Is Body Mass Index (BMI) prejudiced against tall people??

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Offline evan_au

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In this week's Naked Scientists podcast, one of the panel suggested that if you have two people of similar shape, their mass should increase with the cube of their height. This is derived from geometry.

This conflicts with the definition of the Body Mass Index, which is defined as (Mass in kg)/(Height in meters)2. This scale is frequently used to indicate obese, normal or underweight adults.

This means that tall people are more likely to score as "obese" on the BMI scale, because it only divides their mass by height2, when it should (geometrically speaking) be dividing by height3.

This same problem could result in obese short people not being reported as such.

See: http://en.wikipedia.org/wiki/Body_mass_index

Hmm... I wonder if the person who developed BMI was short or tall?

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Offline chris

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Re: Is Body Mass Index (BMI) prejudiced against tall people??
« Reply #1 on: 17/03/2016 08:19:33 »
BMI is a flawed measure for certain body shapes. A 100m Olympic sprinter, at the top of his or her form, would probably register as obese...
I never forget a face, but in your case I'll make an exception - Groucho Marx

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Offline alancalverd

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Re: Is Body Mass Index (BMI) prejudiced against tall people??
« Reply #2 on: 17/03/2016 19:29:55 »
...as would Arnold Schwarzenegger and even George W Bush (who was physically aircrew-fit, even if mentally unfit to clean his own office, let alone hold it). Problem is that even for "average" height people, muscle is denser than fat. At least that's my excuse.
helping to stem the tide of ignorance

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Offline chris

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Re: Is Body Mass Index (BMI) prejudiced against tall people??
« Reply #3 on: 17/03/2016 22:39:43 »
At least that's my excuse.

...for what??
I never forget a face, but in your case I'll make an exception - Groucho Marx

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Offline Colin2B

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Re: Is Body Mass Index (BMI) prejudiced against tall people??
« Reply #4 on: 17/03/2016 22:50:58 »
A number of studies have shown that waist hip ratio is a better predictor of mortality than BMI
eg http://www.ncbi.nlm.nih.gov/pubmed/16895897

Also higher VO2 max correlates well with reduced mortality risk.

(At least that's my excuse 😀)
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

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Offline alancalverd

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Re: Is Body Mass Index (BMI) prejudiced against tall people??
« Reply #5 on: 17/03/2016 23:07:40 »
At least that's my excuse.

...for what??
For having a BMI that upsets politicians.
helping to stem the tide of ignorance

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Offline Tim the Plumber

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Re: Is Body Mass Index (BMI) prejudiced against tall people??
« Reply #6 on: 18/03/2016 22:13:00 »
More prejudiced against strong people.