Image by Charlotte O’Daly
1. What is BMI?
BMI stands for Body Mass Index, it is calculated by measuring your height and weight, then dividing your weight by height squared. If this sounds a bit beyond your mathematic means, or if you are still not sure its right the NHS website has a BMI calculating tool. You just enter your age, sex, height and weight and then the tool will not only tell you your BMI number but whether your BMI means you are healthy, overweight or obese.
2. What is a healthy BMI?
A healthy BMI for adults is between 18.5 and 24.9. A BMI of 25 or above means that you’re overweight. A BMI of over 30 puts you into the obese category. 40 or above is morbidly obese, whilst a BMI of 18.5 or lower means your underweight.
3. BMI can be misleading
BMI does not differentiate between body fat and body muscle, and as muscle weighs more than fat your weight and height might give you an overweight BMI but your body fat percentage could be low. For example Arnold Schwarzenegger’s BMI falls into the obese category according to Health.com but you would not think he was porky. Equally Tom Cruise’s BMI makes him overweight, but he still manages to fulfill all those physical impossible missions.
4. Where does BMI come from?
BMI is not a new thing. In fact it was devised somewhere in 1832 by the Belgian mathematician and statistician Adolphe Quetelet. It was initially known as the Quetelet Index. However it become popular after the 1970’s when a paper in the Journal of Chronic Disease by scientist and dietitian Ancel Keys coined the term BMI. Keys said BMI was the best means of measuring body fat. However he did caution it was not appropriate for individual diagnosis but better as a tool for population analysis.
5. Should you go on BMI alone?
Well no. It was never meant for individual diagnosis. It was originally created out of studies based on men in the 19th Century, therefore it is not ideal for women, athletes, or the frail. Many doctors carry out other measurements to help them determine your weight health. A waist circumference task for example measures abdominal obesity which is a good way of measuring your risk of weight associated illness like heart disease or type 2 diabetes.