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dr_tectonicHa! I knew it!
It is 9 am, and I have already been at work for an hour and a half, because today is the company health fair and I had a blood draw scheduled at 7:45. Oy vey. They had to stick me twice because I have uncooperative veins; now I know just to go straight for the expert phlebotomist.
Anyway, among the other health screenings, they have the nifty electrical inductance scales that calculate your bodyfat percentage. And now I finally have proof of something I have suspected all along: BMI (Body Mass Index) is a complete lie. (For me, anyway).
I weighed in at 232 pounds, fully dressed. I'm 5'10.5". Thus, my BMI is about 33 1/3. Even if we subtract off 7 pounds of clothes (my scale at home says I'm 225, naked) and round up to 71 inches tall, it's still 31.5. 30 is the cutoff for "obese". To have a BMI of 25, at the upper limit of the "normal weight" category, someone who's 5'10.5" is supposed to weigh between 175 and 180 pounds. (HA!)
BUT! The scale also measured my bodyfat at 27.7%. The attendant said she thought that was even probably several percent high (normal error is +/-3-5%) because I'd been fasting for 12 hours for the blood draw and I was likely a little dehydrated, so let's call it 25%. If I weigh 232 pounds and 25% of it is fat, that means that there are 58 pounds of fat in my body. If I lost ALL of them, I would weigh 174 pounds. So at 0% bodyfat, I would have a BMI of 25, just past the upper limit of "normal"! In other words, it's not physically possible for me to have a "normal" BMI -- not unless I lose a limb or something!
Still, I am kinda fat. How much should I really weigh? Well, if I dropped down to about 200 and the loss was all fat, I'd go from 58 pounds of bodyfat to 26 pounds of bodyfat. 26 out of 200 is 13% bodyfat, which is smack in the middle of the "healthy" range. 200. That seems like a totally reasonable number to me. So I think that will be my fitness goal. (Even dropping down to 215 would get me down below 20% bodyfat and into the "healthy" range.) Of course, the BMI for 5'11" and 200 pounds is about 28 -- in the middle of the "overweight" category.
If 14% bodyfat is the mean of the "healthy" range (for my age), and my weight at 14% bodyfat is 202 pounds, then the BMI for my "ideal" weight at 5'10.5" is 29.0. The mean BMI of the "normal range" is 21.75, which means that, assuming those mid-range numbers ought to line up, BMI is off by more than 7 points for my body frame. So really, my current BMI isn't 33 -- it's more like 26: a little bit overweight, not seriously obese.
I fucking KNEW it. Goddam population statistics.
It is 9 am, and I have already been at work for an hour and a half, because today is the company health fair and I had a blood draw scheduled at 7:45. Oy vey. They had to stick me twice because I have uncooperative veins; now I know just to go straight for the expert phlebotomist.
Anyway, among the other health screenings, they have the nifty electrical inductance scales that calculate your bodyfat percentage. And now I finally have proof of something I have suspected all along: BMI (Body Mass Index) is a complete lie. (For me, anyway).
I weighed in at 232 pounds, fully dressed. I'm 5'10.5". Thus, my BMI is about 33 1/3. Even if we subtract off 7 pounds of clothes (my scale at home says I'm 225, naked) and round up to 71 inches tall, it's still 31.5. 30 is the cutoff for "obese". To have a BMI of 25, at the upper limit of the "normal weight" category, someone who's 5'10.5" is supposed to weigh between 175 and 180 pounds. (HA!)
BUT! The scale also measured my bodyfat at 27.7%. The attendant said she thought that was even probably several percent high (normal error is +/-3-5%) because I'd been fasting for 12 hours for the blood draw and I was likely a little dehydrated, so let's call it 25%. If I weigh 232 pounds and 25% of it is fat, that means that there are 58 pounds of fat in my body. If I lost ALL of them, I would weigh 174 pounds. So at 0% bodyfat, I would have a BMI of 25, just past the upper limit of "normal"! In other words, it's not physically possible for me to have a "normal" BMI -- not unless I lose a limb or something!
Still, I am kinda fat. How much should I really weigh? Well, if I dropped down to about 200 and the loss was all fat, I'd go from 58 pounds of bodyfat to 26 pounds of bodyfat. 26 out of 200 is 13% bodyfat, which is smack in the middle of the "healthy" range. 200. That seems like a totally reasonable number to me. So I think that will be my fitness goal. (Even dropping down to 215 would get me down below 20% bodyfat and into the "healthy" range.) Of course, the BMI for 5'11" and 200 pounds is about 28 -- in the middle of the "overweight" category.
If 14% bodyfat is the mean of the "healthy" range (for my age), and my weight at 14% bodyfat is 202 pounds, then the BMI for my "ideal" weight at 5'10.5" is 29.0. The mean BMI of the "normal range" is 21.75, which means that, assuming those mid-range numbers ought to line up, BMI is off by more than 7 points for my body frame. So really, my current BMI isn't 33 -- it's more like 26: a little bit overweight, not seriously obese.
I fucking KNEW it. Goddam population statistics.
no subject
Date: 2005-02-09 09:54 am (UTC)no subject
Date: 2005-02-09 11:11 am (UTC)My opinion on BMI
Date: 2005-02-09 09:54 am (UTC)I'm the same weight I was in college. You remember me. If anybody tells me that I am on the very cusp of "overweight", I tell them they are out of their freakin' minds.
Re: My opinion on BMI
Date: 2005-02-09 10:00 am (UTC)It's stupid. Trust your own judgment.
Re: My opinion on BMI
Date: 2005-02-09 11:21 am (UTC)I'm not asking whether I'm fatter than I should be -- I know the answer to that question; it's "yes". The question that calculating BMI attempts to answer, though, is "how fat ought I be?" and it's that question that the BMI gives a totally bogus answer to. Now I have the bodyfat percentage answer, and it's actually useful information that has practical application to attempts to achieve greater physical fitness...
Re: My opinion on BMI
Date: 2005-02-09 12:39 pm (UTC)I can't imagine what body type it does take into account. Quinzee, maybe? It seems like a standard agreed upon by a board of fashion photographers for Vogue.
no subject
Date: 2005-02-09 10:24 am (UTC)The scales are cheap enough these days that you could easily get a larger set of readings to average among and, perhaps, get a more accurate picture.
BMI is nonsense, though. It presumes that everyone has the same frame and the same amount of muscle.
no subject
Date: 2005-02-09 11:12 am (UTC)no subject
Date: 2005-02-09 11:41 am (UTC)no subject
Date: 2005-02-09 11:48 am (UTC)no subject
Date: 2005-02-09 10:45 am (UTC)But...fat is stored in human cells, which have lots of water in them, even when they're fat cells.
So my vague understanding is that if you lost 58 pounds of fat, you'd probably lose a large amount of water by extension, and then be really, really thin.
In general, BMI numbers are weird, though. As I recall, it's basically weight divided by height squared. So if we assume [!] that people's mean "breadth" is linear in their height, then BMI is the mean weight of a horizontal cross-section of a person, times a constant of proportionality.
Once I started thinking about that, I basically stopped respecting the number, and went on with my life, worrying about eating good food, getting occasional exercise, and being able to fit into my pants. We don't own a scale.
no subject
Date: 2005-02-09 11:17 am (UTC)If I lost 58 pounds of them, that would be all of it, so I would indeed by very, very skinny. Ten of them, though, or 25 if I got super-athletic -- that's within the realm of reason.
no subject
Date: 2005-02-09 11:40 am (UTC)I read one paragraph toward the beginning as saying that they divide a person's mass into "fat mass" and "fat-free mass", and then estimate how much water is in the person, assume that their "fat-free mass" is 73% water, and do the obvious arithmetic.
But it's remarkable how hard it is to tease this down.
[And, the whole point of the paper is to indicate that all of these measures are statistically flawed. Though the entire paper is remarkably boring...]
Bleah. I'm bored just thinking about this.
no subject
Date: 2005-02-09 12:08 pm (UTC)Of course, I'll TAKE that extra point or two in BMI because for the first time in my life, I've got *curves*!
(Whic, BTW, is my other reason for being annoyed at BMI. Same for men and women? Bull!)
no subject
Date: 2005-02-09 03:05 pm (UTC)As it was explained to me, the first calculation is to split into Total Body Fat and Fat-Free Mass.
Total Body Fat includes adipose tissue (the stuff you want to reduce) plus necessary fat around the organs and on the nerves. Olympic gymnasts get down to 5%. Below 3% results in body failure.
Fat Free Mass includes bones, muscles, cartilage, organs, skin and blood. Of that, you want to keep the water percentage of the blood to be above 60%. You're quite right about the lean calculation. If you got rid of all your fat, you'd be 175 lbs. Required fat to live is 9 lbs, for a total of 184. If you exercise to lose the weight, you'll gain muscle and the number would be higher.
And 2 trainers and my doctor have told me to ignore BMI. At 5'7", my target weight is 181 to 194 lbs. with under 20% body fat.
And the National Institute for Health lists restrictions on the accuracy of the BMI.