For decades, Body Mass Index (BMI) has been the standard measure for assessing health based on weight and height. While it’s still widely used in healthcare, fitness, and even insurance, experts are increasingly criticising BMI for being outdated and inaccurate. Its reliance on a basic calculation oversimplifies health and overlooks critical factors that affect well-being.
What Is BMI?
BMI is calculated by dividing a person’s weight (in kilograms) by their height (in metres) squared. It categorises individuals into weight ranges such as underweight, normal weight, overweight, or obese (Nuttall, 2015). While easy to use, BMI has serious limitations when it comes to assessing true health risks. Below is an image of 5 women with the same BMI of 30, which already shows how they are all of different body shapes.
Why BMI Is Inaccurate
BMI Ignores Fat Distribution: BMI only considers total body weight, not where fat is stored. However, fat stored around the abdomen (visceral fat) poses a much higher risk for conditions like heart disease, diabetes, and stroke compared to fat stored elsewhere. Two people with the same BMI could have drastically different health risks depending on where their fat is distributed (Taefit et al., 2019).
BMI Doesn’t Differentiate Between Fat and Muscle: BMI doesn’t distinguish between fat and muscle mass. This means that a fit, muscular person could be classified as overweight or even obese, despite having a low body fat percentage. Conversely, someone with high body fat but little muscle could fall into the “healthy” BMI range (National Academies of Sciences, Engineering and Medicines, 2010).
BMI Overlooks Body Composition: BMI gives no insight into muscle, bone density, or water retention—factors that significantly influence health. For example, older adults tend to lose muscle mass but may still have a “normal” BMI, masking potential health issues (Michels, Greenland and Rosner, 1998).
BMI Fails to Consider Age, Sex, and Ethnicity: BMI applies the same formula to everyone, ignoring how age, sex, and ethnicity impact body composition and health risks. Research shows that some ethnic groups are more prone to conditions like Type 2 diabetes at lower BMI levels, while others may carry extra weight with fewer health complications (Dulloo et al., 2010).
BMI Provides No Insight Into Metabolic Health: BMI doesn’t measure important indicators of health like cholesterol, blood pressure, or insulin sensitivity. A person with a "healthy" BMI might still be at high risk for chronic illnesses due to poor metabolic health (Lang et al., 2015).
Why Is BMI Still Used?
Despite its flaws, BMI remains popular mainly because it’s simple, quick, and cost-effective. It’s commonly used in large-scale health surveys and population studies where precise body composition measurements aren’t practical. However, relying on BMI for individual health assessments often leads to misleading results.
What’s the Alternative?
As BMI’s limitations become more apparent, better alternatives are gaining traction:
Body Fat Percentage: Directly measures how much of the body is fat versus lean mass.
Waist-to-Hip Ratio: Evaluates abdominal fat, a key indicator of health risk.
Advanced Health Metrics: Tools like BVI incorporate multiple data points, including fat volume, body shape, and demographics, to create personalised health profiles.
Body Volume Index (BVI): Measures fat distribution using 3D imaging for a more accurate assessment.
The Future of Health Assessments
It’s time to move beyond outdated measures like BMI and adopt more accurate, personalised tools. Health isn’t just about weight - it’s about body composition, fat distribution, and how these factors influence long-term well-being.
Reference List
Dulloo, A., Jacquet, J., Solinas, G., Montani, J., & Schutz, Y. (2010). Body composition phenotypes in pathways to obesity and the metabolic syndrome. International Journal of Obesity, 34(Suppl 2), S4-S17.
Lang, P., Trivalle, C., Vogel, T., Proust, J., & Papazian, J. (2015). Markers of metabolic and cardiovascular health in adults: Comparative analysis of DEXA-based body composition components and BMI categories. Journal of Cardiology, 65(1), 42-49.
Nuttall, F. Q. (2015). Body mass index: obesity, BMI, and health: a critical review. Nutrition today, 50(3), 117-128.
Michels, K., Greenland, S., & Rosner, B. A. (1998). Does body mass index adequately capture the relation of body composition and body size to health outcomes? American Journal of Epidemiology, 147(2), 167-172.
National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Food and Nutrition Board; Roundtable on Obesity Solutions; Callahan EA, editor. Translating Knowledge of Foundational Drivers of Obesity into Practice: Proceedings of a Workshop Series. Washington (DC): National Academies Press (US); 2023 Jul 31. 10, The Science, Strengths, and Limitations of Body Mass Index. Available from: https://www.ncbi.nlm.nih.gov/books/NBK594362/
Tafeit, E., Cvirn, G., Lamprecht, M., Hohensinn, M., Moeller, R., Hamlin, M., & Horejsi, R. (2019). Using body mass index ignores the intensive training of elite special force personnel. Experimental biology and medicine (Maywood, N.J.), 244(11), 873–879.
Comments