BMI is a very poor indicator of health risk - seriously, the old messed-up insurance charts that say that i, at just under five-three, should weigh no more than 115 are probably better. as for those home bodyfat machines? they're crap. measurement is better but if you REALLY want THE answer, you need to do a dunk test - expensive and a bit scary and probably not worth the hassle.
BMI is just a matter of math: it's height in inches squared divided by weight in lbs. that's it.
these two ppl are both 5'8" and 240lbs:
but according to the experts (who were clearly smoking crack at the time), they have the same BMI of 36.5 which classifies IFBB Bodybuilding champion Ben White as obese!
to get around that, they now say that BMI does not apply to the very old, the very young, the very fit, the very muscular, etc, etc, etc.
my own BMI is 37% which puts me near the far end of the chart for obesity. however, my actual measured bodyfat is about 27.75% "acceptable", just overweight (use the military bf calculator here: http://www.bmi-calculator.net/body-fat-calculator/ ). i used to be right into powerlifting and bodybuilding, so i have higher muscle mass (even now) than the average woman and my bones are distinctly denser (they show up on x-ray nearly white, instead of the shadowy grey normally seen in a middle-aged woman), both of which add significantly to my *weight* but not my *size*.
if you want health risk, waist-to-hip ratio is far more accurate and if you want to know a healthy range, just go with the "ideal" height-weight charts and pick a range, any range.
Last edited by threenorns; 04-13-2012 at 07:51 AM.
While we're on the topic of body fat can someone help me understand the math? We're going to assume that the BF% taken by my trainer is accurate (surely it's not, since it was just the electrical-impedance thing, but we're assuming here).
At 228, it read 40%. Trainer said she'd like to see it at 25%. So I need to lose 15% of my body fat, right? So how come that doesn't translate into 15% of my total weight? Like, how come I don't need to lose just ~35ish lbs? I have been puzzling over that one and I can't come up with an answer.
BTW, berryblondeboys, I've never seen a swear get past the filter before! I lol'd at "shits and giggles." Maybe I'm ruining things by pointing out the loophole, but... it made me laugh!
While we're on the topic of body fat can someone help me understand the math? We're going to assume that the BF% taken by my trainer is accurate (surely it's not, since it was just the electrical-impedance thing, but we're assuming here).
At 228, it read 40%. Trainer said she'd like to see it at 25%. So I need to lose 15% of my body fat, right? So how come that doesn't translate into 15% of my total weight? Like, how come I don't need to lose just ~35ish lbs? I have been puzzling over that one and I can't come up with an answer.
BTW, berryblondeboys, I've never seen a swear get past the filter before! I lol'd at "shits and giggles." Maybe I'm ruining things by pointing out the loophole, but... it made me laugh!
Someone else can better explain your question you pose (but basically, when you lose weight, you don't just lose fat - you also lose muscle).
But about the swear word. When I was typing it, I thought, "Well, the filter will block it out, but people will get what I mean". When I saw it wasn't filtered I laughed too as making it plural I guess never entered their mind as a possibility.
While we're on the topic of body fat can someone help me understand the math? We're going to assume that the BF% taken by my trainer is accurate (surely it's not, since it was just the electrical-impedance thing, but we're assuming here).
At 228, it read 40%. Trainer said she'd like to see it at 25%. So I need to lose 15% of my body fat, right? So how come that doesn't translate into 15% of my total weight? Like, how come I don't need to lose just ~35ish lbs? I have been puzzling over that one and I can't come up with an answer.
First, the math for where you are right now:
228 lb Current Weight x 40% Body Fat = 91.2 lb of fat
228 lb Current Weight - 91.2 lb of fat = 136.8 lb Lean Body Mass (muscle, water, organs, bone, etc)
Now, assuming you kept all your lean mass as you lost weight (which you won't, as berryblondeboys mentioned above):
Goal Weight X 75% (since you said you want 25% body fat) = 136.8 lb Lean Body Mass
136.8 lb LBM / .75 = 182.4 lb Goal Weight, giving you a loss of 45.6 lb
However, since you will lose LBM as you lose weight, those numbers will change. As an example, if for each pound you lose along the way 70% is fat and 30% is LBM (which I just made up... I don't know what the typical ratio is off the top of my head), here's the new math if you got to 182.4:
45.6 lb lost x 30% is LBM = you lost 13.7 lb of LBM and 31.9 lb of fat
136.8 lb LBM - 13.7 lb LBM = now you have 123.1 lb LBM
182.4 lb scale weight - 123.1 lb LBM = 59.3 lb of body fat
59.3 lb of fat / 182.4 lb scale weight = 32.5% body fat
You see why it's important to try to hang on to as much LBM as you can. At the same weight of 182.4, there's a difference of 7.5% body fat. You really can't hold on to all of it, but you can dramatically increase the amount you keep with strength training.
Last edited by Blueberries; 04-13-2012 at 10:17 AM.
Ah, that was super helpful! Thanks for explaining that. So I shouldn't expect a linear decrease in BF% alongside pounds lost (as if that were linear anyway, ha!). I doubt I'll be seeing 25% BF at 183 lb, so I knew there was something wrong with the way I am thinking.
weight loss is definitely not a linear regression - think about 10lbs:
at 250lbs, someone who loses 10lb typically is disheartened because they don't see anything happening. other ppl have a vague idea you've dyed your hair "or something".
at 150lbs, however, 10lbs is very visible. ppl comment and compliment.
at 120lbs, a 10lb loss is typically enough to have ppl asking if you're okay.
weight loss is definitely not a linear regression - think about 10lbs:
at 250lbs, someone who loses 10lb typically is disheartened because they don't see anything happening. other ppl have a vague idea you've dyed your hair "or something".
at 150lbs, however, 10lbs is very visible. ppl comment and compliment.
at 120lbs, a 10lb loss is typically enough to have ppl asking if you're okay.
OH yes I saw this so well.
It took going from 190 to 170ish for people to start saying something.
When I hit 140 I got lots of "OMG YOU LOST WEIGHT OMGGG"
Every five pounds down to 125 I got more comments. From there on every 2 or 3 pounds down to 115 I got comments.
When I hit 115 I was a size 2/4ish, I started eating a **** of a lot more and lifting heavier weights and lost inches to get down to a size 0. Now I get people yelling that I've lost more weight.
my own BMI is 37% which puts me near the far end of the chart for obesity. however, my actual measured bodyfat is about 27.75% "acceptable", just overweight (use the military bf calculator here: http://www.bmi-calculator.net/body-fat-calculator/ ). i used to be right into powerlifting and bodybuilding, so i have higher muscle mass (even now) than the average woman and my bones are distinctly denser (they show up on x-ray nearly white, instead of the shadowy grey normally seen in a middle-aged woman), both of which add significantly to my *weight* but not my *size*.
I don't know how accurate this is, either. This calculator tells me I have 23.5% body fat. I know that mine is higher than that. On the other hand, my BMI is currently 25. Considering, I could stand to lose 15-20 lbs (of fat), I find it fairly accurate *for me*. So, there is certainly no 'one size fits all' solution.
I also have a high amount of muscle mass and dense bones.
yeah - again, if you want *exact* numbers, then it's the submersion test you need. you go in a tank of water sitting on a swing. they lower you to your chin, then you have to blow out all the air in your lungs and they drop you right under the water. you then have to wait until they get a reading. basically, the more buoyant you are, the more fat you have.
but when it comes to ballparks or "by guess or by golly", the online calculator aligns much better with what i see. i'm a size 16 (comfortable) or a (tight) 14; absolutely overweight but not THAT bad. there is *no way* that puts me on the 3XL range for obesity like BMI does.
so in a few weeks, i redo the measurements and just go by the difference.
see, if i end up a size 5 weighing 140lbs, i'm going to be pretty darn lean - but according to BMI, i'll still be overweight (i use 5' 2-1/2" for the math)!
Last edited by threenorns; 04-14-2012 at 11:56 AM.
I don't know how accurate this is, either. This calculator tells me I have 23.5% body fat. I know that mine is higher than that. On the other hand, my BMI is currently 25. Considering, I could stand to lose 15-20 lbs (of fat), I find it fairly accurate *for me*. So, there is certainly no 'one size fits all' solution.
I also have a high amount of muscle mass and dense bones.
Whenever I do any of those online tests I get 23-26 percent (this one a shade over 26%). My body fat scale gives me btween 27-30 depending on the day.
From what I can see in the mirror? it is so hard to tell. Seriously, if you cut off the flab on my stomach (and I can almost roll it/tuck it in (see baker's photo of her tummy today and when I grab my stomach it looks the SAME just more stretch marks) and look pretty good. But when you have that big glob of loose skin, it's really hard to tell how much fat you have. I am guessing that between 25-28 is probably pretty accurate for me right now.
