Hatrack River Forum: Body Mass Index: Is it really accurate?

This is topic Body Mass Index: Is it really accurate? in forum Books, Films, Food and Culture at Hatrack River Forum.

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Posted by reader (Member # 3888) on :

I came across an article about BMI, and out of curiosity, plugged my height and weight into one of the BMI calculators that have proliferated online. My result: 18.1 - which is officially underweight. I have never gone on a diet in my life, eat nice big lunches and suppers (admittedly I usually skip breakfast, but that's just because I don't feel like eating in the morning) and in general do not avoid any kinds of foods in order to remain thin. So...would I really be better off if I weighed a couple of pounds more? Does it mean I need to excercise more? (I know that muscle weighs more than fat.) Is the BMI accurate for tall people? How can it be accurate altogether, if it is for both men and women? Also, if for some reason I lost a couple of pounds (I don't expect that to happen, as my weight has been pretty much stable for the past three years or so) should I actively try to gain weight? How does one go about gaining weight in a way that isn't unhealthy and won't put the weight where I don't want it to go?

Posted by PSI Teleport (Member # 5545) on :

I think it means that your weight needs to be composed of more mucsle and less fat.

Not that your fat or anything.

*removes foot from mouth*

Posted by mackillian (Member # 586) on :

BMI sucks my will to live.

Posted by FlyingCow (Member # 2150) on :

::sucks mack's will to live::

::resists temptation to make lewd comment::

::fails::

Posted by mackillian (Member # 586) on :

*thwap*

Posted by sarcasticmuppet (Member # 5035) on :

I'm not an expert, but I always thought the fact that the BMI doesn't take into account bone density or muscle mass, it's crud. I think you have to weigh yourself underwater or something to get a good reading.

Posted by J T Stryker (Member # 6300) on :

speaking as a wrestler who took his BMI daily along with his body fat %, i can say that the formula is fairly acurate. but unless you are a body builder or serious athlete, the index is a little off.

Posted by Raia (Member # 4700) on :

Does anyone have a link to this mystical thing I've never heard of?

Posted by Ryuko (Member # 5125) on :

It's not something you link, it's something you do... Basically they send a little zap through your body to tell you how much of it is made up of fat and how much is muscle.

Posted by Raia (Member # 4700) on :

quote:
plugged my height and weight into one of the BMI calculators that have proliferated online.

Posted by Book (Member # 5500) on :

There are all kinds've ways... I think there's a height/weight ratio, too, right?

Posted by imogen (Member # 5485) on :

Here you are, Raia.

(Edit: Ack! My BMI used to be 21, and now it's gone up to 22.6. I guess that's what happens when you're a shorty and gain weight)

[ March 08, 2004, 09:39 PM: Message edited by: imogen ]

Posted by J T Stryker (Member # 6300) on :

the best formula uses heigth, weight, and fat measurements that can be taken electroniclly or more acreatly by the pinch method with a special kind of tweezers

Posted by Phanto (Member # 5897) on :

16.3

Posted by Raia (Member # 4700) on :

[Kiss]

Thanks, imogen.

Posted by Book (Member # 5500) on :

It's incorrect if you're a fairly muscular person. If you lift weights, it'll show you as overweight, or close to.

Posted by J T Stryker (Member # 6300) on :

the online version that you put on here is just a tad off, unless i went from 11.6 to 20.4 in a week'n a half

Posted by imogen (Member # 5485) on :

11.6? Isn't that clinically dead or something?

If they are following the right formula (weight (kg) / height (m) squared ) it should be accurate.

Hmmm.
*Goes off on a BMI calculator comparison hunt*

[ March 08, 2004, 09:50 PM: Message edited by: imogen ]

Posted by imogen (Member # 5485) on :

This one gives me the same result. As does this one.

Posted by J T Stryker (Member # 6300) on :

11.6 isn't dead, it's a top of the line High school wrestler, who cuts alot of wheight(i was top 10 before i got hurt). I'm not knocking these formula's, I'm just pointing out that they don't work for me.

Posted by Jon Boy (Member # 4284) on :

For my BMI to be 11.5, I'd have to weigh 85 pounds. I'm six feet tall. There's no way that's healthy. I think your calculator must be inaccurate.

Posted by imogen (Member # 5485) on :

Hey Stryker - welcome to Hatrack by the way!

As mentioned previously, BMI doesn't work for athletes. The BMI system supposes a certain 'normal' fat percentage of body weight - so for those people with very low fat percentage and high muscle, their BMI will show them as overweight, or even obese, when they are not.

However, I am curious about 11.6: if anything, being a wrestler should give you a higher BMI, not such a low one. It seems likely that you got 11.6 using a different system.

For illustration's sake, a BMI of 11.6 would require a 6 foot man to weigh 37.6 kg (82.7 pounds).
Edit: pipped to the post by Jon Boy!

[ March 08, 2004, 10:05 PM: Message edited by: imogen ]

Posted by J T Stryker (Member # 6300) on :

It can't be that inaccurate, it’s the one that the IHSAA (Indiana High School Athletic Association) uses. Then again, I also have a disgustingly low body fat percentage.

Posted by imogen (Member # 5485) on :

Yeah, but a low body fact percentage would cause you to have a higher BMI.

I'm sure it's just a different test (not BMI at all).

Posted by J T Stryker (Member # 6300) on :

Ignore me, I'm so confused, I'm just going to bow out of this thread befroe i make a real fool out of myself (it's too late, isn't it).

P.S. I'm so glad i finally found a set of forums where the people are more intelligent than me, maybe I won't be as cocky from now on.

Posted by Book (Member # 5500) on :

Were you like a super buff wrestler or a super ripped one, or both?

Posted by Ryuko (Member # 5125) on :

[Eek!]

I'm apparently clinically obese according to the weight thing... [Frown]

But I'm going to assume it's wrong, being as a lot of my weight is made up of muscle... Or at least some of it is... I mean... You can't get your black belt without having at least SOME muscle, right??? [Cry]

I duwanna be obese... [Cry]

Posted by Jon Boy (Member # 4284) on :

I think making a fool of yourself is half the fun of Hatrack.

Posted by J T Stryker (Member # 6300) on :

Ripped and 119, i was confusing the BMI with the body fat %, like I said, ignore my comments.

Posted by pH (Member # 1350) on :

I don't know about BMI, but my doctor once told me that ideal weight charts and such become freakishly inaccurate when you're tall. I'm 6', and apparently the thing says I should weigh 170+ pounds (I'm currently 135). So I don't know how you can really tell how in-shape you are unless you do one of those underwater body fat percentage things.

Posted by imogen (Member # 5485) on :

BMI is generally accurate for most people.

Of course, that means it's inaccurate for others. [Smile]

The third calculator I linked to is on a quite interesting site - it has some other ratios and forumlas, as well as calculations of 'ideal' weight according to different theories. (Depending on the theory, mine is between 54 and 59 kg).

And they state that BMI is *not* always right - it's better just to listen to your body and eat healthily etc etc. Some people are just naturally bigger/smaller/whatever.

By the by, a low BMI does not always mean healthy either. I had a BMI of 20 for ages in highschool, but I was skinny-fat. Not a lot of me, but no muscle to speak of. I'm much healthier now with more muscle on me.

Oh and Stryker - I make a fool of myself on a regular basis. It gets to be kind of fun after a while. [Big Grin]

Posted by rivka (Member # 4859) on :

BMI is a good indication for most people. An indication -- not something to get crazy over. [Wink]

Body-fat percentage is a more meaningful number, but it's harder to get accurately. The dunk test is VERY accurate (but who wants to do that on a regular basis?); using calipers (the "pinch method") varies from very accurate (high-quality calipers, and experienced measuring person) to somewhat accurate (cheap calipers and/or inexperienced measurer); the electric zap test is highly INaccurate (and potentially dangerous, especially if you have a pacemaker or are pregnant).

Back to reader's question, a very low BMI means two things, probably. You could stand to get more muscle (and maybe more weight, but I would DEFINITELY talk to a doctor (or nutritionist) before attempting that, as you may not really be underweight) on you; and I will have to hate you now.

It's nothing personal . . . [Wink]

Oh, and welcome to Hatrack, JT. [Wave]

Posted by The Rabbit (Member # 671) on :

I think people are confusing the BMI (body mass index) with % body fat. They are not the same thing. A % body fat of 10% is completely normal for an athletic male. Professional bike racers commonly run between 6 and 7 % body fat. A BMI of 10, would indeed put you somewhere in the dead range.

To ask whether or not the BMI is accurate is a bit strange since the BMI is defined to be the ratio of your weight in kg to your height in meters squared, it is accurate if your height and weight are measured accurately. It does not however say anything about your percent body fat. If you get more muscle but don't gain weight, your BMI will not change. The real question how meaningful is the "normal range" for the BMI. The BMI gives a fairly broad range for "normal" BMI. I currently have a BMI of 19 which puts me kind of on the low side of normal but I could gain 30 pounds before I would be considered overweight. I have a very slight build and if I weighed an additional 30 I would be quite fat.

On the other hand, I used to weight about 15 pounds less than I do now (BMI of 17). At that time, I was suffering from a maladsorption disease and I do indeed feel much healthier now that I weigh a bit more. A BMI of 18 puts you just below the low end of normal range. If you are under 25 and have small bones, I wouldn't be too concerned about it.