What does your BMI really say about your health?

22-04-2022 Cecily Ellis

Do you know your BMI? It is a widely known and used metric, and many people are very aware of where they fall on the BMI graph. But what does it really say about your health? Let’s take a deep dive into what the most recent studies have to tell us on the topic.

First things first; BMI or Body Mass Index is a metric used to categorize people into a number of categories. It expresses the relationship between your height and weight [1], and allows you to compare this number to the categories provided. The number and ranging of the categories varies, but generally those with a BMI below 18.5 are classed as underweight, those between 18.5 and 25 are considered to have a normal weight, those between 25 and 30 are viewed as overweight, and those with a BMI higher than 30 are classified as obese.

Over the years these numbers have been adjusted and expanded upon, so that they now differ depending on heritage, age and gender [2]. You can calculate your BMI on one of the many websites available, or follow this simple formula.

BMI = (weight in KG) / ((Height in meters)^2)

This is all very straight forward, and due to the convenience and clarity of BMI it is often used to give people an estimation of their health. The main criticism however is that BMI does not take body composition into account. You can have a BMI of 29 and be a couch potato who has never exercised a day in your life. Or you can have a BMI of 29 and be a competitive bodybuilder with an extremely low fat percentage (and likely a high amount of doping in your bloodstream, but that’s another story). This has led many to discuss the value of this metric, considering fat percentage to be the main factor contributing to disease instead of just BMI [1]. A valid point, though one could argue that if you are the exception like the bodybuilder described above you’d probably know it.

There is also another element you should take into account when deciding how much weight to give to your BMI (pun intended). Many people confuse the distinction between a statistically significant correlation seen in a large group, and what this says about them personally. We know that people who fall into the overweight or obese BMI category experience higher rate of morbidity and mortality [2, 3]. We also know that there are obese people who seem completely healthy [4], and people who fall into the normal weight category who are metabolically ill [5]. So yes, a higher BMI does mean you have a higher chance of getting ill, but among other things, it doesn’ttake into account other factors that also play a big part, and therefore cannot be directly translated to your personal health status. You need to study large groups of people to see the bigger picture, but you also need one-on-one tests to determine the best course of action for each person involved.

On the whole, BMI is neither the ‘amazingly important health tool’ nor the ‘completely meaningless bullshit term’ it’s often made out to be. It can be very useful when properly used and understood. Especially when combined with other factors such as waist circumference or blood pressure and applied to large groups. Generally I would advise not stressing about your BMI, but looking at the bigger picture. It can be an indicator of risk, but should definitely not be keeping you up at night. Once again coach Jeremy’s favourite answer to everything applies. What does BMI really say about your health? It depends.

Refefrences

[1] Lee, Dong Hoon, and Edward L. Giovannucci. “Body Composition and Mortality in the General Population: A Review of Epidemiologic Studies.” Experimental Biology and Medicine, vol. 243, no. 17–18, Dec. 2018, pp. 1275–1285, doi:10.1177/1535370218818161.
[2] Abdelaal, Mahmoud et al. “Morbidity and mortality associated with obesity.” Annals of translational medicine vol. 5,7 (2017): 161. doi:10.21037/atm.2017.03.107
[3] Samaras, Thomas T et al. “Longevity, mortality and body weight.” Ageing research reviews vol. 1,4 (2002): 673-91. doi:10.1016/s1568-1637(02)00029-6
[4] Stefan N, Kantartzis K, Machann J, et al. Identification and characterization of metabolically benign obesity in humans. Arch Intern Med. 2008; 168( 15): 1609–1616.
[5] Ruderman NB, Schneider SH, Berchtold P. The “metabolically-obese,” normal-weight individual. Am J Clin Nutr. 1981; 34( 8): 1617–1621.

Cecily Ellis

About Cecily Ellis

Cecily is a CrossFit, Strength and Olympic weightlifting coach at UnScared. She devoted most of her young life to competitive swimming and gymnastics, only to discover UnScared and fall in love with CrossFit and Olympic Weightlifting. She now spends her days studying computer science, doing snatches and baking protein-filled goods. Don’t let her love of fluffy animals and British accent deceive you however, her puns are still unBEARable.

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