Jeffrey M. Friedman is my fat science hero!
There’s this argument I reference quite a bit about humans naturally coming in a range of shapes and sizes because of genetic diversity. It’s my “weight distribution curve” argument.
I first learned about the weight distribution curve when I read this post on JunkFoodScience.com: Obesity statisticulation — When will people get it?
Even before I got into FA, I was aware that statistics can be manipulative. And I’m certainly not immune to it. If I stare too long at the CDC statistics saying that in 1980 the obesity rate was 15% and now it’s up to 27% I’ll have a flash of FA doubt.
The argument made by the JFS post says if you plot BMI by population, the SHAPE of the weight distribution curve hasn’t really changed over time. It’s just shifted over a bit.
I really like that argument and I use it a lot, but I have to admit there’s always been a little doubt at the back of my brain that one day I’m going to learn some new concept about statistics that would show me the flaw in that argument.
It’s important to me that I don’t just parrot information. I want to make sure that what I’m saying has a sound basis. But I’m not trained as a statistician. I’m doing my very best to understand epidemiological concepts, but there is always the chance that I’m missing some part of the big picture.
So, this week we’ve been talking about the HHMI 2004 Holiday Lectures about Obesity. I’m watching Lecture 1, Deconstructing Obesity, by Jeffrey M. Friedman, M.D., Ph.D. and it comes to the part where he says,
…there’s a known phenomenon in in epidemiology when you have a fixed threshold for a trait, a small shift in the average value has a disproportionate effect on the number of people who exceed the threshold.
And I felt a sense of relief wash over me. It brings two concepts together: how it can be that the shape of the weight distribution curve hasn’t changed that much over time but the rate of obesity has has doubled.
The funny part? In the original JFS article — the one that informed me about the weight distribution curve—heavily featured quotes from an NPR interview of Jeffrey M. Friedman.
Of the four lectures about obesity, the first one was my favorite. I think Jeffrey M. Friedman totally kicks ass. He explains the complex issue of weight clearly and in a way that made sense to me. His lecture reaffirmed stuff I already knew and taught me some new stuff, too!
Thanks for that … I am slightly creeped out by your timing though - last night I randomly dreamed that I was looking for information on this! o_O
You were destined to find Fierce, Freethinking Fatties. Welcome and I hope the creepiness subsides soon.
Peace,
Shannon
Excellent post! I’m going to post a link to it over at Fatties United!
Thanks Whaliam. And welcome!
Peace,
Shannon
Thanks! (But the link to the JFS post doesn’t work.)
Vidya -
Fixed the link.
I’m not sure why there would be any shape change in a normal distribution. I have a very elementary understanding of stats, but I thought the basic bell curve was going to stay the same for any variable with a normal distribution. No matter what mean BMI is for any population, wouldn’t we expect a bell curve graph for the population as a whole?
Also, I can’t tell for sure, but it looks like on the graph comparing data from NHANES, the standard deviation may have increased with each study. AFAIK, that means that the number of people on the outer edges of the curve have increased. I thought that might match up with data that I know I’ve heard before that, rather than average weight increasing, we’re seeing a lot more people in the ‘extreme’ edges of the weight category.
I really wish I could magic myself back in time to those talks. I have soooo many questions I’d like to ask.
attrice -
The reason I use the argument is to correct the misunderstanding that weight is increasing in a straight line. Informing people that there IS a normal distribution to weight and even if you can say the fattest people are getting fatter, you also have to be aware that there are thin people staying thin and other people throughout that range who are not changing weight at all.
Although the CDC took it down, I remember seeing the report that said the people who gained the most weight were already in the overweight/obese category. (25lbs as compared to 10lbs) I’m endlessly frustrated that I didn’t capture that page before they took it down.
I totally agree with the statement that naturally fat people are genetically different than naturally thin people and that’s part of my personal argument for fat acceptance. At the very same time, I feel the information being handed to the public about fat is blown out of proportion. We still have people on all points on the spectrum, as is shown by the fact that the shape of the curve hasn’t changed that much.
And, yeah, I also wish I could ask some questions. Like the comment about how saying the weight of the population has changed means it isn’t genetics is a misunderstanding of evolution. I would love an explanation of that one.
Also, I’d love to know WHERE he got the proof saying that the urge to eat works in a “3-9 month” timeframe. That’s an awesome piece of information but I don’t want to fall prey to a fallacy of authority, since he’s the only one I’ve heard that info from.
“The reason I use the argument is to correct the misunderstanding that weight is increasing in a straight line. ”
I’m not sure what you mean here. I agree that people aren’t aware of the fact that weight is normally distributed - although most people don’t really know anything about stats so it’s not surprising. Are you saying that the graphs above can show how small the average shift in weight has been even if the % of people in the obese categories has gone up a lot - rather than the ‘everyone is gaining weight and will one day be 40 bajillion pounds!!!!!’ stuff?
I only want to clarify because depending how one was looking at it, weight is also linearly increasing for the population as a whole (if we’re talking averages) even if that line is a lot less steep than the average person probably believes.
Really, I agree with you. I think I have more issues with the way JFS is phrasing some things. That’s pretty much par for the course though.
Yeah, that phrase about genetics caught my attention too. I’m trying to convince my friend who is doing his PhD on…well, I don’t want to get too specific b/c it’s not a common area of research…but it has to do with epigenetics to write a post explaining some of the basics (he is great at making this stuff accessible) but he’s pretty hesitant.
attrice -
The argument is aimed at the “average person” and to help the burgeoning activist disassemble “‘everyone is gaining weight and will one day be 40 bajillion pounds!!!!!’ stuff”
Dr. Jeffery Friedman IS an absolutel genius. I have the greatest respect for the man. Morboid obesity is hellishly complex and the unknowns are far greater than any known. The stigmatization of obese people si nto scientifically supported at all.
Great blog you have here and I am VERY happy to see you choose reputable world renowned sources of information. This is VERY rare. Kudos to you !
The Internet is full of people who are clueless about obesity. They are seeling people their nonsense etc.
Take care,
Raz