Why I hate BMI as an indicator of the severity of an eating disorder - or even that an eating disorder exists in the first place

In my PTSD sessions we are going round and round in (necessary) circles as my head tries to process the issues I was having with CAMHS during the first 7 or 8 months of my son's eating disorder treatment. One of the main pictures I keep getting in my mind is of the CAMHS nurse twiddling her cardboard BMI (Body Mass Index) indicator wheel every week. For CAMHS, as with many medical professionals, BMI is still trusted as an indicator of healthy weight, despite the fact that - at a so-called 'healthy BMI' - an eating disorder can be raging.


BMI was devised in the 1830s by Lambert Adolphe Jacques Quetelet (1796-1874), a Belgian astronomer, mathematician, statistician and sociologist, (NOTE: No reference to being a medical professional!!) as a measure of obesity. It was subsequently adopted by health professionals on both sides of the Atlantic as the default formula for deciding whether or not a person is a healthy weight.

That's quite a long time ago. 

And it was devised as a measure of obesity.

It's high time that this out-dated and flawed formula was revised to take into account the vastly varying biological makeup of human beings, not to mention genetics, and the difference between fat, muscle and bone – none of which the BMI scale takes into account.

As Medical News Today points out: "BMI ... does not measure your overall fat or lean tissue (muscle) content. ... The measurement is flawed, especially if the person carries a lot of muscle ... Short people being told they are thinner than they really are, while tall people are made to think that they are fatter than they are."

And so many people in the eating disorder community have been affected by this insistence of STILL using a formula that's nearly 200 years old!

It can be SO VERY damaging when an eating disorder patient is told that their BMI is "within the healthy range" or that it's "just slipped into the healthy range" or "healthy".

In the case of my son, this information was conveyed with added "Congratulations!" and big smiles. As if he'd suddenly recovered.

Of course to him, the message was that he didn't need to continue to put on weight. He'd reached 'weight restoration'. Worse, that he was 'fat'.

As a result he immediately cut back on his food intake and lost weight.

Not surprising, huh...

When my son fell sick with anorexia in 2009, aged 15, his BMI was pretty high; remember he was a 'prop' in the school rugby team.

It was probably mainly muscle (i.e. he didn't even remotely 'look fat'), but undoubtedly it would have put his BMI pretty high up on the BMI scale (because BMI doesn't distinguish between fat, muscle or bone).

Indeed I'm fairly sure that many fit and healthy rugby players and other athletes would be considered as 'obese' if you applied the rigid BMI scale to them.

So even though Ben had probably lost around a quarter of his body weight, increasing to close to a third as his weight dropped to its lowest level halfway through the eating disorder treatment, he was still hovering around or just below the 'healthy' level for a BMI.

And yet, as you will know from reading this blog, his anorexia was raging. The list of eating disorder symptoms he was exhibiting was as long as your arm.

Longer, probably.

This is why I - and many others in the eating disorders community - believe that there should be less (or even no) emphasis on BMI is an indicator of seriousness of an eating disorder and of recovery. And also the reliance on BMI for diagnosis, because boys like Ben may never even reach the low BMI required to diagnose their eating disorder as anorexia nervosa - or for in-patient treatment.

And, of course, BMIs can be completely irrelevant when it comes to diagnosing or judging the severity of deadly eating disorders such as Bulimia.

Going back to the EMDR sessions (currently being used to treat my PTSD)... That confounded BMI wheel appears in flashback after flashback. It symbolises all the things that were wrong with my son's eating disorder treatment (although there were elements that were OK, but we're talking wrong here - potentially damaging stuff) and which, in my opinion, prolonged his suffering unnecessarily while making it ten times harder for me to play my role in helping him to recover.

The above are just some of the reasons why I hate BMI as an indicator of the severity of an eating disorder - or even, in some cases, diagnosis.

In other words, there are still some medical professionals and GPs out there (as a friend of mine can confirm) who believe that, if your BMI is above a certain level, then there's nothing to worry about.