Is The Body Mass Index (BMI) A Good Indicator Of Being Overweight?
Body Mass Index is a method used by many GPs to determine whether a patient is overweight.
The trouble with this method of evaluation is that according to many health professionals it is very dated and out of touch with the variety of modern forms of body composition tests readily available.
To calculate your BMI, use the following formula:
Your weight (kg)
_______________________
Your height x your height.
So, if we take me as an example:
85kg
________
1.83 x 1.83m
Therefore, my BMI = 25.3. If I stood in front of a doctor with a BMI of 25.3, he /she would look at a chart and declare me either:
-
Underweight: Less than 18.5
-
Healthy weight: 19.0-24.9
-
Overweight: 25.0-29.9
-
Obese: Over 30.
So, according to the BMI, despite the fact that I am a personal trainer, exercise 4-5 days a week and follow a healthy diet, the doctor could potentially interpret this reading as a sign that I'm getting a little porky and should think about shedding a few pounds.
Although a BMI reading will give a GP a rough idea of how overweight a patient is, true obesity levels should not be determined by what the scales say, but by how much excess body fat you carry. Bathroom scales measure our weight as a whole, from the lunch we have just eaten (or passed), the water in our cells, our fat stores and our muscle mass. Fluid retention alone can easily add a further 2-3kg, potentially pushing someone from the healthy category to overweight status.
As a regular exerciser and someone who enjoys all forms of exercise, from running to rowing to weight training, I am lucky to have a low level of body fat (less than 12%) and a fairly bulky musculature, but according to the BMI system I am verging on unhealthy. I have lost count of the number of clients over the years who have been told their BMI is too high, yet when I have taken a body-fat reading, they are well within normal limits.
That said, despite its shortfalls, many GPs would argue that it is a quick and easy way to inform some people they are overweight and need to re-adjust their lifestyle. Time is not a GP's friend, so the BMI provides a practical guide as to what weight most people should be, but it is far from perfect. Due to a lower muscle mass, the BMI is slightly more accurate for women than men but unless you know you are excessively overweight, if I were you, I'd take my BMI reading with a pinch of salt and I'd advise you to get your body fat measured as well.