The term Body Mass Index (BMI for short) has been used as a measure of body weight status for decades. But it does attract some criticism that it’s not a fair assessment for some people, so why is it still the go-to measurement today? Join me in this blog as we explore the pros and cons of BMI. Plus, we look at whether there are any alternative methods to gain insight into weight status and an individual’s potential weight-related health risks.
BMI is a measure used to assess the weight status of a person in relation to their height. This is done by calculating an individual's weight in kilograms by the square of their height in meters (BMI = weight (kg) / height (m)^2). Whilst the calculations may sound complex, BMI simply assesses whether you are the correct weight for your height. The measure’s primary purpose is to provide a quick and easy way to place individuals into weight categories, such as underweight, normal weight, overweight, and obese.
BMI is used across the world for the following purposes:
While BMI is a convenient and adequate tool for many, it may not accurately assess individuals with higher muscle mass, such as bodybuilders and athletes. This is because muscle is denser than fat, meaning it weighs more per volume but takes up less space. So, if you’re really into the gym and your BMI figure categorises you as 'overweight,' it could be due to your muscular physique rather than excess fat. And having more muscle mass can be incredibly beneficial for overall health and fitness, even if it bumps up your BMI!
Additionally, BMI may not accurately reflect health risks in older adults or individuals from different ethnic backgrounds who can have varied body compositions even at the same BMI level. This diversity highlights the challenge of using a universal BMI scale across all populations. But that said, research still supports BMI as a reliable starting point for the majority of individuals looking to lose, gain or maintain weight.
In addition to BMI, there are also a variety of measurement methods to not only determine how much fat we have but also where we store fat in our body (something BMI can’t do!) It is important to consider these alongside BMI, to ensure that we are using the most appropriate and helpful method to assess people.
Other ways to measure weight-related health status include:
In the absence of anything better, for now BMI remains a valuable tool to assess the weight status and potential health risks of an individual in a user-friendly way.
However as this blog has hopefully explained, it can only ever be an estimation of whether an individual actually IS overweight, and whether that could have an impact on their health. It’s important to recognise there are exceptions - such as groups who are extremely athletic with a high muscle mass, like rugby players or bodybuilders - where BMI is not the best assessment and other measurements should be taken to prevent misdiagnosis of weight category and fat-related health risks.
In general, supplementing BMI with other measures such as waist-to-height ratio or skin fold tests, plus advice from a healthcare professional is the best approach for a more rounded picture of an individual’s weight-related health risks. But as a useful starting point and monitoring tool for weight loss progress, BMI continues to provide a useful and practical measure for most people.
Nutritionist Beth Furness (ANutr), holding a BSc in Nutrition and Health, is deeply dedicated to applying evidence-based knowledge to all aspects of nutrition. Her passion lies in fostering healthy relationships with food, ensuring that everyone maintains a balanced and sustainable approach to nutrition.
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