Saturday, October 3, 2009

BMI and Stupid Assumptions

Excessive exercise often accompanies eating disorders. You wouldn't think it would be necessary to point out that this is not healthy, but as the ED Bites blog says, it's often hard for people to grasp that exercise isn't automatically nor universally a healthy behaviour.

A few weeks ago, we had a seminar with a case study (an invented case) about a woman with a BMI of 20. The medical students presenting this case described this as a "normal, healthy BMI" and then recommended that she increase her exercise as part of a list of general recommendations for improving health. The seminar leader, Dr. P, a family physician who had written these cases as composites from real scenarios, did not disagree.

A friend of mine with background in eating disorders work did say to the group that a BMI of 20 is very often neither normal nor healthy. Any woman presenting to her family doctor with a BMI of 20 deserves a screening for eating disordered behaviours rather than a blanket recommendation to increase exercise.

Another case during the seminar described a patient with a BMI of 32. At one point there was a list of behaviours that were affecting his health. Obesity was listed. I pointed out to the group that obesity is not, in fact, a behaviour. Then, as the case continued, Dr. P said that the individual's obesity would limit his ability to do his job as a construction worker. I asked why, and was told that he would not be fit enough to do his job. Dr. P did not seem to buy the argument that fitness is not the same as obesity.

The whole thing was incredibly irritating. Note that we're talking about a BMI of 32 here. In fact, every obese person described in the seminar had a BMI of 32 or 33. Apparently people larger than that are too unbelievably enormous to even consider... Thanks to Dee for the photo below, an example of a man with a BMI of 32.

Edited to Add: A number of commenters objected to my statement above about a BMI of 20 triggering screening for an eating disorder. That is not the same as assuming this patient has an eating disorder. She probably doesn't. However, given that anorexia nervosa is a relatively prevalent (0.5 to 1% prevalence means all family practitioners will see several cases) and very severe illness, I do think that every woman with a BMI on the low or low-normal side deserves a screen for eating-disordered behaviours. Screening in this case would be a minute or two spent asking questions about weight loss, amenorrhea, eating patterns, and exercise patterns.

Similarly, I screen everybody with a sleep complaint for major depression, and anybody who has had a traumatic event for PTSD. The vast majority of patients won't have depression or PTSD. But if 1/100 has a good chance of it then these are serious enough risks that I think screening is warranted. One problem with eating disorders is that it's really difficult to find prevalence rates and the studies vary widely about how common these illnesses are. I'd rather err on the side of screening too many people than miss one.

An additional issue here, unique to eating disorders, is that physicians do a pretty poor job of identifying patients until they get really, really sick. Knowing that there's a good chance I am already missing a lot of patients with these illnesses tends to lower my threshold for screening for them.


Anonymous said...

Ha! 32 and 33? Geez. I have a BMI of 40-something... My doctor struggles to find things wrong with me, even when she plops me down on a tredmill.

If 32 and 33 is as big as they're willing to imagine, seeing me would send them into fits. HAHA! Oh, the laughs I could have!

-Lexie Di

La di Da said...

Oh the lolz. This man: (Wendell Sailor, a professional Rugby League and former Rugby Union player)
has a BMI of between 30 and 32, depending on which player profile you read. Obviously he will have difficulty with any physical job.

Perhaps someone should make a flip chart of various people with various BMIs showing the different kinds of shapes and sizes you can be with the same BMI. Kind of like an analogue version of the BMI Project, because it's easier to whip out at moments like that.

Also it is obvious these people have never paid attention to the men and women working on construction sites (classism at work?). I can see one out of my office window and there are a couple of chubby-looking women, some wiry little guys, medium size guys, tall skinny guys, fat guys, one very fat guy, and all of them appear to be doing their jobs with no problem.

Ashley said...

The thing is, every person is different. No one should assume things when it comes to BMI. No one should assume a BMI of 20 is either healthy or unhealthy, same with a BMI of 32. Hell, mines is 17 and I am one of the healthiest people my doctor has known of. Then again, I know people with my same BMI that aren't so healthy.

With exercise, it's good when you do it in a healthy way. Of course, over working your body can have negative effects, but you also don't want to sit at your computer all day eating potato chips. Being active is a good thing, you just have to find a balance of that and rest.

Frankincensy said...

I'm quite surprised that a BMI of 20 would ring alarm bells unless there were other factors pointing towards disordered eating. It reminded me of the posts I've seen about doctors who immediately assume fat patients must be overeating and/or not doing any exercise; if those people deserve not to have their weight pathologised, doesn't the same go for people in the low-"normal" range?

Sarah said...

People with a low BMI have higher mortality rates than those with a high BMI, and have a harder time recovering from disease - a low BMI weakens the immune system.

Usually, a low BMI is a sign of malnutrition or a mental disorder like anorexia.

Ashley said...

People have eating disorders at any and every BMI. I hope I'm misunderstand some of the insutuions I'm picking up here, because a BMI of 20 alone certainly is NOT a "sign" of ANY sort of eating disorder or indication of malnutrition.

Robin said...

Every time I go to the doctor, he or she asks me how much exercise I'm getting. It seems to me that basic screening for someone who is already getting compulsive or overdoing exercise should be done for EVERYONE, regardless of BMI. Size is irrelevant as to whether moderate exercise is good and compulsive exercise is bad for a person.

As for the examples in question, there are people for whom a BMI of 20 is normal and healthy and people for whom a BMI of 32 is.

deeleigh said...

That's really shockingly ignorant. I'd say that a 32 BMI would be fairly typical for a construction worker (those would be the fit people with the large builds), and that a BMI of 40 would not necessarily be a disadvantage.

When I was doing building inspection work, climbing 40 ft ladders onto sloped roofs and then walking around on them, checking the flashings and penetrations; climbing ladders onto flat roofs, hauling up the ladders, and then using them to get onto higher roof levels; spending entire days on my feet, walking around and up and down multiple flights of stairs in large buildings, my BMI was around 34 - and I'm a woman.

deeleigh said...

Joy - show your instructor this picture:

That's my ex at 6'-0" tall and 245 pounds: a BMI of 33. Too fat to do construction work? The guy had a 36" waist and could carry me around in his arms. He used to carry 4 pieces of drywall at the same time. Most "normal weight" people aren't nearly strong enough to do the heavy work in construction.

Anonymous said...

Why is a BMI of 32 as unhealthy considered a "stupid assumption" but someone like me (BMI=19, eat like a pig and regretfully rarely exercise) should be screened because it is some sort of an anorexia warning sign? That would really offend me. If you saw me on the street, I would look perfectly "normal", not thin or fat or whatever. You must realize that there are people out there with BMIs of 30 and above who are eating disordered and their bodies just refuse to accept that because they are not SUPPOSED to be thinner...I am all about HAES, have a bf who is fat but eats better than I do and is just genetically different, but either BMI is crap or not- it should apply to both ends of the spectrum...


chartreuse said...

The idea of screening offends you that much? This is screening of the form "Is your period regular? Has your weight been stable in the past year? Do you have any concerns about your weight?" You seriously would be offended by a physician asking you that?

In short visits, we don't have the luxury of screening every person for every illness. So, we look at risk factors, and make sure that we screen out the most serious illnesses that a person is at risk for.

Anonymous said...

But shouldn't every woman be asked those questions? Thin and fat women alike have all sorts of period issues, weight fluctuations, etc. I just don't think anyone should be singled out.


chartreuse said...

Jill -- in an annual physical (usually 30 minutes booked) I often ask women those questions. Most appointments, though, are 10 minutes with multiple issues to deal with. So we always have limited time and there are virtually an unlimited number of diseases to screen for and questions to ask.

Medicine is all about stratifying what questions are asked, what tests are run, and so on, based on risk factors and severity of disease. There is nothing that we screen for universally.

When a mother comes in and tells me she's worried that her three year old is hitting himself when he is frustrated, I do a screen for autism even though the vast majority of the time this is a normal behaviour. Having a low BMI is a particular risk factor for dangerous eating disorders, so you bet I'm going to ask about it.

Look, if I screen 1000 women with a BMI of 25-30 for dangerous eating disordered behaviours, vs screening 1000 women with a BMI of 20 or below for dangerous eating disordered behaviours, I am going to get more hits in the low-weight group. It's a higher yield question in that group. (Here I'm talking about eating disordered behaviours that have immediate metabolic consequences, the kind that would be technically defined as eating disorders in the DSM.)

Frankincensy said...

Your ETA makes it clearer to me; thank you. I fully agree with not waiting to identify and treat people until the problem is severe.

familyfeedingdynamics said...

Great summary! Your voice needs to be heard in these lectures. I was a family physician and did not hear one word about HAES in my training. A BMI of 20 should trigger screening. A BMI of <19 can be an indication for hospitalization. How very frustrating for you! I work now in training medical professionals about appropriate feeding and growth, but we have a LONG way to go, and I think things seem to be getting worse before they will get better.

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Allen said...
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Anonymous said...

I do have to say that as a woman who has generally had a BMI of around 21, I have been quite offended by doctors in the past who have asked me a series of "screening" questions about my weight (e.g. "Do you eat breakfast every day?" "How often do you skip meals?"). I think that it's important for people to realize that it's also not ok to single people out for having a low BMI. Furthermore, the "normal" range of BMI extends from 18.5-24.9. If a doctor is expected to screen people with BMIs of 20 or below for malnutrition/eating disorders, should everyone with a BMI of 23.5 or above be screened for pre-obesity related eating disorders? It's quite strange to me for people place such importance on raising awareness about the inaccuracy of BMI in predicting health levels in people with higher BMIs, but yet to advocate flagging people with lower (but purportedly normal) BMIs as being at risk for eating disorders or malnutrition.

On a more social rather than medical level, I can't count the number of times I've been sitting with female friends, and the conversation has turned to the cozy topic of "bonding through being heavy", which inevitably leads to the comments about "skinny bitches", or the personalized comments about "man, you're so skinny!" or "you barely weigh anything! you're just skin and bones!". In general, I think people need to realize that it's really never ok to introduce someone else's weight as a topic of conversation, whether you think that person is overweight or underweight. I don't really enjoy hearing people talk about how "skinny" I am (which I think it frankly silly, since I'm a perfectly normal weight), and I can't imagine I'd enjoy the conversation any more if I were heavier and people were substituting the word "fat" for "skinny".

lahorton said...

I want to give you my dieting story...this is only one of the times I lost weight - I have done it several times now!

I started Weight Watchers, for like the 900th time, in 1998 at 345 pounds (you know the BMI is through the roof at this point). I lost 152 pounds (over the course of 3 years) and made it down to 193 at which time my weight loss came to a screeching halt. Now, I’m a 5′7″ woman and my “ideal” weight is around 135-140. So, I had a good bit to go.

So, for the next two years following the 152 pound loss, I continued with WW, cut my points down and kicked up the exercise to the point that I wore all the cartilege out of both of my knees (I now have double knee replacements). My weight didn’t budge below 193 no matter what I did!!

Guess what folks – wait for it, it’s good!!!! ALL OF THE WEIGHT I LOST CAME BACK (plus a little more at this point)!!!!!! Talk about wanting to jump off a cliff! You would think that weight wouldn't have come back. I thought I had it licked after 5 years!

I absolutely refuse to go back on a diet of any kind. I am striving to eat intuitively and give my poor body a break.

I have dieted and exercised for the past 40+ years and I am fatter now than ever. What does this tell you, research gurus? Let me answer the utmost of scientific questions for you……dieting doesn’t work and, in fact, eventually makes you fatter! Doesn’t take a genius to figure that one out. Check your statistics on how many people manage to maintain a weight loss.

Now my doctors are trying medications - I have had EXTREME reactions to Metformin and Byetta. Yes, I'm one of the 0.00005% who gained weight on Byetta. Go figure!

I've been told that if the weight doesn't come off...I will die of a heart attack. This was told to me by a doctor who has never listened to my heart.

Tell me medical what point are we "allowed" to accept ourselves for what we are? We are destroying ourselves trying to fit the "norm." Not everyone fits the norm!!

Tallahassee, FL

unscrambled said...

How did you make it through four years? I'm just finishing my first, and ready to do something unpleasant to 60% of the students and half the faculty. gah.

Good luck, wherever you matched! I hope we'll hear from you in residency!

Cat said...

I really appreciate what you said about it being preferable to screen a woman with a BMI of 20 for an eating disorder. I would definitely agree with this. I have a BMI of 20 and the vast majority of people think "I look great", but my body is not meant to be this size. I face alot of discrimination from medical professionals who think my problem is not "serious" enough to warrant help because I am not technically underweight and my eating habits (after a decade of battling this) have somewhat stabilized enough to keep me safe.

It's very frustrating. I think it really comes down to the belief tha anyone with a BMI between 18.5 and 25 "must" be "healthy", which as most of us know on sites like this, IS TOTAL CRAP.

So, that in mind, thank you for your advocacy and activism promoting people to accept HAES. Brilliant concept, it's facilitated a fundamental shift in my recovery and willingness to gain weight and give a giant middle finger to anyone who thinks I shouldn't.

Asin said...

I am afraid if I was screened for an eating disorder by my physician, it would not be a recommendation to go back! If making judgements on people's health based on overweight/obesity is wrong, it's just as wrong to judge someone cause you can't imagine being as light as them.

And yes I have a BMI of 20, have had my weight remain within a 5kg range for 15 years, and have a dad who still wears size small clothes and parents who encouraged me to be active from a young age.

Naomi said...

I like your comprehensive view on fitness/obesity. The BMI is flawed and there are indications that these flaws are quite serious!

BTW. Not sure if you already know this but the next DSM (used by Psychologists, Psychiatrists) will classify Obesity as a disorder.

Chris Serong said...

I'm a guy and my BMI is 30. I lift a lot of weights, and am one of the strongest people I know. I'm also not thin, and I'm a perfect example of someone who could do really well as a construction worker, from a physical fitness point of view. It's a frustrating thing, that people seem to think your weight reflects your athletic capacity. My weight has just as much bearing on how much I like the colour blue.

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