BMI has "crucial shortcomings" as measure of obesity


#1

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#2

My first salaried job was as an admin assistant for an international nutrition project that was contracted for the Department of State. It didn’t turn into my lifelong interest, but I did learn some things about nutrition during my time working with people who held Masters and PhDs in the field.

BMI is a great tool for people who evaluate people in countries where malnutrition is an issue. There are more accurate measures, but very few that are as easy to implement. In places where calipers or ways to measure body fat are not easy to acquire, they can at least usually manage a scale and way to measure height.

It was developed not as a way to evaluate individual nutrition but as a way to evaluate a population. It may be a crude tool, but it has turned out to be a useful one for people in the field because it can provide data for every population. Having one measurement that can be utilized across all populations gives nutritionists a way to compare these populations.

It is not particularly useful for any one individual.


#3

I never knew that - thanks! I never put any stock in my personal BMI number because, at 6’ 2", it says that I’m normal if I weigh 145 lbs but overweight at 195 lbs. and I haven’t weighed 145 lbs since I was a really skinny 5" 11" 16 year old!


#4

We are fortunate enough to have the “problem” of measuring obesity and not starvation. BMI is good at measuring levels of relative starvation.


#5

In other news, water found to be wet.


#6

BMI was simply created as a basic proxy for body fat % because accurate body fat % measurements are very hard to produce compared to weight and height.

We’ve known it falls down for anyone who is athletic, tall or very short for decades.


#7

“BMI” posters are ritually abused with graffiti at gyms, for no other reason then its’ shear stupidity and lack of common sense.


#8

You know when you are overweight, you don’t need some scale to tell you.


#9

Arguably the greatest problem with BMI is that it scales wrong. Constant BMI increases weight as the square of height, but constant body fat or constant shape increase weight as the cube.
My favorite illustration of this is comparing NBA stars to 5’0"women. You can use BMI calculators to do the numbers but in short very lean 7’ 2"men have the same BMI as hugely obese short women .
BMI is, however, well correlated to life expectancy because being tall has its own health problems.


#10

I’m 5’ 9" just like in the illustrations but haven’t weighed 172 lbs. since high school (wrestling & gymnastics). I am barrel chested and have been blessed (cursed) with very broad shoulders and big upper body strength. (Figure 6 is pretty close).

I’m working to get rid of the spare tire and middle age spread but I can’t do anything about my body type. According to the BMI scale I am in the obese range (>30).


#11

I remember being in 5th grade or so, at a time when I was doing 1.5-2 hours of intense, coached, physical activity everyday (swim team and dance classes), plus daily gym classes, and my BMI being so “bad” that my gym teacher sent a letter to my parents warning that I was dangerously obese. It was clear to me at that point that BMI doesn’t mean anything useful. I’d love to be that fit now, when my BMI says I’m much less “obese” than I was then.


#12

Fucking ceiling fans are out to get us, I tell ya.


#13

In high school, I was 135lbs and 6’. According to BMI, that’s the bottom of “normal.” Which would be fine, except I could see my heart beat through my chest. Most people would call it “deeply underweight.”
Now I’m 6’1" and 215 (I know, I know… working on it…) and I’m within a breath of being “obese.”
Ugh. It’s not even close.
The lightest I can see myself getting without loosing meaningful amounts of muscle is maybe 185- and that’s still nearly overweight according to this.
I can’t help but think this is a useful tool being used for the wrong things.


#14

Ditto on other comments re: the difference between using measures for populations (e.g., nutritional epidemiology) vs. using measures for individuals (e.g., clinical practice). And ditto on this being old news about the limitations about BMI – it’s not a bad measure, it’s just not a perfect measure. Most clinicians will use BMI in the context of many other factors (e.g, family history of heart disease, diabetes, fat distribution) when talking to patients about the heath risks of obesity – you’re probably gonna have a different conversation with person #2 than you will with person #5.

On a random side note, why not “sort” the bodies in ascending or descending based on total body volume? It would make it much easier to see differences in body habitus across subjects. It also would make it easier to see differences between, say, folks with similar body volume – for example, subjects 1 and 6 have almost the same body volume but clearly have much different distributions of abdominal fat.


#15

Ten foot ceilings in the 130 year old house.
Eat your heart out.


#16

though their bodies look very different, they all have exactly the same body mass index

Selecting looks as a metric pretty much disqualifies a critique of BMI right from the outset. Ever heard of “body type”?

beach body

BMI is not about body aesthetics. If you are suffering from health problems induced by obesity, taking BMI as a guideline for weight loss is probably adequate for most people.


#17

I also forgot to add that a scale and a tape measure need very little training to use, as opposed to more sophisticated measurement tools. So, it also eliminates measurement errors which are a factor with more sophisticated tools being used by people who may have limited training.


#18

Plumbing will be installed in the fall, electric wiring sometime next year.


#19

Needs 3d scanning for body shape, which can be automated with a simple tool, and impedance measurement for fat percentage.


#20

Congrats!