This special issue takes a closer look at BMI
What is BMI?
Body mass index (or BMI for short) is a rough indicator of health. It is based on how much “weight” you carry for your size and is often used to indicate the risk of developing certain diseases. It cannot, however, tell you how “fat” you are, as it does not distinguish between the weight of muscle, bones and fat.
How is it measured?
BMI is calculated using your weight (in kilograms) and height (in metres squared). The calculation is written as BMI = kg/m2. For example, if you are 70kg (about 154 lbs) and 1.8m tall (about 5’ 11”), your BMI will be 21.6 [i.e. 70/(1.8×1.8)].
What should mine be?
For many people, a healthy BMI is in the range of 20.0 to 24.9. Less than 20.0 is regarded as “underweight”. In contrast, 25.0 to 29.9 is regarded as “overweight” and 30.0+ is regarded as “obese”. It is important to note, however, that these hard boundaries are often disputed (e.g. some people use 18.5 to 24.9 as the healthy category) and may differ based on age, gender and race.
How can I improve it?
Unless you plan to grow significantly in height, the only way to change your BMI is to change your weight. Losing weight will reduce your BMI and gaining weight will increase your BMI.
What else should I know?
Many people disagree with using BMI as an index of health, claiming that the boundaries of “healthy” and “overweight” are somewhat arbitrary. For example, here is an article with 10 valid reasons why BMI could be considered as “bogus”. On the flip side, in a combined study of more than 120,000 disease-free people, those who were in the “overweight” and “obese” categories were 3.3 and 9.4 times more likely to develop diabetes over the 10 years studied than those in the “healthy” category, regardless of sociodemographic factors (age, wealth, gender etc) and lifestyle. Since a number of studies have shown this, BMI is likely to have some validity. A high BMI might even increase the risk of severe COVID-19 complications and death, however there are some really complex explanations for why this might not be clear-cut.
What is my personal experience?
I am fortunate to have a rapid metabolism, a borderline obsessive passion for sport and fitness and a healthy relationship with food. I have always been within the “healthy” BMI window and I will do everything needed to keep it that way.
Acknowledgements
This special issue has been put together from a variety of sources and personal experience. To learn more, check out these previous articles featuring BMI, or visit the NHS or AHA websites for a great introduction.
Abstract Athlete 