BMI... Is it a useful tool for health status?

Body Mass Index, or BMI, is a measure used to approximate the amount of body fat you have. This measure can help to predict your health status, risk for developing chronic disease, as well as lifespan.

To workout your BMI, you will need to know your height in metres and your weight in kilograms.

Calculating your BMI

BMI = weight (kg) / height (m)2

For example, for a person who weighs 75kg and is 1.8m high:

BMI = 75 / (1.8 x 1.8)

BMI = 23.1

What does your BMI mean?

BMI Classification

< 18.5 Underweight

18.5 – 24.9 Healthy weight range

25 – 29.9 Overweight

> 30 Obese

If your BMI is greater than 25, you are considered to be Overweight, and if it’s over 30, you’re classified as Obese.... But what does this mean?

BMI is an approximate measure of your total body fat and although your waist circumference is a better predictor for health risks at an individual level, BMI provides good health guidance at a population level.

In general, an increase in BMI is caused by an increase in body fat, which in turn increases the risk for poor health and certain conditions. For example, being overweight increases your risk for Cardiovascular disease, Osteoarthritis and Type 2 Diabetes, and being Obese increases the risk for these conditions even more.

Exceptions to the BMI rule

If you contain a lot of muscle mass, are very tall or very short, have particular disabilities, or are from certain ethnic groups, then the BMI tool for estimating fat mass is not super accurate. Which means its classification system (e.g. underweight, healthy, overweight) will not be suitable for people from these groups.

For example, a lot of body builders are classified as overweight, however body builders have very little body fat. Hence the BMI tool for this group is not valid.

BMI... a very useful tool

Despite the few mentioned exceptions, BMI is a very useful tool for predicting health status, as well as health risks. Majority of people in the overweight BMI range are at increased risk, or suffer from, more health problems than those in the healthy BMI range. This risk is even more so significant for those who are Obese.

Although BMI is a useful tool…

I have always believed that your health behaviors are more important than your BMI range. If you eat well (mostly plant-based wholefoods), exercise daily, get good quality sleep, manage your stress and get some sun each day, these behaviours are working strongly in your health's favour.