The Body Mass Index (BMI) is used by many GPs to determine whether a patient is overweight. The trouble with this method, according to many health professionals, is that it is very dated and out of touch with the variety of readily available and modern forms of body-composition tests.
Your BMI is your weight (in kilograms) divided by your height (in metres) squared. Less than 18.5 is considered underweight; a healthy weight is 19.0 to 24.9; 25.0 to 29.9 is overweight; and over 30 is obese. So, to take me as an example, 85kg is divided by 1.83 x 1.83 metres. This gives a BMI of 25.3. So, according to the BMI, in spite of the fact that I am a personal trainer, exercise four or five days a week and follow a healthy diet, a doctor could interpret this reading as a sign that I’m getting a little porky and should think about shedding a few pounds.
Many GPs would argue that it is a quick and easy way to inform some people that they are overweight and need to adjust their lifestyle. But it is far from perfect. Due to the lower muscle mass of women, BMI is slightly more accurate for them than for men but, unless you know that you’re excessively overweight, you should take your BMI reading with a pinch of salt and get your body fat measured as well.