On Tuesday I attended a lecture on campus, and as I walked into the room, a class had just ended and the professor (whom I know casually) was still packing up her stuff. I saw on the whiteboard some what looked like a list of reasons why people are fat. So I asked the professor what class it was and what they had been talking about, and she said it was a health psychology course and that today's lecture was about "weight". I mentioned that I had an interest in this subject and was curious about what they talked about, and she said they had discussed the conscientious objectors experiment (I assume she meant this) and she showed a CDC slideshow about the change in "obesity" rates in the US over time (scare quotes mine) (and I'm guessing it was this). In the most casual possible way, I asked what the slideshow did about the fact that the BMI cutoff for obesity was changed in 1998 (well, I actually said I wasn't sure, but it was in the 1990's and I thought 1996). She responded that the cutoff was 30 and had been 30 for a very long time and that she never heard of the change I was referring to. This I found kind of disturbing, since here she was lecturing students about BMI but didn't know the history of the BMI standards. Maybe it's a minor point, though. Anyway, what bothered me even more was that she went on to say about the CDC slideshow, "What's really striking about it is the change." And I was like, "The change?" and she was like, "Yeah, the increase in the percentage of obesity state-by-state over the years." And I said, "Hmm, I wonder how much of that is attributable to demographic changes," and she replied, "No, it can't possibly be explained by that because the change is way too dramatic." Since the lecture was about to start, I just smiled and said, "Hmm," and then added that I'd love to talk more about this stuff with her sometime, and she said that sounded good.
So I sat there during the lecture, totally unable to focus, instead just stewing about how the students at my institution are getting a misinformed view about fat. When I got back to my office, I wrote the following email:
It was interesting chatting with you this morning and I wish we'd had more time to talk! While I'm thinking of it, I just wanted to send you a link to a post on a blog that I read, where Paul Campos critiques the traditional view of BMI (I don't know if you're familiar with his work, but I could send you some references if you're interested). Here is the link: http://lefarkins.blogspot.com/2008/08/obesity-apocalypse.html. If you get a chance to look at it, I'd be curious to know your reaction to this line of argumentation. One of the most interesting points, to me, is the fact that the average weight has not actually gone up by a very large amount in the last 30 years (and I think it would be even less if you factored in the increased average height over the same period). So I wonder whether demographic trends actually could explain quite a bit of the change. I also think it is interesting to consider what other factors have contributed -- it sounds like you talked a bit about that in your class. I'd love to know if you have the students reading anything in particular about this that I might be able to get ahold of.
Also, I looked around online and found some references to the change in BMI standards. Apparently it happened in 1998, not 1996 as I thought. I forget what happened to the standard for "overweight," but the "obese" cutoff was a BMI of 32 prior to 1998 and then changed to 30. I don't know what the CDC materials do about this change -- I think I found the slide show you mentioned, and it just says "BMI >=30", implying that they applied the new standard to the data from all years including pre-1998. On the other hand, impressionistically it looks like there's a big jump between 1998 and 1999, so I wonder whether they could actually be applying the old standard to the data from 1998 and previous, and then just stating the modern cutoff. That would certainly be interesting to know! I also think it is interesting to think about what the motivation was for the cutoff being revised, and indeed for the cutoffs in general.
Anyway, I just thought I'd drop you a line about this, and if you are interested in talking more I would be glad to do so.
After I sent it I obsessed about how she would react to the email, because from the little that I know about her I actually like this person, and people around campus seem to respect her. And I kind of think if another professor sent me an email challenging something I had taught in class, I might get a little defensive about it no matter how nicely it was worded. So I forwarded my email to a colleague who knows her well (and who isn't necessarily a true believer in everything I think about fat, so I figured she'd be objective), and she said she thought it was "completely collegial". For the rest of the day on Tuesday I kept checking my email and wondering when she'd write back. But now that a couple of days have gone by, I've realized that the reaction is not actually the most important thing here. First of all, there's a chance I got the wrong impression and this person actually has a more enlightened view than I'm giving her credit for. I did see that one of the things on the list written on the board was "Genetics 50-60%" (I may have the numbers wrong, but it was something like that), so at least that was apparently acknowledged (though I think the actual figure is higher, to the extent you buy into these percentages that people try to assign to the role of genetics in X). But even if her views are actually quite yucky, at least I've given her a little taste of the idea that there exists a critique of the mainstream view. I wouldn't expect to suddenly change someone's mind with an email, but who knows, maybe next time she lectures on this stuff she'll at least say, "There are those who disagree..." and then perhaps a student will pick up on the comment and go out and learn about the alternative point of view for him/herself.