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Georges

Fixing BMI: You're doing it wrong.

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So, I just read this : BMI Does the Body Mass Index need Fixing?

 

And my facepalm moment was when I realized that they weren't going to address (at all) the fact that if you look at every person out there who is, for instance, 5'10" and 175 pounds, then some of them will have too much bodyfat and some won't.  No equation that links a specific height/weight set to a set of {underweight, normal, overweight} will ever be a good measure of health.

 

(this post was a much needed vent.)

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Eh, any fix is an improvement.  Better fitting the weight:height relaitonship is a good start.

 

Though I'm not sure why they always strawman the BF% measure (really, there are no ways other than a dexa scan?), the US Armed Forces has a reasonably accurate formula that uses nothing more than a couple of measurements that is pretty quick and easy to take.  It would add all of like 30 seconds to a BMI measurements to turn it into a BF measurement.

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According to a bmi i did about 8 months ago i was "overweight" and borderline obese. I laughed really hard at this.

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According to a bmi i did about 8 months ago i was "overweight" and borderline obese. I laughed really hard at this.

 

I bet a significant % of men who have visible abs....are overweight by BMI.

 

I'm right in the middle of the overweight band. 

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Eh, any fix is an improvement.  Better fitting the weight:height relaitonship is a good start.

 

Though I'm not sure why they always strawman the BF% measure (really, there are no ways other than a dexa scan?), the US Armed Forces has a reasonably accurate formula that uses nothing more than a couple of measurements that is pretty quick and easy to take.  It would add all of like 30 seconds to a BMI measurements to turn it into a BF measurement.

The DEXA-scan is the only way to learn absolute body fat levels, and that's what they're getting stuck on.

Also, I have nothing to back this up, but doesn't the measurement method have poor interrater reliability?

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The DEXA-scan is the only way to learn absolute body fat levels, and that's what they're getting stuck on.

Also, I have nothing to back this up, but doesn't the measurement method have poor interrater reliability?

 

Sure, but the basic measurement menthod doen by the military was actually designed to be done on large populations and to be taken easily.

Similar traits to BMI in that respect.

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BMI is so useless that it seems like even an imperfect body fat percentage measurement would be better. According to BMI, my healthy weight as a 5'9" women is 130-169. But, I measure my bodyfat/muscle using a scale with the electric resistance pulse and according to that my lean mass is 130lb. If were 20% fat, which is fitness level for a woman, I would weigh 163lb - barely in the normal category. If I was an average/acceptable 25%-30%, I would be in the overweight category according to BMI. Even with an imperfect bodyfat score, these numbers are way off.

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BMI doesn't need fixing, it works just fine.  The problem is everyone is using it wrong.

 

BMI was developed to be used as a tool to use the average height and average weight of a population in order to be able to study social or environmental variables that might have made those people in that population, on average, overweight or underweight.  It is not meant to be used on a individual level. The individual builds of those within that population are averaged out.

 

This is why for a person of average build, BMI used on the individual tends to be a somewhat accurate assessment, but anyone who is of a rather slight build such as those who succeed in marathon running (coming in as underweight) or a large build like those very broad people or people with a bunch of muscle (coming in as obese) it is not accurate at all. For a large portion of the population it is not an accurate assessment of body fat, the further away you are from an average build for your height, the worse it gets.

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