to differentiate between muscle and fat mass can lead to inaccuracies [4]. For example, athletes with high muscle mass might be wrongly classified as obese. Similarly, some insurance companies use BMI to determine policy pricing, categorizing individuals with high BMI as higher risk, often resulting in higher premiums. This practice, driven by financial motives, may not reflect individual health risks fairly, particularly for those with misleading BMI classifications due to their body composition.


Criticisms and Challenges


Accuracy and Relevance:

A significant criticism of BMI is its inability to accurately account for various physical and demographic factors such as muscle mass, bone density, biological sex, race and ethnicity. Studies have shown that BMI thresholds often do not align well with markers of health in certain racial and ethnic groups, potentially leading to underdiagnosis or overdiagnosis of health risks.


Health Implications:

Relying solely on BMI can lead to misdirected health advice. For example, individuals with a "normal" BMI might be overlooked for screening of metabolic abnormalities if they have unhealthy levels of body fat not reflected in their BMI. Conversely, healthy individuals with a high BMI might be subject to unnecessary interventions, bias or stigma.


Psychological Impact:

The use of BMI as a health standard can also have psychological effects, contributing to body image issues, eating disorders and may cause individuals to avoid seeking health care. The focus on weight rather than health can perpetuate a negative self-image and unhealthy behavior changes.


Why I Don't Use BMI

“BMI is deficient in at least three ways… does not measure body fat distribution… not a very good measure of body fat… BMI does not provide any insights into the heterogeneity of obesity or its genetic, metabolic, physiological or psychological origins.”[5]

  1. Not Originally intended for Health Assessments: Quetelet designed the BMI for sociological research, not to assess individual health or prescribe treatment​​.

  2. Lacks Nuance: BMI ignores several critical factors, such as sex, age, race, muscle mass, genetics, socioeconomic status, blood work/clinical metrics or medical conditions, relationship with food, and mental health. Due to their body composition, it can miscategorize fit individuals as overweight and unhealthy individuals as healthy​​.

  3. Perpetuates Weight Stigma: Focusing solely on weight and BMI can reinforce weight stigma in healthcare, discouraging people from seeking help and potentially leading to worse health outcomes​​.

  4. A Flawed Health Measure: Many health professionals, including myself, now recognize that BMI is not only simplistic but also potentially harmful for assessing individual health​​


Image with a scale, calculator and measuring tape with text that says you are more than a math equation to explain why Body Mass Index BMI is flawed Registered Dietitian in Ontario Canada
Image by Frances Spence


Better Ways to Measure Health


So, how should we measure health? Here are a few holistic indicators:


  • Energy levels: Feeling energetic and alert throughout the day without heavy reliance on caffeine can be a good indicator of health.

  • Are you able to make it through the day without an "afternoon crash?"

  • Are you able to focus better at school/work? 


  • Digestive Health: Regular bowel movements and minimal digestive discomfort (e.g. bloating) are big wins that should count as success metrics in your health journey if this is something that you’ve previously struggled with.


  • Physical Fitness: Improvements in strength, endurance, and flexibility are signs of good health. Establishing a balanced diet and regular exercise routine can help improve aches, pains and stamina


  • Mental Wellbeing: A positive self-image and stable mental health can significantly affect overall health. A balanced diet and regular exercise, when approached with a healthy, self care mindset, can improve these thought and feelings


  • Improvements in blood work: Nutrition and exercise can play a big role in the following blood markers: blood sugar, cholesterol panel (HDL, LDL, and triglycerides), inflammatory markers (hsCRP), and iron levels


Bottom Line

While BMI can give a rough estimate of a population's weight status, it's not appropriate for individual health assessment. Let's shift our focus from weight to wellbeing and from stigma to support. We can't change the system overnight, but we can start by having informed conversations with our healthcare providers about truly holistic health assessments.


Here are a couple resources I’d recommend that go beyond the numbers of it all:


Remember, your health journey is unique, and you deserve a measurement system that respects and reflects that uniqueness.


Stay healthy and informed!




References 

  1. Barrette L. URMC Newsroom [Internet]. Is BMI Accurate? New Evidence Says No; 2024 Jan 8 [cited 2024 May 14]. Available from: https://www.urmc.rochester.edu/news/publications/health-matters/is-bmi-accurate#:~:text=Developed%20by%20a%2019th%20century,population%20census%20in%20the%20Netherlands.

  2. Eknoyan G. A History of Obesity, or How What Was Good Became Ugly and Then Bad. Adv Chronic Kidney Dis [Internet]. 2006 Oct [cited 2024 May 10];13(4):421-7. Available from: doi.org/10.1053/j.ackd.2006.07.002

  3. Holy Healthy UMC, steps to faith-based health and wellness [Internet]. About the Body Mass Index (BMI); [cited 2024 May 10]. Available from: http://www.holyhealthyumc.com/forms/BMIWaistCalories.pdf

  4. Is it Time to Consider Body Mass Index to be Bad Medical Information (BMI)? J Obes Nutr Disord [Internet]. 2021 [cited 2024 May 10]. Available from: doi.org/10.29011/2577-2244.100045 

  5. Bray GA. Beyond BMI. Nutrients [Internet]. 2023 May 10 [cited 2024 May 10];15(10):2254. Available from: https://doi.org/10.3390/nu15102254

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