I said very muscular, not extremely (IOW I’m not saying BMI works for everyone but mr universe; if you’re stacked you’re probably aware that BMI is not going to be that accurate for you. For the rest of us, it’s a fine guide).
Does that mean I’m implying that you must be stacked? Well, I had some difficulty parsing some of the numbers. Did you lose the 20 pounds prior to, or after, weighing 200 lbs?
160 lbs of lean body mass on a 5’10" frame seems awfully high to me, especially for someone that isn’t muscular. How did you arrive at that figure?
Here’s an empirical formula for lean body mass:
I was tested by a medical doctor specializing in weight loss. I was a patient under her care for about a year and she checked and logged my BMI and body composition at each appointment.
I went from 265 to 200 while under the care and supervision of this medical doctor. She checked my body composition with each appointment so I know that of the 65 pounds I lost, approximately 20 was muscle. 65 pounds is a lot of weight so naturally it was a mix of fat and lean mass.
So I only brought it up to say I was actually significantly less muscular than I had been previously. And I was never a body builder or athlete.
My point is that I think we should start with the axiom that if you are at a healthy body fat percent, you shouldn’t need to lose lean mass to reach a “healthy” weight. And if a metric suggests that to average people then it’s not very useful.
So sure, of course a 250 pound body builder with very little fat doesn’t do much to discredit BMI. But when it tells a very average 5’10" guy at around 20% body fat that he can’t realistically reach a ‘healthy’ net body weight without losing lean mass, it’s no longer a useful tool for determining healthy body weight.
OP’s question (“isn’t x[sup]3[/sup] rather than x[sup]2[/sup] the proper way to scale a linear dimension to mass?”) has intrigued me also, but it wasn’t until this thread that I was sufficiently concerned to Google it. 
Google took me to Wikipedia:
For comparison, I’m 6 ft 3, and though not ripped I’m muscular enough that sometimes people compliment me, ask me what sets I’m doing etc.
I weigh 185 pounds.
It’s got to be unusual for a 5 ft 10 guy to be packing almost that in lean mass alone. Even now with 160 + 40, you must be pretty stacked. Built enough to suspect that BMI is not going to be a very accurate measure for you.
I guess it’s just a question of degree and at what point you’re outside the norm and what point you’d expect to be within the norm. For instance, I still feel that if I’m not normal or average then it’s not a good metric.
I have to admit I was doing experiments with hypothetical women (just 5’5" arbitrarily and a woman’s body fat % guideline) and I wasn’t able to find a body weight @ healthy fat composition that was outside the BMI healthy scale for a net body weight, in marked contrast to how my own real numbers worked out.
It should be measured, but now there are many scales in the market which "calculate " it by asking for your height and gender and assuming a certain value for lean mass. Those numbers are about as trustworthy as the Enron auditors…
I’m 6’0, 225 lbs and I wouldn’t consider myself fat. My BMI calculation puts me into the obese catagory, but just barely. It does make me concerned about my weight even though it’s gotta be mostly muscle as I don’t have a gut or anything.
I think there are also some scales which use body electrical conductivity as a proxy for fat percentage. Which is better than making assumptions based on height and gender, but I don’t know by how much.
I always wondered how accurate that is.
Not bad but it vaies by ethnic group some.
If you’re in real good shape, then the BMI becomes less useful. Get your body fat percentage measured to get a better idea of how much excess weight you have.
I’m a hair above 193 centimetres and weigh 68 kilograms, which Google tells me is about 6’4" and 150 pounds. If this BMI calculator is correct, that means I’ve got 18,3 on the BMI scale and am in the 6th percentile of weight for my height. I wonder, does anyone have any sources for the kind of problems I may develop by being underweight?
I occasionally jog, when the mood takes me, but mostly I do a lot of walking and standing straight for hours at work. I’ve never been in the habit of going to the gym. Are there any particular muscle groups that I should be paying attention to? I mean, I can understand a man with a solid gut should pay attention to his back and knees, but I can’t think of anything I might be harming muscle or skeleton-wise.
BMI is a very rough indicator used by the medical profession and the diet industry. It gives an approximate measure for most people of average muscular build, average height and activity level. The BMI calculation would term many elite athletes obese because they have greater musculature than average.
There is a misconception that tall people are not scaled up versions of short people on average. Actually if you measure bones sizes they are. What society tends to do is over-feed short people and under-feed tall people. Since when did portion sizes in school or at a restaurant vary according to the CUBE of person’s height?
Then the everyday objects we have to move - books, shopping, furniture etc. all weigh the same regardless of a person’s height meaning that the shorter person is getting a more intensive workout than the tall person in everyday life (muscular strength is proportional to the square of one’s height, on average).
Tall people tend to have a lighter build than the scaled up short person’s build, on average, because of these factors. Hence when devising and promoting the BMI system, the square is used rather than the cube because 1) it is simpler 2) it is good enough in most cases and 3) because of the factors above, measurement suggests that the power is actually around 2.6 and who is going to be working that out?
The BMI’s singe biggest weakest is that it takes no account of muscular build. Hence a well-built, healthy lean person can appear obese according to the BMI, while the BMI figure can hide an ultra-light muscular build which is actually obese (in terms of very high proportion of body fat).
So please stop these “I’m 6ft x and weigh x lbs and I need to lose some” because without the weight of your muscles, it is practically meaningless to other people. Someone of the same height could easily be 20 lbs heavier and need to gain weight to be healthy!
Huh…really not the way I thought you were going to go with that post.
BMI is a rough, back-of-the-envelope figure and is useful in the same way that other rough measures are useful.
If you’re 5 ft 9, buy XXL clothes and are not a bodybuilder… chances are you could do with losing some weight. BMI is a measure on that sort of level of precision.
As far as the OP goes, BMI is still just a variation on height-weight tables. It can be useful as a rule of thumb and is probably sufficient as a quick screening tool.
The biggest advantage to the squaring part of the formula is that is puts the result in a wide range of integer values which makes for a nice chart. You could easily just say divide weight in pounds and divide by height in inchs and have a cut off for underweight, normal, overweight and obese. The values would just be in range of 1 - 5 and you’d need a couple of values after the decimal versus BMI where you get values in the 14 - 60 range and you can round to whole numbers.
I’m not really sure that ease of calculation is relevant… How many people actually calculate their BMI? Most folks will either look it up in a table, or go to some website that calculates it for them, and in either case an exponent of 2.6 would be just as easy to implement as 2.
If you’re going to change BMI, there is good research suggesting that waist to height ratio (WHtR) is a better predictor of health outcomes than BMI. WHtR is calculated as waist circumference (measured midway between the lower rib margin and the iliac crest) in centimeters divided by height in centimeters. It avoids everybody’s favorite pitfall of BMI, “but I’m a huge muscle man, that’s why my BMI is 30!” (even though I can guarantee that 95% of people with a BMI of 30 do not have it because of extreme musculature). WHtR emphasizes excess adipose tissue (fat in the gut) which is more highly associated with poor health outcomes than other fat, such as on the hips.
I do always find these BMI discussions a bit funny, because they always bring out all of the people complaining that BMI isn’t perfect, and it doesn’t apply to them or their cousin, etc. What is completely lost is that the US (with Europe and Australia close behind) are looking at a huge obesity epidemic regardless of how it’s measured.
Exactly right. It is an easy to use screening tool and both the tendency to use it as the gold standard definition of adiposity and the tendency to totally dismiss it because of its imperfections are equally misguided.
Yes, someone with normal BMI can still have a high level of adiposity and some who are overweight by BMI have very little body fat. But across a population it will flag those who have excess adiposity relatively well.