A recent study of patient data from Melbourne’s eastern suburbs published in the Medical Journal of Australia (MJA) showed GPs are not checking their patients’ Body Mass Index (BMI) or measuring their waist circumference. The article’s authors interpret this as a shortcoming but these doctors may actually be avoiding the trap of thinking simplistic measurements help patient health and well-being.
The paper’s authors assume – as does the National Health and Medical Research Council – that if GPs weighed and measured their patients, they'd be better able to address weight-related health problems.
But there are good reasons to be sceptical about whether scales are an effective weapon in the so-called “war on obesity”. In fact, weighing people may do more harm than good by giving an unreliable picture of the complex realities of health and weight.
Poor Indicators
Take, for example, Body Mass Index (BMI), which is calculated by dividing weight (in kilograms) by the square of height (in metres). BMI was originally devised to determine the “average” person in a given population. While a population is obviously made up of individuals, the two are clearly not the same thing and BMI is a blunt instrument when it comes to the latter.
Consider this 2008 article in Internal Medicine that found just over a half (51.3%) of people in the overweight range (BMI of between 25 and 30) and almost a third (31.7%) of those considered obese (BMI of between 30 and 35) are metabolically healthy. That means they don’t have raised blood sugar levels, raised cholesterol, or high blood pressure, all of which pose a risk to good health. The study authors also found nearly a quarter (23.5%) of people in the so-called “healthy” range, that is, with a BMI between 20 and 25, may have these risks to their health.
Waist circumference is similarly inaccurate. Pulling a measuring tape around someone’s waist simply won’t tell you if they’re healthy or unhealthy because health is far more complex than a certain number of centimetres.
In fact, one number — be it BMI, waist circumference or whatever comes next — will never tell you about any one individual’s health and well-being. If we’re looking across a population, then we may see some associations between increased BMI and an increased risk of diabetes, for instance, but that’s completely different to assessing any one person visiting a doctor.
