Body fat vs BMI

[Benjboi]

Hi All,

This is really posted on a discuss basis as I believe there are a lot of confusing ideas for people on what weight they should go for. I am 5' 11 and currently weigh 17st 11lb which is nearly a 2 stone loss for me from my peak and I've got my short term goals but my long term weight goal remains open. I have recently had my bodyfat calculated professionally and they put my body fat at 31% and my BMI is 31.1. Supposedly my BMI should be somewhere below 25 which would mean my weight should be 12 stone 11 lb as a minimum.

Now with a body fat of 31% that means my current lean mass is 12 Stone 5lb. If you assume that the lowest bodyfat I can realistically maintain is about 12-14% (with working behind a desk and no real desire to become a gym rat) which would mean as a realistic maintenance weight I would need to be 14 Stone assuming I don't put on any muscle mass between now and reaching that weight.

The point of all this is that with my circumstances as a guide and maintaining a 12% bodyfat percentage I would still be classed as overweight with a BMI of 27.3. Even using the guidelines of adding 10% to the BMI range for a large frame (my wrist measurement is just under 8 inches) I would still be at the very high end of the normal range slipping slightly into overweight range.

So my questions are 2 fold, 1) Is the way I am working this out correct? and 2) Is BMI really helpful in any way or should it be just ignored? I'm in the lucky position that I can get my body fat measured properly so understand the numbers that are behind these things but not all people are in that position. Even before I knew my bodyfat I knew in my gut that 12st 11lb was not a realistic goal weight for me and I think if I'd have listened to the 'professional' advice about my BMI I would have been seriously disheartened by this goal. After all if the chart says you're always going to be overweight then what's the point?

[LZeeW]

I am answering from the US, where we don't use stones, and all the conversions have been mind numbing. 

First, CONGRATULATIONS on your weight loss! 

Second,  BMI is just a relationship between height and weight.  It says nothing about body composition.  It is a starting point, something that has morphed into a screening measurement, and it has limitations.  I like tracking percent body fat over BMI.  I don't think anyone would think that you are overweight with a low body fat, even if your BMI is 27.

Third, 12-14% body fat range of fit, athletic men.  That would be VERY hard to achieve tied to a desk and unwilling to become a gym rat.  Percent body fat for "fit" men is 14-17%, "acceptable" men is 18-24%.  There are age adjustments.

You don't need to become a gym rat to be fit.  The buzz in some of the health news here is that being sedentary is the new smoking.

Get moving or keep moving, you are going in the right direction.

[whome]

Ditto to the above comment about "stone" - 

Also - you say "my weight should be 12 stone 11 lb as a minimum." - don't you mean maximum? The BMI calculator I looked at said you could get below 10 stone (140lb) and still not be underweight - 

Are you under the impression you are only going to lose fat weight and not some lean mass with it, that might be a problem in your calculations.

I was at 170lb when I decided I needed to get a handle on things but it was the cholesterol level that really got me off my lazy butt. Down from 240 in December to 156 in March - have a sore heal and had to stop running the last couple weeks and back up to 185 a couple days ago - I have got to get back to running soon - it isn't just diet for these numbers

BTW - what method was used for your BF% - water imersion, Caliper measure, Something else?

Good luck to you and keep at it - you can do it and no one else can do it for you

Craig

[Heybales]

BMI was created for looking at population statistics, only.

As what happens with many other tools, someone finds an easier though incorrect use of it, and now Dr's, insurance, ect all use it for individuals, which it was not designed to be used for at all.

If you view it as very rough idea of where you are at fine, but otherwise it's useless for exactly what you point out, and I know some lawsuits against company insurance providers because a lifter is being charged more for insurance because BMI is in overweight category.

And couple years ago in fact the official line for overweight or obese, don't recall which, was lowered so more could be included in that group, which of course allowed saying we have bigger epidemic, which of course allowed requesting more funding for that group. Ugh.

Don't worry about putting on muscle mass while on a diet - you won't. You can't.

And you should lose LBM even if you kept your muscle mass, because you need less blood volume for smaller body, less water stored for other things too.

[Kevin2]

Great discussion post! I'd only add that BMI was designed for people who are "average" in their height and weight. BMI statistics for us here in the US would indicate that the majority of American professional athletes will be obese...well, if you watch American football and look at some of our linemen, you might have the same conclusion! But many of those guys are not obese when you see them in their workout shorts and without their shirts. They're pretty lean and fit!

So...there are additional mesurements to consider. Waist circumference is another handy tool. Waist circumference should be under 40 inches for a male and under 36 inches for a female (please use your length conversions to suit your personal needs) to separate out obese from non-obese. Ideally, waist for a male should be under 37 inches and for a female under 32 inches.

Waist-to-height ratios are another consideration. There seem to be a variety of standards out there, and so you may want to check with your physician to determine the ratio that suits your particular situation the best.

Hope this helps!