BMI, sex, and a new measurement

[ArabellaScott]

BMI is based on a white male standard (I hear your gasps of shock).

ABSI - (a body shape index) measurement that takes into account waist size will apparently help with more accurate idea of how our weight/size/shape will impact on health. Especially relevant for women, I think, whose body shape is different from that of men.

www.telegraph.co.uk/health-fitness/body/forget-bmi-new-formula-measure-health/

fatcalc.com/absi

Thought this was interesting not least because I am apparently healthier using this measurement than using BMI.

I know that waist size was being measured by GP surgeries to look at the amount of visceral fat. I'm much healthier by this measure than by my BMI.

Yes, I'd heard of using waist size before, but not this specific measurement, which has an acronym (always impressive) and spits out some sciencey looking calculations when you put your numbers in. [easily impressed]

It needs to be used alongside standard BMI as the cut-offs for that are different for some groups (e.g., SE Asians for whom overweight begins at BMI 23 not 25+).

Plus, there's uncertainty and probably some inaccuracy around standard collection of data and this disproportionately affects the estimation for post-menopausal women:

journals.plos.org/plosone/article?id=10.1371/journal.pone.0033308#pone.0033308-Okorodudu1

I'm persuaded of the existence of normal weight, metabolic obesity - and the fact that it can be present in people with a BMI of

Thanks, Embarrassing, useful clarifications.

Of course these are all incredibly rough and ready measures. But presumably refining them to be more suited to different groups is going in the right direction.

How do they arrive at a metabolic obesity measure?

@ArabellaScott

Thanks, Embarrassing, useful clarifications.

Of course these are all incredibly rough and ready measures. But presumably refining them to be more suited to different groups is going in the right direction.

How do they arrive at a metabolic obesity measure?

DXA scanning and other calculations. (These have their own problems for technical reasons, but those plus some MRI slices are useful. Birmingham Uni. did some excellent work on body fat volumetrics but it doesn't seem to be making any headway in the wider world.)

www.wmahsn.org/news/id/341

For me, it's an under-researched issue. The standard expectation is that metabolic dysregulation is associated with obesity and that age-related sarcopenia presents as obesity. However, when you explore the issue, there are people who are not recognised as at risk of diabetes etc. because they have an acceptable BMI but the visceral fat and overall body composition categorises them as metabolically obese.

I strongly suspect sarcopenia in women is much more common than realised - and below a particular level of lean body mass, the low amount of muscle will itself become a problem for the metabolism as it acts as a repository for glycogen etc. and affects your ability to handle above a certain number of calories in one meal.

If you're sarcopenic, and you end up eating a calorie level to maintain a healthier body fat level, with a low level of muscle, it is genuinely problematic to cover all of your nutritional needs within the amount of calories that keeps your weight stable.

The PLoS paper is worth reading even just for the introduction.

Figure 1 presents a scatter plot of BMI versus percent body fat. The upper left quadrant bordered by vertical BMI = 30% line and horizontal red line (women) or blue line (men), identifies the misclassified subjects who are non-obese based on BMI, but obese based on percent body fat. Examining these 39% (n = 539) of subjects in detail (see Figure 2), women had clear correlation between advancing age and % misclassification. 48% of women ages 50–59 misclassified, and 59% were misclassified by age 70+. This association with advancing age was not observed in men.

It's a recurrent irritation for me that when women have a fall and hip fracture over the age of 65, it's regarded as a sentinel event because within 6 months, an eye-watering number (I need to check) are unable to live independently again.

However, if women are not recognised as sarcopenic, this (by itself) increases the risk of fall and injury. I strongly feel the risks would be reduced if we had better assessment of sarcopenia at an earlier stage in life.

Ta! [nods sagely while googling 'sarcopenic']