> Is body mass index a reliable method to categorise weight?
If by categorize you mean pigeonhole--then yes.
It seems to be a favorite of health care professionals.
I assume that's because it's quick and easy.
It's a number/category generated by knowing only height
and weight and is therefore limited by its own simplicity.
My personal favorite is bodyfat percentage.
Obviously it's not quick and easy like BMI, but when done
right it's a much more realistic piece of information.
Although not as high ranking as bodyfat percentage in my book,
my favorite quick and easy measurement is waist/hip ratio. I
prefer that to BMI as it's more specific in its intent.
An extension of waist/hip ratio is the measurement of other
body parts. I find waist/hip ratio, other body part
measurements, and scale weight together form a fairly
decent and easy to obtain picture of whether or not
ones diet is helping or hindering their situation.
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