Top Reasons Why The BMI Is Bogus | Hacker News Reader

Top Reasons Why The BMI Is Bogus

npr.org

13 pointspeter12310 comments

The article is correct in that a very muscular and physically fit person can achieve a high BMI score, erroneously suggesting they are overweight.

But on the other hand, is there any risk at all that said very muscular and physically fit person is deluded into thinking he (it's almost impossible to be a female and get an "obese" BMI rating due to muscle mass) is actually obese?

While BMI is a very inexact measurement, one that can be flat-out wrong in many circumstances, people who have a "handful" of grabbable tissue on their waist should not henceforth blame their high BMI score on their excessive muscle mass.

I don't think the article is directed at people worrying about their own BMI, but when it is used by say, adoption agencies or insurance companies, etc. I seem to remember a case here in the UK where a couple weren't allowed to adopt because the man had a high BMI because he was a gym enthusiast or something.

I didn't think of that, quite honestly. You're quite right.

On the other hand, don't you agree that the actual problem in cases like that is rigid policy making with no regard for circumstances, rather than BMI itself?

It's both - basing policy on a bogus metric will almost inevitably lead to problems.

It spells disaster, for sure. But basing a rigid policy with no regard for circumstances on a decidedly non-bogus metric like body weight will lead to similar problems.

Actually, the BMI suggestions are profoundly out of step with cardiovascular risk and mortality risk data. So-called "overweight" BMI ranges are associated with the lowest risks.

http://scienceblogs.com/purepedantry/2006/08/bmi_is_not_a_go...

"We found 40 studies with 250,152 patients that had a mean follow-up of 3·8 years. Patients with a low body-mass index (BMI) (ie, <20) had an increased relative risk (RR) for total mortality (RR=1.37 [95% CI 1.32-1.43), and cardiovascular mortality (1.45 [1.16-1.81]), overweight (BMI 25-29.9) had the lowest risk for total mortality (0.87 [0.81-0.94]) and cardiovascular mortality (0.88 [0.75-1.02]) compared with those for people with a normal BMI. Obese patients (BMI 30-35) had no increased risk for total mortality (0.93 [0.85-1.03]) or cardiovascular mortality (0.97 [0.82-1.15]). Patients with severe obesity (>35) did not have increased total mortality (1.10 [0.87-1.41]) but they had the highest risk for cardiovascular mortality (1.88 [1.05-3.34])."

Still, if the proportion of people with high BMI changes, it has to mean something. I don't think the number is quite as useless as the article makes it out to be. But of course for individuals one might have to look at more parameters. It is just a rough guideline.

I've long thought that the only real benefit to BMI is psychological - it gives doctors a way to tell their obese patients that they need to lose weight in a way that is less likely to hurt their feelings.

Let's face it, if someone is fat, you don't need BMI to tell you that. The important point is that many Americans are fat, have a terrible diet, and need to lose weight - not that the fatness formula is slightly off and gives a few too many false positives.

So I'm not fat - I'm big muscled?

BMI suffers from the GIGO problem, since its inputs are height and weight. It is no more valid than the "height/weight" tables that were the fad previously.

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