Tuesday, September 06, 2005

BMI - Body Mass Index

Body Mass Index (BMI) is a rough guide to how overweight or obese you are. It is based on a formula that makes a connection between your height and your weight.

You have to go metric to make it work, but in essence you divide your weight in kilograms by your height in metres multiplied by itself (W/HxH)

However, if you don't want to mess around with conversion tables and a calculator, then I suggest you visit deathclock.com (if you click on that link it will open up in a new window) and scroll to the bottom half of the page. You can then select your height in feet and inches, and your weight in pounds and it will do the calculations for you. If you're feeling really morbid, then you can scroll back up and use the information to calculate how long you have left to live, barring fatal accidents.

So here are the Obesity Definitions:

BMI under 18.5: Underweight
BMI 18.5-25: Normal
BMI 25-30: Overweight
BMI 30-40: Obese
BMI 40+: Morbidly Obese/Extremely Obese/Grossly Obese/Pathologically Obese (these are all medical terms - who says there's no prejudice in the medical profession?)

This is only a rough guide, because of course athletes tend to fall outside these categories. For example, every member of the England Rugby Team would be categorised as Obese under these definitions, although the amount of fat they are carrying is negligible. However, for the rest of us mere mortals it does work as a rough guide to where we are at

Back in February, my BMI was 43. It is now 34 (as of September 6th 2005)


TC said...

I have the same bmi as you do! That is kind of cool!

Kim Ayres said...

Hi TC,

Sorry to say this post was written a year ago, somy BMI is now 29.

Anonymous said...

Sorry you subscribe to BMI. I think that's all a load of horse manure.

The first time I heard about BMI a health reporter on the local tv station reported that the height-weight ratios had been discredited as and thrown out, and were replaced by the BMI. It's pretty clear to me that BMI is simply a shirty height-weight ratio because it has that fancy square factor.

My wife and my sister are the same height. Neither is overweight in my opinion. If they stand back to back, my sisters shoulders are half again as broad as my wifes. My sister runs, bikes, swims and does triathlons for "fun", so she has some serious musculature on her. I don't think it is reasonable that they should aspire to the same weight, but that is what BMI says.

I would recommend you google "healthy whr". WHR - waist-hip ratio is a far better predictor of someones health, IMO.

Kim Ayres said...

Hello Anonymous - if you post again, please leave some kind of name so that I can identify you from other anonymous commentators.

As you'll see from the post, I clearly refer to BMI as a ROUGH guide, not a definitive one.

Muscle mass is heavier than fat, so if you are fitter then you will be heavier than your equivalent sized non-fit person.

It's all very well arguing the finer points of whether your BMI is 23 or 24 and what that means, but when your BMI is 43, as mine was when I began, you cannot kid yourself that it's excess muscle.

My journey is not, and has never been, one where I'm worrying about being 3lbs overweight. My journey has been about being extremely overweight and trying to move back within the realms of relative normality.

I can live with 20lbs overweight, but 120lbs overweight was ruining the quality of my life.

BMI was a useful rough guide when I began, but it doesn't run my life

Joe Bloggs said...

BMI is a meaningless quackery with no scientific basis. This so-called 'standard' was invented between 1830 and 1850. It takes no account of genetic factors or differences between body types. It smacks of fascism, to arbitrarily impose a pseudo-science equation of height over mass. I am training for my country's armed forces, and my fitness levels are good enough, but my BMI is 29 like yours, which quite ridiculously implies that I am 'overweight' and almost 'obese'. Just as well they will assess me on my performance during fitness tests and not on my BMI. Just consider that you could reduce your BMI to 'normal' by just living on cigarettes and coffee and not doing any exercise, and you would be seriously unfit compared to 'overweight' people like me. Are all rugby or American football players 'obese'? And weightlifters and bodybuilders too? Nonsense. Save it for the glossy magazines, quacks, contracted-out internet articles by people in India using rentacoder.com and cable television, and whatever else occupies your fancy during your mid-life crisis.

Kim Ayres said...

Hi Joe,

If you read my reply to Anonymous above you will see that I've already answered your comment - I have never said that BMI is a definitive measurement, I have acknowledged that it fails to take into account fitness and muscle, and that it means even less the lower you go.

However, when you start off with a BMI of 43 you cannot kid yourself that it's just because you're superfit.

I repeat, just in case you do come back and read the comments you leave, it served as a ROUGH guide when I began

Anonymous said...

My biggest issue with the BMI is that it doesnt account for gender. It obviously is not going to work for a muscle bound body builder. I doubt Arnold Swartenegger would think he is obese because of his bmi rating. That being said, a woman who is the same height and weight as a man is almost always going to have more body fat, since men have larger bone structures and more muscle mass. I know that there probably are exceptions to this, but this is generally going to be the case. I have heard this being justified because the bmi is a "range," but a woman who is at 29.5 is unlikely to consider herself obese in my opinion.

Kim Ayres said...

Anon - if you ever come back, please read my responses to comments above.

Me said...

Like you, I think that BMI is a good rough guide to how 'fat' someone is. Of course it doesn't allow for gender, age, muscle etc. It's good for groups of people (ie saying that 30% of people have a BMI > 25).

People criticise it, but what's the alternative? A formula using waist, height and weight would be a lot better, but is guaranteed to have powers which are not integers, so you'd need a scientific calculator to work it out, and probably 90% of the population would get the answer wrong.

We are living in a world where not all people can do simple things, 20% of the US population can't identify the US on a map. Until robots roam the planet taking pinch tests to measure fat percentage, BMI is a good, easy measure.

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