Is the "Obesity Epidemic" a fantasy?

[brynndragon]

One of the things I noticed when examining the requirements for the study I'll be participating in is the BMI cutoff is 27. Which seems strange because the BMI cutoff for "overweight" is 25. Apparently it *was* 27 until 1998 when the National Heart, Lung, and Blood Institute (NHLBI) decided to make it 25. I can't for the life of me figure out why they made that decision. They state, "The rationale behind these definitions is based on epidemiological data that show increases in mortality with BMIs above 25 kg/m2." with several references. But only one of the references implies that lowering the cutoff might be beneficial (the one that states "available evidence suggests that minimum mortality occurs at relative weights at least 10% below the US average", where the average according to this article (referenced in other places in that NHLBI document) is right around BMI = 25 for women and somewhat above that for men - which makes me wonder why the hell they picked 25). All the rest use overweight = 27 as their basis for making statements about the link between overweight/obesity and morbidity, except the WHO report (PDF). The WHO report doesn't say a damn thing about links between obesity and morbidity/mortality (being focused on malnutrition), nor does it give any specific recommendations at all about where to set BMI even for determination of malnutrition (for which it has good reasons involving the risk of overlooking important aspects of the link between height/weight/age and morbidity/mortality, and translating it into useful intervention, which the NHBLI seems to have completely ignored).

The thing I really want to point out is almost all of the data they use to support the notion that being overweight leads to increased morbidity/mortality involves a BMI >27, not a BMI >25. This might explain why the study I'm participating in uses the 27 cutoff rather than the 25 cutoff.

I probably only care because my BMI is 26. Well, that and the idea that over half of Americans are overweight is based almost entire on this change for which I've found pretty much no freaking evidence. The more I learn, the more dubious I am of our notions of healthy weight. . .

Comments

This is my burning ball of fury

[metahacker.livejournal.com]

1. BMI absolutely sucks as a diagnostic tool. It turns a cubed-relation into a squared-relation, is based on no experimental data, and ignores frame completely.

We might just as well say you should weigh 2 lbs per inch of height -- it literally makes as much sense, but because it doesn't have a square root in it it doesn't sound sciencey.

2. There is a rampant level of obesity in this country. Travel west of NY or south of DC to see it. The north east is pretty skinny.

3. Using BMI is making it hard to study the problem of obesity. How I loathe that measure.

Re: This is my burning ball of fury

[digitalsidhe.livejournal.com]

I was also going to post a comment to the effect that I can't understand why in the world anyone (aside from possibly quack "diet and fitness gurus" who are trying to push a particular agenda) is still using BMI. It's obviously a pretty worthless measure; it makes the average muscular athlete with 3% body fat look just as "overweight" as someone who's mostly flab.

But I think your points 1 and 3 do a better job than anything I was going to say.

Re: This is my burning ball of fury

[rigel.livejournal.com]

I ask out of genuine curiosity, not to contradict you or metahacker . . .

. . . do you have a better measure to suggest?

I agree with your point about BMI, actually.

Re: This is my burning ball of fury

[heinleinfan.livejournal.com]

Just for sake of discussion, and not to hijack a question directed at someone else, who could probably answer it better...I'm just rambly today...

I think that a major problem with "a better measure" is tied into our whole screwed up healthcare and health insurance system. A better measure would be a *full* measure of an individual's overall health, as opposed to an arbitrarily defined "Here's your label" type of measure. But things are too screwed up to offer most people that level of individualized health care, you know?

Re: This is my burning ball of fury

[metahacker.livejournal.com]

This is also an excellent point. "Here, have a number that says you are a bad person and will die early. Now leave, minus $120."

Re: This is my burning ball of fury

[brewergnome.livejournal.com]

It's hard, because you need a health measure, and then an actual fat measure, which to do properly requires a full body MRI to see where fat is getting deposited (skinny people can be fat if all their little fat is deposited around organs).

Re: This is my burning ball of fury

[benndragon.livejournal.com]

Which is why the people doing the study need 5-6 hours for a physical exam ;P. I wonder if I'll get a copy of that analysis that I can give to my doctor, just for his edification. . .

Re: This is my burning ball of fury

[brewergnome.livejournal.com]

THAT would be awesome.

Re: This is my burning ball of fury

[metahacker.livejournal.com]

One of the problems is one of the old "why are you looking near the lamppost for your lost keys?" "That's where the light is!" variety -- the things that are easier to measure get used because they're easier, not because they are accurate. (For BMI, everyone knows their height and weight and they are easy to get from corpses for mortality data)

When people talk about obesity they are generally talking about excess fat. There is some concern with overweight-ness from internal organs getting physically bigger, but I haven't heard one way or the other whether that is good, bad, or indifferent. There is some evidence that having extra muscle makes the heart work harder, but our society doesn't seem to care. Likewise extreme calorie restriction may greatly lengthen life, so having any body weight at all may be a liability, but few seem willing to eat the right 800 calories every day, and those guys may be wrong anyway.

Body fat percentage is harder to measure, but probably better for addressing the kind of obesity people are really concerned with. Ideally you'd get a full body composition breakdown, but I don't know how to measure that.

When I was a kid there was software that came with calipers and asked you to measure bits of yourself, and produced a reasonably accurate body fat % number. There are some scales that claim to do it based on some sort of electric current thing. And measuring your density (float you in a tub of water to get your volume, then divide) somehow gets to that number too, though I don't know how they differentiate bone vs. muscle vs. other internals. Google...

But the real kicker is that there's the question of 'is all excess fat bad' and 'is some excess fat (e.g. fat around organs vs. skin-layer fat) worse than others' and 'what is bad' anyway. I think we're all clear on the idea that having 50+ lbs of fat is probably obese, but what does that actually mean for health? This is what was implied in my #3. We don't know, and our classification schemes are making it hard to find out, because we lump together mortality of all people who are some weight X at some height X^2 * C.

Re: This is my burning ball of fury

[digitalsidhe.livejournal.com]

You beat me to it, and did it better, again. Thanks. I was basically going to suggest body fat percentage, and note that unfortunately, it's not as easy to measure as height and weight.

Re: This is my burning ball of fury

[heinleinfan.livejournal.com]

Somewhat related...my current burning ball of fury is nutrition in general and how food relates to the environment...which is, in many ways, tied to obesity.

We (we as in humans in general and especially americans) just *don't eat right at all* and we don't eat right because we've been listening too long to people who not only aren't looking for their keys in the right places, but are also being told by people who have a vested interest in keeping them under the light poles to look in those wrong places.

Like...nabisco has started replacing trans-fats with non-transfats in their stuff, so suddenly "Fritos corn chips" can have a label slapped on them saying they're heart healthy! The hell they're healthy, not for humans and not for the planet. But nabisco paid some scientists to do a study on transfats, and the scientists duly reported that yes, if Fritos had nontransfats instead, they'd be healthier!

GAH!

Re: This is my burning ball of fury

[plymouth.livejournal.com]

It turns a cubed-relation into a squared-relation

So, not that I think BMI is all that and a bag of chips, but a squared relation DOES actually make sense - when people gain weight they generally do it in two dimensions (they expand sideways and forwards/backwards) so you don't have to consider those dimensions as separate variables. Yes, I know, it's not monotonic and people will gain in different places first - butt, thighs, gut, whatever - but it all averages out to being the same in both horizontal dimensions, both of which are significantly smaller than the vertical dimension until we get to really extreme obesity.

Re: This is my burning ball of fury

[benndragon.livejournal.com]

Actually, there is a use for the BMI in the doctor's office. It should function as an initial observation indicating a need for further examination as part of a preventative strategy and/or possible avenues of exploration for the source of signs & symptoms if someone is already experiencing health problems. However, it seems to be treated as an if-then statement (if patient BMI exceeds $foo, then patient needs to lose weight; if patient BMI is less than $bar, then patient needs to gain weight) rather than a single clinical manifestation that is meaningless without context. But if a doctor is unlikely to realize it is merely an indicator that further examination is necessary, how the hell can a layman be expect to figure that out?

I'm not sure what the solution to this problem is. Replacing the BMI with some other measurement won't address it.