BMI is easily misunderstood by people who know just enough to see that it’s imperfect, but not enough to understand why it’s still a valuable screening tool.
I’ve been in the “overweight” BMI range with low body fat before. It’s not too hard to get there if you’re lifting weights and paying attention to your diet consistently for years, but it takes a lot of work to get there. It doesn’t happen accidentally except for people who win some genetic lottery to build a lot of muscle and keep body fat low without trying.
Getting all the way to the obese BMI range while having healthy body fat is only happening for people with an extreme dedication to body building and diet (and let’s be honest, a lot of the people in this category are manipulating hormones too).
Yet whenever BMI comes up some people try to dismiss it as too flawed based on these possible edge cases. The edge cases for BMI exist, but that doesn’t mean it’s not useful. It’s a good general purpose screening tool with numbers that are available. If someone has more precise measurements available, those should be used instead. BMI is a really good first pass screener to determine if a closer look should happen.
People tend to think in absolutes. Even perfectly rational people fall logically foul to not considering outliers.
I am only 6' and only an intermediate lifter. I'm overweight, but BMI makes me look obese. It really only takes a normal person a year or so to get to three plates on squat with no supplements other than chicken broccoli and rice if they don't skip workouts. Assuming no injuries. That level of strength easily distorts bmi wildly if you are even a little taller than average.
And sumo wrestlers.
The line seems to be drawn at (effortful) activity level more than anything else. And BMI doesn't say anything about that.
I think the vexation comes from the focus on an attribute that is not directly mutable, per one's agency, because that's easier to sell things related to. Versus action that you have a lot more direct control over (social or physical circumstances notwithstanding).
(from https://en.wikipedia.org/w/index.php?title=Sumo&oldid=136533...), so I'm not sure this is a counterexample.
There's an enormous amount of wear-and-tear on their bodies, but the current cohort of wrestlers have access to much better knowledge about what's happening to them during their careers and afterwards, when compared to previous ones. During their prime years, they're objectively more metabolically healthy than the general population. Once retired, they're probably better able to manage their weight than earlier generations, and know to manage incidental issues like sleep apnea and alcohol consumption. I also wonder about the effects the tight-knit stables have on them, since we know positive and abundant social connection early in adulthood has ramifications later on.
>so I'm not sure this is a counterexample.
Yeah, don't just cite Wikipedia blindly. Some of the effects described seem strong, but there are caveats.
Anything to pretend they aren't too heavy.
In other words, for my height, I have a very long torso and very short legs. I think it should be relatively obvious that an inch of leg weighs significantly less than an inch of torso, so at a given level of body fat percentage, I'm going to weigh quite a bit more than someone my same height with more typical proportions, and thus my BMI reads me as more overweight than it otherwise would.
My point is not that BMI is bad or useless or anything else. My point is that it was designed as a population statistic and that it can be fraught when one tries to apply it to any individual with no nuance. A high BMI should cause one to consider and examine your health and weight. But it should not over-ride specific details about your physiology that point in the other direction.
It still functions well as a measure of load on your circulatory system, joints, you name it.
Your body is working harder than a typical 6'2" person, even if you have a great waist-to-hip ratio.
(But you'd still be better off with a smaller WTH ratio!)
I was also in the "overweight" category at one point while being low body fat. It was never a problem for anything, anywhere. I wasn't going to doctors who looked only at the BMI sheet and then told me to lose weight, because everyone could see that I was not overweight.
And I agree that it's never caused me problems, but that's because I and, as you suggest, doctors who look at the number, have understood that it's not that big of a problem in my case. That's what I mean by not looking at the BMI number naively and ignoring other physiological states.
I don't think anything you said conflicts with anything I said, and it sounds like we mostly agree.
Did you do that as a natural lifter? It’s hard for me to imagine most guys being able to get into the “overweight” range at < 15% body fat without some assistance.
For someone not working out or working a job that builds muscle, getting into the overweight category probably does mean they should take a look at their body weight.
The vast majority of natural lifters will never get enough muscle to really seriously throw it off.
Many active gym people have pretty high BMIs but fairly low fat (because muscle is dense), and unsurprisingly have better outcomes than the average person (if you ignore the share that uses/overuses anabolic steroids and co)
E.g. 20% bodyfat at 250lbs is still a lot of fat.
Of course it's difficult to ever get very high on absolute fat if at 15% or below.
Additional muscle is positive for health, but only up to some reasonable threshold. There is no health benefit to having very high levels of muscle, and in fact it may be negative for your health at extreme levels. E.g. many bodybuilders have trouble breathing, sleep apnea etc.
Both people in the example have 60lbs of fat. 1lb of muscle doesn't cancel out the negative health effect of 1lb of fat
1. https://www.cdc.gov/nchs/data/series/sr_03/sr03-046-508.pdf
As for 2, men in the US are getting shorter because of immigration which adds many confounders.
But also short people living longer has so many more possible explanations than less overall fat.
There is no word "heart" or any to this effect in the message you replied to so I did not understand that was what you were doing. I took your question as an attempt to attack the theory on the basis of prevalence of some heart conditions in shorter people.
https://medlineplus.gov/ency/article/003998.htm
"People typically lose almost one-half inch (about 1 centimeter) every 10 years after age 40. Height loss is even more rapid after age 70. You may lose a total of 1 to 3 inches (2.5 to 7.5 centimeters) in height as you age."
So people DO in fact tend to lose about 2 inches at age 80 versus their younger selves.
1. https://pubmed.ncbi.nlm.nih.gov/10547143/
2. https://www.mdpi.com/2072-6643/15/21/4694 (referencing the FHS there, the numbers are hard to find on the study's website).
The studies were conducted over different time periods when average nutrition changed, and demographics changed. And the study demographics just vary by location.
Height loss with age is incredibly well documented. Here’s a few more studies.
This is just basic medical textbook information. No one in the world is arguing that this phenomenon doesn’t exist.
https://pubmed.ncbi.nlm.nih.gov/32611342/
https://pubmed.ncbi.nlm.nih.gov/24962157/
https://pubmed.ncbi.nlm.nih.gov/10602346/
https://www.sciencedirect.com/science/article/pii/S266703212...
Again, from your OP: "so unless people naturally shrink 2" with age"
Are you denying basic science here, or what? Like, what is your deal?
It’s not the fat that kills. It’s oxidated lipids that kill.
https://www.sciencedirect.com/science/article/abs/pii/S24518...
From what I have heard from doctors, there is a clear sequence:
intra-organ fat (really bad) > visceral fat (quite bad) > subcutaneous fat (relatively harmless).
The nasty detail is that some people gain relatively more visceral fat than others. These three fats are correlated, but the correlation isn't the same in every human. Some have better metabolism and don't store as much fat inside as others do.
I’ve been in the overweight BMI category with low body fat by being active at the gym and focusing on diet. It takes some work to get there.
If I check the calculators for the obese BMI range, there was no way I could get there without either gaining a lot of fat on top of the muscle. The amount of muscle required to have an obese BMI with healthy amount of fat is absurd.
I think this is greatly exhaggerated.
Yeah you can put on as much muscle as Arnold and have a FFMI of about 27 then maybe have a BMI of 34 if you have 20% body fat.
But a very gifted natty might cap out at maybe 24 with a BMI of 30 at 20% bodyfat. But let's be realistic. This is not "many active gym people". This is the guy winning the local strongman meet.
Yes a couple of years training for most people can add a couple of points to BMI but I think people exaggerate how much this is. Go look at a 20lb brisket at costco - you don't see people with that much extra muscle all that often.
At 6 feet / 183 cm that it takes 184 lbs / 83 kg to be overweight. From what I could find, for regular gymgoers the typical weight for people around 6feet is 180-190lbs, which put many people around the overweight threshold. I am myself at 24.9, and while not skinny I am definitely in the skinnier half of the people at my local gym.
Yeah really well muscled guy being BMI 27 is probably ok but by 30 it's not natural muscles that are making the scales go up.
And obviously genetics matter, but it look at master level soccer players: athttps://pmc.ncbi.nlm.nih.gov/articles/PMC6239137/
I often wonder far from the median I am in this regard. I was under the impression that it was pretty accurate for assessing populations, but fell apart very quickly at the individual level. How many "normal"/otherwise healthy people do fall outside BMI's numbers?
BMI has known biases in gender, age, and race. It misclassified Asians, women, elderly w sarcopenia, and people with high body fat to lean tissue ratio.
The people most obsessed with "BMI isn't accurate" are overweight people making excuses for themselves.
I like to think of this as four quadrants around two axes. Low fat/low muscle is simply skinny. High fat/high muscle is the "big guy/gal" look that I associate with laborers. Low fat/high muscle is an athletic look; unhealthy in extremes (bodybuilding) but generally desirable. High fat/low muscle is skinny fat, which I associate with sedentary knowledge workers.
[0] And that, at least somewhat, tracks visual perceptions. Nobody looks at me with a shirt on and believes I need to lose weight, because 10-15lb isn't _that_ much extra on a tall frame. If I were 40-50lb overfat then that would be painfully obvious regardless.
My actual methodology is pretty crude though -- when I was 15lbs lighter I had borderline visible abs and other visual indicators of being around the 15-20% body fat mark, and aside from gaining weight I don't have any reason to believe I've had any notable muscular atrophy since then, so I'm estimating the actual excess fat in that ballpark. It's be easy for numbers to be off 10lb or more, but even then it'd still indicate the overfat surplus being much less than the overweight surplus.
A better methodology uses calipers and various skin measurements to estimate true body fat percentage.
But my target is to waffle around 20% or so on average.
"Overweight" can mean the same thing for weight, but it also refers to those with a BMI specifically between 25 and 30, and those with BMIs greater than 30 are classified as "obese".
It's specifically a high level of visceral body fat.
Genetics determines which parts of the body gain fat first as you gain fat overall, and some people have the unfortunate genetics to gain it first viscerally and some people have the fortune to gain it there last (and everything in between).
This means that you can have different people with the same body fat percentage but drastically different disease risks.
But yes this was also known already.
That's why it's been recommended to take a waist measurement alongside BMI to get a much more informative screening tool. Waist-to-height ratios are another alternative.