BMI ... Somebody posted a question on my fb page what is the difference between BMI & body composition
While those of us who know may scoff & laugh, it is, actually, a very valid question.
Dr's all use the body mass index as a guide or a measure for obesity general population all the time. Surely we should know what it means?
The fitness industry tends to use body fat measurements as a guide
So why the difference?
Well it would probably help if I gave you some info on both
BMI was first devised in 1832 by a Belgian mathematician/statistician named Adolphe quetelet.
What he was looking for was a way to define the "normal" man. His thesis was intended to describe the standard proportions if the human build.
The equation was largely ignored by the medical community until in 1972,a chap by the name of Ancel Keys published "indices Of relative weight & obesity" it was a landmark study of over 7400 men in 5 countries.
Keys considered quetelets equation to be the best indicator of body fat percentage & renamed it the body mass index.
Because it was simple & cheap to do compared to trawling through complicated historical data or studies or measuring skin folds, it began to catch on in the medical community.
However like Quetelet, Keys never intended the BMI to be used for individual diagnosis. It was only ever meant as a population marker.
It doesn't take into account gender, age, ethnicity, frame size or muscle mass ratio.
So how about body fat. What's so special about that ?
Well it's exactly what it says on the box.
Measuring the amount of body fat a person has in relation to the rest of their physical makeup
There are around 6 formulas one can use to calculate bodyfat if which the 3 Jackson pollock skinfold methods are probably most popular
The others are parrillo, durnin/wormersley & just the good old fashioned tape measure
The problem with these are that the person taking the measurements has to be very consistent & accurate.
The measurement site has to be exactly the same each time & so does the pressure in the calipers.
The advantage of this method is that it's cheap, relatively quick & if the practitioner is skilled, reasonably accurate ( enough for the general population anyway)
There are other ways of taking BF measurements. But these involve quite large & expensive machinery
Bio electrical impedance ( home machines are now available but notoriously inaccurate )
Hydrostatic weighing
Dual X-ray absorbtiometry
Air displacement plethysmography
The last 3 are very accurate but it's also hard to find somewhere that will do it
And they can be very expensive.
But do we really need to be that accurate?. Well for the general population no. Not all of us are physique competitors & athletes. All we need is a rough guide as to whether or not we are fat. Or rather our body fat percentage
This is more helpful in the indication of both health & obesity but doesn't tell the whole story. For this good old fashioned medical check ups & blood tests are still necessary
However in the search for reliable methods of assessing general obesity I have another idea.
2 really useful tools, ones I swear by, we all have access to & are dead easy to use
The mirror and plain common bloody sense 😀
