I thought this was pretty well known already. Being “overfat” is the problem, not being overweight (though they’re often correlated). BMI is really easy to measure, and is mostly accurate, that’s why it’s so pervasive. However it remains a pretty rudimentary metric (and really should use the third power or your height instead of the second).
> BMI is really easy to measure, and is mostly accurate, that’s why it’s so pervasive.
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.
At a population level, it's great. For individuals, it can fail in all kinds of ways. For me: it is not very good because my body has very strange proportions. I'm 6'2", but my waist is barely higher than my 5'1" wife, and my torso is nearly the same length as my 6'7" brother.
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.
Do you have a concrete example, though? Like an actual body fat percentage measurement that conflicts with what BMI explains for you?
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.
Body fat percentage can't conflict with BMI because BMI is not an estimate of body fat percentage.
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.
Yeah, people don't want to understand that your body structure messing with BMI is quite real but only a few points. It's unquestionably "wrong" in scoring me higher than my wife despite the fact that she's the one with a few extra pounds. But it scores us both as normal, the difference doesn't matter.
> I’ve been in the “overweight” BMI range with low body fat before. It’s not too hard to get there
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.
I suspect he was not nearly as lean as he suspected. Everyone over estimates how much fat they have to lose until they actually try to get shredded. My own efforts let me to discover that despite lifting weights in a dedicated fashion for years, BMI is still relatively accurate for me. Might be off by 15-20 lbs at the most, but still somewhat useful as a diagnostic tool since it if it says I'm obese, I am at the very least pretty overweight. It's only at the margin of overweight/healthy where it becomes only a tiny bit problematic.
The vast majority of natural lifters will never get enough muscle to really seriously throw it off.
Yes, sorry, I meant as someone lifting weights and working on it deliberately.
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 farther from average height you are the worse it is. If you are from some part of the world where the average height distribution is near the point BMI based itself you will perceive it to be so much better.
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.
>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 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).
It's complicated. If you actually look at the citations, they were looking at - and kind of necessarily so, if you think about it - a cohort of wrestlers who were born more than a century ago, and not later than mid-century; so, not the current generation. The article puts an emphasis on retained weight after retirement, head injuries, and extensively cites a Discovery Channel article from 2005 for many of the most damning claims (https://web.archive.org/web/20050831220303/http://discoveryc...), including the one about the sumo diet and weight causing metabolic syndrome - even though, earlier in the Wikipedia article, it's mentioned that more recent scholarship shows the remarkable (relative) metabolic health of active wrestlers.
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.
Yes, it is a pretty high level metric with good correlation a bunch of diseases, but really many of these is because it is ALSO correlated to percent of fat, which is often the more relevant metric. But as you said BMI is so much simpler to measure.
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)
> Many active gym people have pretty high BMIs but fairly low fat
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.
I do agree to some extent, but really the overweight threshold for BMI is 25. And 30 for obese.
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.
I very much disagree. Overweight starts at 25 BMI, and obese at 30. Most regular gym goers in my social circles maintain <20% body fat, and are classified as overweight based on BMI. In the US weightlifting is quite popular, and it’s not hard to gain enough muscle mass to classify as overweight. I’ve been “overweight” at 27 BMI going on >10 years now, with actual body fat fluctuating ~12-18%. I’ve had doctors tell me I need to lose weight because my BMI is too high, while I had visible abs. It’s a common theme among other casual weightlifters I know. I don’t think BMI is particularly useful for anyone that has done more than a year of basic barbell strength training cycle.
My completely made up rule is you get an extra point for every plate you bench (or squat etc). Its not a dramatic difference. If you bench 225 you’re not overwreight till 27 BMI, which iirc used to be the actual cutoff until they narrowed it.
Obese is hard. Overweight is easy if you walk, take the stairs, do the occasional pushup, and play something like hockey once week. Source: my entire life.
But specifically, it requires no gym time. Muscle mass is built with through reps not weight, and there are lots of non-gym-rat behaviors that do that. I'm not winning any comps.
> Many active gym people have pretty high BMIs but fairly low fat (because muscle is dense),
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.
Not sure I follow the logic here, but happy to be proven wrong if I'm misunderstanding. It's not intuitive to me that a 300 lb. person at 20% body fat is generally at the same risk as a 200 lb. person at 30% body fat.
Fat is inherently unhealthy for you beyond some low baseline level.
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
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.
Looking for some references on these claims, thanks! What you're saying registers as "makes some sense, but where's the evidence?" to me. I'm not seeing the connection where total lbs of fat is inherently worse than higher percentage.
The mean height for men at 20-29 is 69.2" and 80+ is 67.1" (measured in 2015-2018, the last data I've found) [1], which could be interpreted as shorter people having lower risk of all mortality. One could say that people are just getting taller over time and 80+ y.o. were shorter at their 20-29, but we also have the median height for 20-29 fro 1970s, when 2018's 80+ were 20-29 - it's actually 69.7" [2], men in the US are getting shorter over time, so unless people naturally shrink 2" with age the data points to shorter people having lower risk of death.
"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.
The actual studies [1],[2] that tried to measure this came to very different rates of height loss though: 3.6 cm and 6 cm from 40 to 80 in men. This does not look like a serious fact.
The difference was 3.6cm in the study that measured 10 more years 30-80. And 5cm in the study that measured 10 fewer years 40-80.
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.
I am not saying that. I am saying that the theory about absolute amount of fat being bad for health, as stated by the comment you responded, seems to be supported by data.
> I asked about the specific claim that absolute fat was bad for your heart.
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.
Some are more common in short people and some are more common in tall people. Hypertension is one of the ones more common in short people and is significantly more common than the rest combined, so your overall chance of having some form of heart disease goes down as you get taller. However, the forms of cardiovascular disease more common in tall people (e.g. atrial fibrillation) are more likely to actually kill you.
Do you have a citation for that? I've had thoughts in a similar direction (specifically around the upper/lower intervention points) but have had no luck finding data.
How accurate is it, in practice, for a given individual? I'm not that out of the ordinary proportion wise. I have a slightly longer torso and arms versus my legs, a somewhat muscular-ish baseline and broad shoulders, but I accumulate fat almost exclusively abdominally. My teenage self, lifetime peak of my fitness, no visible body fat, hyperactive football player, qualified as solidly overweight. If I was to listen to it, I'd be called obese before I noticeably start to show body fat.
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?
It’s a tool not the tool. If you have obese BMI you can… look in the mirror and see how accurate it is. If you aren’t sure take one of the dozens of other tests. People focus too much on it being a one stop shop - it’s not. It’s the start of a dialogue with your pcp and self on assessing your health that’s highly correlated with poor health outcomes.
I haven't been down in the normal BMI range since 8th grade. And I was measured at 6% body fat my senior year in high school! BMI has always run several points high for me. For that reason, I've always liked waist to height ratio better.
It's not really intended to be applied to individuals at all, but if you're in the "healthy" BMI range then you are probably fine just not thinking any further about your weight and doing something like measuring your body fat percentage would just be a waste of time and a source of stress for some people. If you're outside that range, then it is worth doing some of the more involved things to judge if your weight is healthy.
That was my impression as well. I'm just wondering if there are actual numbers to gauge by how much. I'd find it almost concerning anyone would draw any conclusions from it if it's not significantly any better at predicting health outcomes than a coin toss.
Another common misconception is that one is still healthy with high BMI that comes from having lots of muscle. It's not clear that lots of muscle is healthy.
Very very few people are in that category, and usually they have undiagnosed mental disorders. I don't even think it's possible to be leanish and have a BMI in the obese category from muscles without taking steroids or other products.
BMI is at best 66% accurate, so "mostly" is correct, but what is mostly good enough for?
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.
Yeah BMI is sort of a 'good enough' technique but also has some very obvious areas that it can miss. If you fall outside the typical fat to muscle ratio is a good example.
A muscular person can be "overweight" by BMI standards but not overfat at all. This is the case for many types of athletes, specially in strength disciplines but not only. It is the case in the fitness world that people ignore BMI and are intesterested in body-fat-percentage instead. This is hard to measure accurately so not so useful metric for the general population.
It's also possible to be overfat without being overweight! These "skinny fat" people often look normal enough but they carry very little muscle. It is a concerning condition because a doctor might not recommend a normal-weight person to hit the weights.
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.
The dominant discrepancies are "expected" fat (boobs, etc), and "unexpected" muscle (cyclists, body builders, hard labour careers, etc). I'm currently around 10-15lb overfat and 40-50lb overweight [0]. Only the former statistic matters.
[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.
In my mind, it's equivalent to subtracting a coarse estimate of how much extra muscle by mass I have compared to the median adult male they're using to construct BMI charts.
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.
Right, but what is the line of body fat percentage that you would consider "over fat", that's what I was curious about. I think it's implicit in your comment that it is maybe 20%.
Yep, that's right. Denominated in some fixed weight and any fixed fat percentage the delta is the same (e.g., if my weight is exactly 150lb or 200lb or 250lb and, at some concrete weight, I evaluate my real BMI at X and my naive BMI at Y, then the delta Y-X is independent of my target 20%.
But my target is to waffle around 20% or so on average.
I've been considered borderline or obese by the standard BMI index for 20 years at least, but for a lot of that had very little to no visible extra weight. A lot of that was just plain having more muscle than the average the standards are built around, but I also suspect BMI gets to be really inaccurate for tall people. I would look anorexic if I had to drop enough weight to be considered not overweight.
"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.
