My 1,000 word essay on why BMI isn't useful for a sample size of 1

hipari

paperpudding wrote: »

Leaving aside OP's chart - because I am not a graph person and I dont really understand what it is saying and it has obvious inaccuracies if it includes subjects with 0% body fat

I dont get the antagonism either.

BMI is a useful guide for the vast majority of people - and for those who are genuine outliers, this is obvious both to themselves and their doctors.

Does anyone really not know, or think a doctor would not see, that they are an elite body builder or an amputee or a person with dwarfism or 9 months pregnant or have a huge instestinal tumour or any other reason why standard BMI calculations would not apply to them??

So, sure, in OP's words, BMI is not a useful number for those n = 1 people.

No kidding.


My own n=1 - as a not very muscular middle aged woman with a BMI of 28 - both my doctor and myself and any casual observer could tell it wasnt an abnormal amount of muscle or a medical condition - I was plain old over weight.
am healthier now and less likely to develop weight related medical conditions, with a BMI of 23.

Agreed. BMI is a model that measures people, not math that can be proven in absolute terms. "Healthy" or "unhealthy" is not a binary, it's a model that gives guidelines that are relevant to most people. Since "healthy" isn't binary, there's not really a definite limit between "normal weight" and "overweight", those are constructs created as guidelines as well.

My own n=1: My current BMI is 33 and there is no question that I am overweight/obese. However, all body composition measurements I've taken (multiple), health professionals' estimations and my past experience indicate that my "ideal" or "healthy" weight would likely be at BMI 25-26, which would still make me overweight according to BMI charts. While in that case BMI wouldn't be exactly "correct" in that sense, there's no question in my mind that it's a good indicator of which direction I should take.

paperpudding

Hipari - yes I agree. The BMI chart is a spectrum not an absolute Yes or No cut off.

we sometimes see threads where people are saying I am fit, I go to the gym, I have lost weight but I cant get my BMI below 25.1 - as if somehow 24.9 and 25.1 were some massive difference and that 0.1% is going to change everything.


But, barring obvious outliers, examples as in my post above yours, the vast majority of people can be sure 33 is not a healthy BMI for them.


However, as I have stated on these threads before, there are sporty muscular young men who are quite healthy slightly above the official cut off point - ie with a BMI of around 26 -28

Not elite body builders - just fit sporty young men.

Again I was a not so fit 50 year old woman, not a sporty muscular young man - and I didnt need a doctor or a chart to tell me that the exceptions of 28 being upper end of healthy did not apply to me.

hipari

@paperpudding exactly. I’m fairly muscular (under the fat), with a large frame, wide pelvis (hip bones) and big boobs, so putting a healthy fat percentage on top of all that easily leads to a BMI that’s slightly over 25. From BMI 33 it’s pretty clear that there’s only one direction, but the distance to ”healthy” can’t be defined on exact terms.

BMI is a great indicator, not an absolute truth.

bmeadows380

I was one of those who was against the BMI for years until I finally got a grasp of what the BMI was saying and that it was a statistical average and was really communicating risk of health problems. I think it comes in to a common misunderstanding and miscommunication of the point behind the number for a given person - the common perception is that if you are above a 25, then you have to be "unhealthy" no matter how active or fit you really are. And medical doctors for a long time pushed that number; nowadays they seem to be getting away from using it as a hard and fast rule, or at least, its seems that way in my experience. I'm hearing a lot more advice on losing 5% of your current weight and not so much on the BMI number. Not sure about the insurance companies, though.

For me personally, I seriously doubt I'll ever make it to that magical 25 BMI; I"m getting older and I don't think I have the patience or the fortitude it takes to be super tight on your logging to lose those last 10-15 lbs. I can live with being in the "overweight" category; its still worlds healthier and a much better risk profile than what I had when I was stage III obese.

paperpudding

bmeadows yes of course it is about relative risk.

Being whatever your BMI is when you are 10 - 15 lb overweight is obviously less risk than being morbidly obese - and that is often presented in the incremental degrees of even losing 5% of your bodyweight decreases your risk.

of course if one is very over weight one would be advised to continue losing, not stop at 5%.
But every 5% is better than nothing.

NorthCascades

paperpudding wrote: »

Leaving aside OP's chart - because I am not a graph person and I dont really understand what it is saying and it has obvious inaccuracies if it includes subjects with 0% body fat

I dont get the antagonism either.

BMI is a useful guide for the vast majority of people - and for those who are genuine outliers, this is obvious both to themselves and their doctors.

Does anyone really not know, or think a doctor would not see, that they are an elite body builder or an amputee or a person with dwarfism or 9 months pregnant or have a huge instestinal tumour or any other reason why standard BMI calculations would not apply to them??

So, sure, in OP's words, BMI is not a useful number for those n = 1 people.

No kidding.


My own n=1 - as a not very muscular middle aged woman with a BMI of 28 - both my doctor and myself and any casual observer could tell it wasnt an abnormal amount of muscle or a medical condition - I was plain old over weight.
am healthier now and less likely to develop weight related medical conditions, with a BMI of 23.

Just a guess, but I think this (the OP) sets peoples' BS detectors off.

Mellouk89

I think waist measurement is a better indicator, at least for men. If you don't trust the BMI chart, measure your waist and find out if it's ok relative to your height.

paperpudding

Why would you not trust the BMI chart??

Or more correctly, using the BMI chart in context ??

Theoldguy1

Mellouk89 wrote: »

I think waist measurement is a better indicator, at least for men. If you don't trust the BMI chart, measure your waist and find out if it's ok relative to your height.

The waist measurement is another good screening tool. For the vast majority of people it's results as to putting people in categories will be the same as BMI measurement.