Thoughts on alternative formulations of BMI (adjusted for frame size, sex, height, etc)?
Options
Replies
-
Tacklewasher wrote: »amusedmonkey wrote: »MarkusDarwath wrote: »amusedmonkey wrote: »the whole "BMI is not accurate" argument is based on a very small athletic group,
This is the common assertion, but it is simply not true. BMI does not scale accurately with height, such that tall people, particularly those with large frames, are more likely to be above BMI 25 at a healthy body fat percentage, and they absolutely do not have to be very muscular or athletic for this to be the case.
On the other end, you have short people, especially those of small frame size, who show up as underweight by BMI when they get toward the lower half of healthy BF%, without having to be in the athletic range.
Then there's also the inactive "skinny fat" people, especially among the elderly, who are fine according to BMI yet are at a higher risk BF%.
The group of people for whom BMI is a non-productive assessment is far larger than the sub-set of "outliers" claimed by BMI proponents.
What other measure that can be done reliably within seconds do you propose that would weed out the outliers?
The "New BMI" seems a bit better, as it accounts for height differently.
https://people.maths.ox.ac.uk/trefethen/bmi_calc.html
But there isn't one that will work uniformly. Our bodies are just not that homogeneous. The problem comes when insurance providers rely strictly on the BMI when deciding on rates etc.
I think the bolded is the key, which is why I think the logical response is - start with BMI as a general guide and once you get close to a healthy BMI, start adding in other measurements. Like waist measurement, waist to hip ratio, maybe spring for a BF% test if the numbers don't feel right to you.
Since no indicator tells the 100% whole story, don't throw them all out. Just add them all up, consult your doctor, and come to a consensus.
And I agree, the fact that the insurance industry has come to rely on BMI stinks.3 -
amusedmonkey wrote: »What other measure that can be done reliably within seconds do you propose that would weed out the outliers?
Good quality BIA devices are accurate enough to at least place most people in the right general range. So can calipers and the Navy calculation, but those take longer than "seconds" due to the need to take multiple measurements.
Pretty much any means to analyze actual fat composition is going to be a better health measure than proxy data with no actual composition component.
2 -
"MarkusDarwath wrote: »"amusedmonkey wrote: »What other measure that can be done reliably within seconds do you propose that would weed out the outliers?
Good quality BIA devices are accurate enough to at least place most people in the right general range. So can calipers and the Navy calculation, but those take longer than "seconds" due to the need to take multiple measurements.
Pretty much any means to analyze actual fat composition is going to be a better health measure than proxy data with no actual composition component.
I personally have issues with these methods as they don't tell you how much of that fat is visceral. In fact in some cases with calipers its better to have a higher body fat than a lower percentage with visceral fat since can't grab your visceral fat in calipers, and BIA doesn't tell the whole story. Short waisted people also get the short end of the stick in calculations that rely on waist circumference because they can be structurally thicker in that area without necessarily being fat. See? No one measure is perfect and all simple methods have more outliers than more expensive methods. I do like the modified BMI equation above. The difference for tall people isn't pronounced, but shorter people get a more fair estimation. As for insurance and BMI, yeah, that's too simplistic if they really do want to get a risk assessment based on weight, but that's probably a cost benefit kind of thing for them. I think that's the reason people are against BMI but not other methods that also have shortcomings, because it's actually used to determine important things in real life so whether a person is a true outlier, delusional, or simply wants to be overweight because they have assessed their risk as low, it's frustrating when they are pushed externally into not making choice.1 -
I think the bolded is the key, which is why I think the logical response is - start with BMI as a general guide and once you get close to a healthy BMI, start adding in other measurements.
The issue with that approach is, how do you define "close"? According to the BMI charts, I hit 25 at 189 pounds (I'm presently obese by any measure, no arguing against that). But according to my BIA scale and the Navy formula, which both also happen to line up well with BMI at my current size, my Lean Body Mass is around 173 pounds. To get under a 25 BMI, I'd have to either drop to less than 10% BF or shed a significant amount of lean mass. I'm trying to avoid loss of lean mass. I can say pretty confidently that while I'm pretty strong, I'm not carrying an overly large amount of muscle in comparison to my height and frame that would qualify me as a genuine outlier.
At my present LBM, a max healthy BF% of 25 would put me at 230#. 15% would be 204#. So again, if I were using BMI as a starting point, how close do I have to get to the chart range before I start examining actual body composition? 15 pounds, 40 pounds?
0 -
amusedmonkey wrote: »I personally have issues with these methods as they don't tell you how much of that fat is visceral.
True, though BMI doesn't even tell you if it's fat at all. Visceral fat does have some pretty specific indicators, like a large, round, yet taught belly. (I have much visceral fat. I need to lose probably another 10 pounds to get my blood sugar and cholesterol in line, then quite a lot after that to get into an actual healthy range.)
0 -
MarkusDarwath wrote: »I think the bolded is the key, which is why I think the logical response is - start with BMI as a general guide and once you get close to a healthy BMI, start adding in other measurements.
The issue with that approach is, how do you define "close"? According to the BMI charts, I hit 25 at 189 pounds (I'm presently obese by any measure, no arguing against that). But according to my BIA scale and the Navy formula, which both also happen to line up well with BMI at my current size, my Lean Body Mass is around 173 pounds. To get under a 25 BMI, I'd have to either drop to less than 10% BF or shed a significant amount of lean mass. I'm trying to avoid loss of lean mass. I can say pretty confidently that while I'm pretty strong, I'm not carrying an overly large amount of muscle in comparison to my height and frame that would qualify me as a genuine outlier.
At my present LBM, a max healthy BF% of 25 would put me at 230#. 15% would be 204#. So again, if I were using BMI as a starting point, how close do I have to get to the chart range before I start examining actual body composition? 15 pounds, 40 pounds?
I have no data to back this up, but my gut is telling me that if you would need to get down to 10% BF to get into the healthy BMI range, you are a way out there outlier. And the fact that it doesn't work for extreme outliers doesn't make it useless for everyone. But I could be wrong.
And I've never heard anyone say BIA devices are accurate for anything, just possibly useful to determine a general trend.
I haven't done nearly the homework you have though!2 -
MarkusDarwath wrote: »amusedmonkey wrote: »What other measure that can be done reliably within seconds do you propose that would weed out the outliers?
Good quality BIA devices are accurate enough to at least place most people in the right general range. So can calipers and the Navy calculation, but those take longer than "seconds" due to the need to take multiple measurements.
Pretty much any means to analyze actual fat composition is going to be a better health measure than proxy data with no actual composition component.
The Navy calc puts me at 13.8% BF. I'm around 20%. So, that's not a particularly good one to go by.
Even "good quality BIA devices" are affected by various factors, so those aren't particularly good, either.3 -
I have no data to back this up, but my gut is telling me that if you would need to get down to 10% BF to get into the healthy BMI range, you are a way out there outlier.
I'm 6'1" and broad shouldered/large frame (my fingers don't meet when wrapped around the opposite wrist). If I weren't fat I'd be built like a viking. I'm definitely above average for overall size, but my musculature in comparison to my build is nothing extraordinary. Usually, when someone suggests that only 'outliers' don't conform to BMI, they are talking about people who are highly athletic and approaching body-builder degrees of muscle mass. But the truth is that just being genetically large can put a person in that supposed 'outlier' range without possessing extraordinary musculature, because the math formula doesn't scale correctly for height.
And again, this math flaw doesn't present an issue in population studies, because in those cases one is looking at the average for a large group. People at either end of the bell curve for size who will be flagged inappropriately as either underweight or overweight will effectively cancel each other out and not throw off the average.
0 -
The Navy calc puts me at 13.8% BF. I'm around 20%. So, that's not a particularly good one to go by.
Even "good quality BIA devices" are affected by various factors, so those aren't particularly good, either.
Just curious, you're around 20% as measured by....?
I find it interesting that people who support using BMI vs BF% don't wring their hands over their bathroom scale possibly being 3 to 5 pounds off, yet if one suggests tracking body fat then suddenly a similar margin of error is unacceptable.
0 -
MarkusDarwath wrote: »I think the bolded is the key, which is why I think the logical response is - start with BMI as a general guide and once you get close to a healthy BMI, start adding in other measurements.
The issue with that approach is, how do you define "close"? According to the BMI charts, I hit 25 at 189 pounds (I'm presently obese by any measure, no arguing against that). But according to my BIA scale and the Navy formula, which both also happen to line up well with BMI at my current size, my Lean Body Mass is around 173 pounds. To get under a 25 BMI, I'd have to either drop to less than 10% BF or shed a significant amount of lean mass. I'm trying to avoid loss of lean mass. I can say pretty confidently that while I'm pretty strong, I'm not carrying an overly large amount of muscle in comparison to my height and frame that would qualify me as a genuine outlier.
At my present LBM, a max healthy BF% of 25 would put me at 230#. 15% would be 204#. So again, if I were using BMI as a starting point, how close do I have to get to the chart range before I start examining actual body composition? 15 pounds, 40 pounds?
So here is the thing and the part where you are making a small error in spite of the very well thought out arguments you've brought about (well, other than all fat measurement methods have bigger sized errors and more lack of repeat-ability than you seem to believe they do)...
Well, two small errors.
The first error goes on like this:
I am not a body building beast today. I'm just an average Joe. I have loads of lean mass and lots of fat. If I lose loads of weight preserving my lean mass I will now be in an overweight BMI but shredded.
Oh my. Here I am an average Joe in overweight BMI and shredded. Therefore BMI sucks.
Sorry Joe and wait a just a New York second.
If you manage to hit a weight such that you are at your contest ready 10% body fat (or whatever it is you're aiming for) WITHOUT LOSING LEAN MASS to get there (so that you're at an overweight weight)... ***you have successfully changed your physique****.
You are NO LONGER AN AVERAGE JOE!
In fact, if you manage to get to that 10% body fat while keeping a high weight and ALL the LEAN MASS you have now... you will be a BUILT BRO BEAST and will obviously fall in the super athletic lifting bro category where BMI is not a correct representation of your muscle mass!!!
And the second issue is....
For many years the rule of thumb was 4 parts fat to 1 part lean mass (this has been challenged recently).
Sure.
And while you're obese you might even manage to better that with some lifting and loads of protein.
But the closer you get to the overweight and normal weight range the more the ratio of fat to lean mass lost will change.
So you WILL LOSE LEAN MASS. Managing how to MINIMIZE the loss does not equal ZERO loss! (and if you DO manage zero loss you have seriously changed your body composition and HAVE become the built beast who qualifies for the BMI rule exception as discussed above)
Lean mass is not just muscle. It is also connective tissue. It is water, of course and even organs that may get less enlarged as you get smaller.
And the calves that you need to carry 300lbs all day long are just not the same size as the ones you need to carry 150lb all day long. You're going to have a real hard time keeping that size of calves going unless your training or sport specifically targets them long time every day!
And you're correct. There exist problems with BMI. Just not necessarily the ones you identify!
18.5 to 20 was introduced as normal mainly to accommodate shorter females and Asian populations (generalize much?). And yet you find 6ft tall people on MFP arguing that 18.5 BMI makes perfect sense for them while 5ft individuals are arguing that 28 makes them look too thin.
So here we come back to the simple fact that BMI, in conjunction with common sense and good practices, is a good enough FIRST SCREENING TOOL. A quick and good enough basic parameter checker. For most people.
Nothing more. Nothing less.
5 -
I am not a body building beast today. I'm just an average Joe. I have loads of lean mass and lots of fat. If I lose loads of weight preserving my lean mass I will now be in an overweight BMI but shredded.
Oh my. Here I am an average Joe in overweight BMI and shredded. Therefore BMI sucks.
Sorry Joe and wait a just a New York second.
If you manage to hit a weight such that you are at your contest ready 10% body fat (or whatever it is you're aiming for) WITHOUT LOSING LEAN MASS to get there (so that you're at an overweight weight)... ***you have successfully changed your physique****.
You are NO LONGER AN AVERAGE JOE!
In fact, if you manage to get to that 10% body fat while keeping a high weight and ALL the LEAN MASS you have now... you will be a BUILT BRO BEAST and will obviously fall in the super athletic lifting bro category where BMI is not a correct representation of your muscle mass!!!
Actually, 10% BF at my current lean mass would put me (just) -within- BMI. I have no need or desire to get that lean. I'm actually shooting for 15%, which would put me at 203# at my current LBM... overweight by BMI. And no, I would not look like a "lifting bro" at those stats. The last time my weight was that low was a few months after high school (-many- years ago) and at that weight I was just starting to not be skinny.
My actual goal is to actually add around 15 pounds of muscle at 15% BF for a total weight of 220#. And while I admit those stats will put me on the verge of athletic, it'll still be a far cry from being a body-building hulk. Having lost 15 pounds of fat since the beginning of the year (which of course takes up more volume than the same mass in muscle) I'm quite aware of how little visual difference 15# makes on my body.
No, I'm not "average" in that I'm big, and always will be, but in terms of musculature I'm just not that exceptional. BMI is claimed to scale with body size to only be incorrect in those with exceptional builds, but it does not.So here we come back to the simple fact that BMI, in conjunction with common sense and good practices, is a good enough FIRST SCREENING TOOL. A quick and good enough basic parameter checker. For most people.
Nothing more. Nothing less.
There's a big difference between using it as a first screening tool and using it to definitively say one is normal, overweight, or obese... or using it as a basis to set personal goal weights, as many seem want to do.
Despite the propaganda accusing everyone of being fat and delusional, most people don't actually need a measurement to tell them they could stand to lose weight. The question is not if, but how much, and BMI is just not the right tool for assessing genuine health risk levels.
0 -
My husband went for a check-up and weighed 1 lb in the overweight BMI range. He left his phone and wallet in his pocket and was fully clothed with pants, shirt and belt when he weighed. So a good 3-4 lbs of stuff. His doctor put a giant check mark on his paperwork that he was overweight. My husband was upset about it and came home talking about being too fat. He had actually lost 5 lbs since his last appointment, but that didn’t matter. Only that damn chart mattered.0
-
An internationally renowned scientist once told me that there is no significant mortality risk increase until BMI 30-35. His view was that BMI 25 is unnecessarily low as bar for “overweight” and is counterproductive.
I agree with this. I only really felt bad physically when I got into the obese range. I do think when you become obese your weight is a problem.0 -
Good idea but
1) wrist circumference is nowhere enough to determine your frame size. You might have thin limbs but a large ribcage, for example, or you might have fat on the wrist that will give you inaccurate results as well
2) the waist to hip ratio thing is just as flawed, as you might have a larger waist or smaller hips depending on your genetics.
So basing results on those two things is never going to be accurate either.
BMI is just a general indicator, and like other said, it really has a WIDE range to account for difference in lean mass. The truth is, in the end 5 lbs probably won't make a huge difference health-wise anyway...0
Categories
- All Categories
- 1.4M Health, Wellness and Goals
- 391.6K Introduce Yourself
- 43.5K Getting Started
- 259.7K Health and Weight Loss
- 175.6K Food and Nutrition
- 47.3K Recipes
- 232.3K Fitness and Exercise
- 393 Sleep, Mindfulness and Overall Wellness
- 6.4K Goal: Maintaining Weight
- 8.5K Goal: Gaining Weight and Body Building
- 152.7K Motivation and Support
- 7.8K Challenges
- 1.3K Debate Club
- 96.3K Chit-Chat
- 2.5K Fun and Games
- 3.3K MyFitnessPal Information
- 23 News and Announcements
- 938 Feature Suggestions and Ideas
- 2.3K MyFitnessPal Tech Support Questions