The FastDay Forum

[janeg]

I recall debate as to the usefulness of BMI as a tool but I can't for the life of me remember any of the ins and outs.
Can anyone point me in the right direction please?
ta much

[carorees]

The problems with BMI include:
1. It takes no account of the muscular composition of the body (or indeed bones structure)
2. As height increases, the amount of non fat mass (bones, muscles, water etc) increase by a greater proportion, so BMI is particularly inaccurate for tall (or short) people
3. From the perspective of heart health, visceral (around the organs) fat is much more important than weight so BMI is not as good a measure of cardiovascular risk a waist measurement (or waist: hip ratio) because it cannot differentiate between visceral and subcutaneous (under the skin) fat.


There may be more but I don't know. Personally, I have always thought that because I have short legs and a long body, I should be given a little more leeway!

[janeg]

Cool, thanks Caroline. It's all coming back now! And as a shortarse I don't like it either!

Here's a proposed improved BMI that uses the same simple data (weight and height): http://people.maths.ox.ac.uk/trefethen/bmi.html

[carorees]

Fascinating reading Dominic.

I think, based on that article, it explains why muscular, tall, rugby players have been wrongly categorised as obese by BMI.

BMI is a useful measurement for the general population. Unless you strength train then your muscle mass will not skew the results.

The BMI measure is a value of weight proportionate to height. So if you are 160cm and 80kg your BMI is 31. Whereas if you 170cm and 80kg your BMI is 27. So what that is saying is that more of the 80kg in the person who is 170cm is attributed to lean mass.

Also visceral fat will be reflected in the BMI measure. Visceral fat has a mass so it will show up on the scales too. So if you have a lot of visceral fat your BMI will be higher. You won’t know how much is subcutaneous fat and how much is visceral fat but still it is reflected in the measure.

All in all I am pro BMI. I think it is a better marker than weight alone.

http://www.telegraph.co.uk/health/healt ... w-BMI.html drops me by 0.7 and I'm no longer overweight

@PhilT: yes, that is a reference to the same new method as my link

@Echo: this new BMI calculation still works by comparing weight to height but in a way that is more accurate for people who are taller or shorter than average - have a look at the links. It will still be skewed against athletes I think.

Both calculations put me at a BMI of 27, but then I’m of average height.

I don't think BMI is intended to be an exact science so I don't see the point in over complicating it.

If you want a measure of body fat then arrange to be measured. Then you'll know if your weight is attributed to fat mass or muscles mass.

Sorry for this dense question....how would I be able to find out what % of my body is fat?

It's a good question, I think. I found an article here http://www.builtlean.com/2010/07/13/5-ways-to-measure-body-fat-percentage/ about how to work it out - which makes it seem pretty difficult! I think most people who like to measure their own body fat percentage in the real world use a special type of scales such as the ones by Omron (http://www.omron-healthcare.com/eu/en/our-products/weight-management). I think Michael Mosley used these in the Horizon programme.

But they are not necessarily accurate - see piece here: http://www.medicinenet.com/script/main/art.asp?articlekey=56830. So where does that leave us? Probably just using BMI and waist measurements...

You can buy or borrow a fancy set of scales or the other way is that your wobbly bits are measured by someone with a pair of callipers.

I have the scales but I have forgotten how to use them since moving and I think I was half-fat anyway so...

Thanks both of you...I'm off to investigate the scales. Mine are clearly pretty amateur.

Interesting... As a tall guy that new formula dropped me from overweight into the top end of the "healthy" range. Strangely the lower end of the "healthy" zone seems much lower than the standard... I'm a narrow shouldered guy and I've still got quite a guy so I'm not going to adjust my target weight for now...

Here's a proposed improved BMI that uses the same simple data (weight and height): http://people.maths.ox.ac.uk/trefethen/bmi.html

Thank you. Just measuring ourselves is best. But doctors seem stuck on the BMI thing. Tried the link and my new BMI came out to a correct and healthy range for me.