Body Mass Index, more commonly known as BMI, is an equation used to determine whether a person is overweight, obese or not. This is the standard formula used by the majority of healthcare professionals around the world as it is easily measureable and presents clear boundaries to establish where on the weight scale the patient lies.
In order to calculate your BMI you need to divide your weight in kilograms by hour height in metres squared. Once you have your result all you need to do is check it against a classification chart to see where on the weight scale you sit.
Unfortunately, BMI is not as accurate a measure of a person’s weight as many would have you believe, despite its prolific use around the world by doctors, nurses and statisticians.
The Belgian mathematician, Lambert Adolphe Jacques Quetelet, devised the BMI formula between 1830 and 1850. Since then, BMI has come to be relied upon by many people, including physicians, because of its apparent numerical authority for medical diagnosis. However, this was never the BMI's purpose; it was meant as a simple means of classifying physically inactive individuals, or populations, with an average body composition. Therefore, whilst it is easy to use as a general calculation, BMI is limited in its accuracy.
To begin with, there is no logical reason to square a person’s height (unless you’re trying to create a formula to fit a specific set of data Monsieur Quetelet!). Add to this the fact that the measurements completely ignore a person’s waist size (the clearest, visual, indicator of obesity) and you have an inherently flawed method.
Furthermore, BMI makes no allowance for the proportions of bone and muscle within the body. Bone is denser than muscle and twice the density of fat, therefore, heavier. Muscle, as everyone knows, is also heavier than fat, thus, people with larger muscles, strong bones and little fat will present a high, and inaccurate, BMI. This is perhaps the second most important oversight in the calculation, after waist size.
In essence, BMI is marginally acceptable if you are looking for some very general indicators of obesity, but it is a formula that doesn’t hold up against scientific measurements; particularly when healthy individuals with muscular definition can be classified as overweight and obese. Waist circumference is an infinitely more accurate indicator of obesity, and it is agreed that a waist circumference greater than 80cm (32in) for women and 94cm (37in) for men increases the risk of cardiovascular diseases, with the greatest risk for women being a waist measurement of more than 88cm (35in) and men, a waist measurement of more than 102cm (40in). If you would like to calculate your waist circumference wrap a measuring tape midway between your hip bone and rib cage as you exhale.
Alternatively, the waist-hip ratio is an even more accurate indicator of the proportion of fat stored in your body. By measuring your waist as above and your hips at their widest point, you can divide your waist measurement by your hip measurement to ascertain your waist hip ratio. For men, a ratio above 1.0, and for women, a ratio above 0.8, indicates that you are at a greater risk of health problems.
There may still be hope for some of the 60% of Gibraltarians classed as overweight or obese. However, no amount of measurements, formulas and data analysis can replace good old fashioned regular exercise and healthy eating which has the added benefit of boosting your metabolism and helping you to burn more calories with greater ease!