Yet another reason to hate the BMI

According to The Metro, this elite female body builder was told by an NHS nurse that she needed to start dieting immediately and get more exercise, based simply on the fact that her body mass index (BMI) classified her as ‘overweight’. She was at the medical clinic to get contraception, and had not asked for any nutrition or lifestyle advice.



26 thoughts on “Yet another reason to hate the BMI

  1. Should we hate the BMI or this absurd use of the BMI by a nurse who clearly needs to do a better job learning her/his profession? Or is it that the BMI is so wrapped up with lazy, unimaginative health care service that it should just be abolished completely?

  2. I actually raised those particular questions because they’re very salient in the issues surrounding psychiatric classification. I continue to be amazed at the inappropriate ways certain service providers (sometimes doctors, sometimes nurses or even social workers) use a few psychiatric diagnoses that are, from a scientific or medical perspective, instruments that aren’t necessarily problematic on their own.

  3. I think the problem is that the BMI is way too blunt and inaccurate as a means of assessing whether someone is under or over weight. And to say that healthcare folks should use their judgement is to say that they should ignore the BMI in some cases. But that points to the problem – it’s inaccurate and should be ditched.

  4. Monkey nails it. Take ‘hate the BMI’ as shorthand for ‘hate the way in which the BMI is typically deployed in delivering healthcare to individuals’ (which is the context in which most of us will come into contact with it). The BMI may well have value as an epidemiological tool – it might, e.g., be a good way of getting some information about entire populations. But it’s crap when applied to assess the weight of particular individuals (and give advice based on that assessment), which is how it’s typically deployed in medicine.

  5. It seems that the solution is not to ditch the BMI, which still tells us something useful about health, but to understand that it does not apply in specific cases. It’s not a useful guide for evaluating the health of bodybuilders. Bodybuilders are shaped weird. We should not be criticizing the tool but rather the nurse who wielded it incompetently. It would be strange to get mad at wrenches just because some carpenter told us they were a good tool for driving nails into wood.

    I’m loath to ditch any tool that helps us combat our obesity epidemic, and all the negative effects on public policy and the environment that come along with it.

  6. Rachel – yeah, obviously the BMI’s uselessness for athletes (among many others) is well-known and well-rehearsed. This seemed comment-worthy because it was an instance of a medical professional so unwaveringly attached to the BMI that they told the woman in that photo she needs to exercise a bit to get fit. That’s taking it up a level.

  7. Here’s the thing: did the health care worker know that she’s a bodybuilder/athlete?

    I’ve had that sort of comment quite a bit from health care workers (I’m just shy of 6’0″ and 190lbs), but when I tell them that I’m an athlete and I train 10-20hrs/week, they stop saying those sorts of things. So I’m not so sure this is any different (unless, I suppose, the nurse knew that she’s an athlete). Athletes get this *a lot*.

  8. HappyPhilosopher – you’re assuming that the BMI is a useful tool for assessing the over or under weight-ness of non-athletes and that there is no other such useful tool, but both of those assumptions are false. There’s quite a good summary of the situation here.

  9. It’s true that it’s not the best measure; it is, however, probably the best one that can be calculated in a matter of seconds based only on information that most people have readily available about themselves. But many things in medicine are like that: it’s better to have both a rule of thumb that one can apply to lots of people for initial triage purposes and a collection of more discriminating methods that can be used for follow-up, if needed, than to rely solely on tools that are very exact but too complex and cumbersome to be used on large numbers of people. Of course if one loses sight of the limitations of the initial rough method, one will have unwanted results — but that’s a problem with the implementation, not the tool itself.

  10. I agree with Interested Grad Student. I would like to add though that one of the things which gives this incident the feeling of ‘ridiculous application of bmi’ is that there is a picture of this woman looking incredibly healthy, and we are brought to think ‘how could someone possibly tell her to loose weight and get more exercise on the basis of a silly measurement like bmi’. However, bodybuilders go on year round bulk/cut cycles where they put on a lot of weight outside of competition season and then cut off the fat before competing. Bulking does, in almost all cases (for natural bodybuilders at least) involve putting on a reasonable amount of body fat. It is thus entirely possible that this woman looked nothing like she did in that photo when she was being examined. The photo was almost certainly not taken during a bulk. Thus, the nurse’s initial judgement may not have been quite as ridiculous as it initially appears.

  11. When I was being treated for my anorexia for the first time, the BMI was the main tool of assessment they used. It was hugely damaging to me. It replaced one obsessive, unrealistic and unhealthy means of self judgment with another. Needless to say, I didn’t get better.

    I would love it if the BMI were abolished, I think it’s dangerous.

  12. Though I’m attracted to distinguishing between a neutral instruments and those that misuse it, I suspect this is not necessarily a wise distinction. The instrument becomes one only because it is embedded in a system of charts and, unfortunately, human values.

    At the same time, removing the instrument or algorithm does not remove the values, which may become even more blind. I think the AMA should issue an order that those without extensive training should just shut up about weight. A number of life saving drugs cause weight gain and it is really too much to be taking a drug which helps protect one against a cancer recurrence and then have to suffer inane lectures about losing weight.

  13. The problem is that obesity is a pretty huge problem at the moment. For many obese people having a checkup and being told by a medical professional ‘look, you need to eat better and get more exercise’ might just be the stimulus that they need to actually make a change. If people just shut up about weight unless they are absolute experts then this will not happen. Likewise, it is unlikely to happen if nurses are not allowed to use heuristics such as the bmi. People having to suffer through inane lectures about losing weight might just be the lesser of two evils in this case. The practice may be annoying, uncomfortable, and perhaps even slightly humiliating. However, if it saves (or improves) lives then it is surely worth it.

    Of course, I agree that the situation could be vastly improved by use of a more accurate heuristic (for example a body fat% measurement?).

  14. Body fat measurements are more accurate, but most people don’t have a fat caliper lying around the house, whereas scales are ubiquitous. One of the great advantages of the BMI is that you can figure it out yourself and, on the basis of some ceteris paribus rules, realize that it might be worthwhile to consult a medical professional about your weight. Of course, in some cases the cetera aren’t paria, and a competent medical professional will take that into account. But, for purposes of public medical awareness, at least, body fat measurements can’t plausibly replace BMI; in this role, BMI is like the standard blood pressure norms, or the appendicitis triad, or the canonical signs of stroke: it’s not perfect, but if properly applied it will give most people a quick and easy way to decide if further investigation by a professional is warranted.

  15. Interesting thoughts, although is there reason to think that people check their BMI and then consult a medical professional if it’s too high? I’m also under the impression that the BMI is more skewed than the rules of thumb mentioned in comment 16 above? But maybe I’m wrong about that.

    Good point about body builders and bulk.

  16. As I look at discussions on other posts about abuse and harassment, I can get quite worried about how philosophers think about people changing behavior. It’s as though we think that if you put a bit of information at people’s disposal, their behavior may change. Sometimes this is true; I’ve been reminded of this when my dear partner has tried to outline just what I should do about my recently operated upon knee. He is a lab director and when he puts some information before the members of the lab, by and large their behavior changes to accommodate it. But at home, when he tries this with our son or me, we look blankly and think, “Why should I believe this? Do I want to do this rather than what I was planning to do? What are the consequences of just going along with what he thinks” etc, etc.

    Our discussions of bystanders and what they can do have been brilliant, I think. I don’t know if we’ve really tackled how to change the perps, but that’s obviously much more fraught.

    What about losing weight?

    Getting other people to change their behavior and behave more wisely is very, very difficult. It is empirically possible that a bit of information about one’s weight would change one’s behavior in a very constructive fashion. However, the gap between a few things said and losing weight is very large. It is very hard to lose weight and keep it off; we often are effectively clueless, and many people make a lot of money by misinforming us. For this reason and others, if one is simply reacting to some bit of data or a small episode of nagging, the chances of making serious mistakes are pretty high.

  17. While I appreciate the possibility that a bodybuilder could have been in a bulking phase, there is clear evidence that people with large amounts of muscle will show up with an “obese” BMI, since it’s essentially a glorified height/weight chart.

    I think if we want to look at the relationship between obesity and health, the BMI is far too blunt of an instrument. It has two problems: not all obese people are unhealthy, and lots of non-obese people are unhealthy. Some Canadian researchers have started to clarify when obesity is a health concern: This focuses on research that predicts the outcome for individuals (not just populations) and also focuses on where the cause of the health issue actually lies. In otherwise healthy people, obesity is not obviously a problem.

    What’s particularly helpful on their approach is that dieting can often create problems. The vast majority of people who diet to lose weight will end up weighing MORE than when they started. Here’s an interesting TED talk that deals with some of the neurobiology of diets and how it can be problematic:

  18. Fit & Feminist have posted a relevant link today that claims that underweight people are at greater risk for dying than overweight:

    “Adults who are underweight — with a BMI of less than 18.5 — have a 1.8 times higher risk of dying than those with a “normal” BMI of 18.5 to 24.9, the study found.

    By comparison, people classed as obese (a BMI of 30 to 34.9) were 1.2 times more likely to die during a minimum five years of follow-up than normal weight people.

    The risk of dying was 1.3 times higher for the severely obese — those with a BMI of 35 or more.”

    Adding this information to the Edmonton scale, it seems maybe we should be focusing more on general healthy habits (exercise, food choices, stress reduction) and less on BMI.

  19. I certainly agree that we should be focusing more on healthy habits than BMI – but there’s a danger in inferring so specifically from that study! Lots of reasons why people are underweight don’t have anything to do with healthy habits they can cultivate in the future. For instance, many terminal illness cause underweight, some mental illnesses do, etc. In these cases, it’s clearly not the underweight, specifically, that’s leading to death.

  20. As has been mentioned, there are reasons to believe that being overweight/obese is not, in fact, dangerous, unhealthy or a problem. An excellent resource to read about this is here:

    The articles posed there (i.e. not the blog posts) seem to be reputable, based on good evidence, and from a medical professional.

  21. Correction, when I said ‘not the blog posts’ I meant to say ‘not the forum posts’. Sorry for the confusion, and for cluttering up this comments section.

  22. Here’s a different take along the lines of some of the skeptical comments above:

    Almost all of the criticisms of the BMI (including those in this thread) have to do with the advice-side of its use. Only rarely is the experimental side called out. Do you really think all the massive health studies that the advice is based on is putting everyone under the calipers? Almost all of them use BMI or some similar metric — anything else would be too hard/expensive. (Many of those studies are, after all, based on self-reported surveys or medical records.)

    Given that fact, what basis does one have to call some folks with a high BMI “healthy”? Do we really have good statistics on how healthy it is to carry large amounts of extra muscle compared with most people? If the answer is supposed to be that we know that diet and exercise are important for health, it has the same problems. We “know” that from the same kinds of studies, and in any case bodybuilders and many athletes tend to have unusual diets.

    The most likely reason the picture above is so convincing is that she _looks_ so healthy. And the overweight look less so. There is enough independent evidence for the association of severe obesity with specific health problems to implicate it, but there is very little scientific basis to make an exception for people like the woman pictured. And as Kimberly’s data implies, there is very little basis for the hectoring many people get from their doctors to get their BMIs under 25. Some studies put the risk in the “overweight” range _lower_ than the “normal” range. That hectoring is mostly cultural bias laundered through barely significant experimental results.

  23. Such a huge debate around the lack of basic knowledge about the BMI as a tool. This is hilarious and terrifying at the same time. BMI consists on a number obtained form the relation of your height and weight. In not athletes BMI works, and should be used. However athletes have more muscle mass (specially body builders), and since muscle is HEAVIER than fat, athletes like this woman have higher weight. BMI isnt and individual capable of making a fair analysis. BMI is just a mathematical tool that should be interpeted by a professional, and the only thing that BMI sees in muscular people is increased weight (be it fat or muscle, it cant differentiate them). Fortunately for this woman, in this case the increased BMI means that she has been doing a good job while working out. And that nurse should be fired.

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