BMI

How do us well-educated medical types inform the lay public on what is a healthy weight? So far the model of choice for the Australian Government is BMI (body mass index) for weight, or perhaps preferably waist circumference.

 

As I’ve alluded to earlier, obesity is a complex issue and the morphological variation in the human population is quite astounding. Given this information, it doesn’t take a 1^st-year medical student to figure out that BMI is severely limited in usefulness. As the government health website says, “There are no perfect measures of overweight and obesity. (BMI) is used most often – particularly in assessing overweight and obesity at the population level. At the individual level however, BMI does have some limitations in that it can be influenced by age, gender and ethnicity. Also, BMI does not distinguish fat mass from lean mass, nor does it necessarily reflect body-fat distribution.”

BMI is rather useful for looking at population-level data, but for an individual it is pretty close to useless. I knew a hulking young recreational bodybuilder who was upset when he learned he was ‘overweight’ according to the BMI (it was pretty funny). I would hazard a pretty confident guess that every single current holder of an NRL contract is also ‘overweight’ according to the BMI formula. Likewise, I’m sure there are plenty of people around with a ‘spare tyre’ and not much muscle mass who think they are completely in the clear based on getting their BMI down to 24.8 through crash dieting. Accordingly, a preferred measurement of overweight and obesity is waist circumference, with 88cm for women and 92cm for men set as the cutoffs. Again, simply having a raw number as a national health guideline has obvious severe limitations.

 

At the moment you’re probably sitting there thinking “Yeah righto mate if you’re so smart why don’t you make yourself useful and come up with some better healthy weight guidelines that are actual indications of health?” Good question reader, and the answer is this: I won’t make any better guidelines because I can’t think of anything better. Neither can anyone else, and for communicating health information to the masses, this is about as good as it’s gonna get unfortunately. Probably the best advice I can give anyone about a healthy weight is to have a good long hard look in the mirror, and decide whether you are in healthy shape. Every individual knows their inherent body type and the quirks of their own metabolism, so they should be in pole position to make a judgement about whether they need to gain or lose weight. But here’s the rub; unfortunately psychology and self-esteem play a large part in this aspect of health so it is difficult if not impossible for individuals to make objective judgements about whether their body morphology is within a healthy range. Also, body weight and ‘health’ lie on a continuum without discrete ‘healthy’ and ‘unhealthy’ points, so Average Joan is on a hiding to nothing to decide whether she really needs to lose weight. So it’s back to the drawing board and we are left with broad, essentially meaningless guidelines like BMI.