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[personal profile] sarahmichigan
The classic example of this is "When ice cream sales are high, so are murder rates. So ice cream consumption must cause murders." Of course, there's no causation there; ice cream sales and murder rates just both happen to go up when the weather is hot. Other examples can be found here:

http://www.don-lindsay-archive.org/skeptic/arguments.html#correlation

There are a lot of arguments about the dangers of obesity that rely on this fallacy. People assume that because there's some (but not as much as we're lead to believe by the popular media) correlation between increasing weight and increasing incidents of certain diseases and premature death that obesity causes these diseases and premature death. But when you factor out certain lifestyle elements, such as activity, consumption of fruit and vegetables, and smoking, the picture becomes more complicated. It's more likely that lack of activity and poor eating habits both contribute to obesity and to ill health, not that obesity causes ill health in and of itself, since people who are obese but who exercise regularly have virtually the same life expectancy as thinner, active people.

This fallacy has also mislead some people to be anti-vaccination because of the supposed correlation between exposure to mercury in vaccines and the rising rates of autism. As more children have been vaccinated, the argument goes, more cases of autism have occurred. Therefore, the mercury in vaccines must be causing autism. There are no well done studies that show any link between the mercury in vaccines and autism. What is more likely going on is that over the years, screening is catching more cases of autism in children AND the criteria for diagnosing mild forms of autism have broadened, resulting in larger numbers of children being diagnosed as autistic, not necessarily that there are many, many more causes of autism occurring than in previous years.

On the other hand, you can't entirely ignore strong correlations in medical studies; this is exactly how we found out that tobacco smoking causes cancer. The strong correlative evidence between cigarette smoking an rates of cancer is something like *900 times stronger thank the link between obesity and most diseases it supposedly contributes to. And, we also understand something more about the mechanism of how tobacco smoking causes cancer, which lends additional evidence besides the correlative evidence to the smoking/cancer link.

* I remember the numbers being something close to that according to Glenn Gaesser in "Big Fat Lies" but I don't have the actual number in front of me. Post to be updated with exact number when I can track it down.

Date: 2007-02-07 12:13 pm (UTC)
From: [identity profile] theal8r.livejournal.com
Hey -- do you happen to know -- what is the actual, scientific link between second-hand smoke and diseases? I hear things quoted all the time, but I've never *seen* one of these studies.

Date: 2007-02-07 02:30 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
My understanding is that the science supporting the dangers of second-hand smoke is a lot weaker than that supporting the link between smoking and cancer, but I haven't done enough research on the topic to give a really informed opinion.

Date: 2007-02-07 02:50 pm (UTC)
From: [identity profile] meecie.livejournal.com
Another reason people connect autism with vaccines, is that the onset of symptoms often correspond to the age children receive their first MMR vaccine. Child gets shot, shortly after, child develops fever, then shortly after that, child develops autism sympmtoms. That particular link, I'm pretty sure has been disproven, but it's *very* understandable why parents would think there was a causal relationship in those cases, even if it is a fallacy.

Date: 2007-02-07 03:28 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
Oh, right! I had forgotten about the timing issue as well.

Date: 2007-02-07 03:28 pm (UTC)
From: [identity profile] riffalike.livejournal.com
Supposedly this fallacy was the reason behind the design of the chart of global temperature versus number of pirates: http://en.wikipedia.org/wiki/Image:Pchart.jpg

Date: 2007-02-07 05:58 pm (UTC)
From: [identity profile] stacycat69.livejournal.com
Spurious correlation! My big sociology word of the day.

The obesity stuff, you have to both filter out lifestyle issues (such as food and exercise) but you also have to filter out the effects of weight cycling. Do you know any fat women who have never lost and regained weight? :-) they are even coming out with new studies that show that people who are losing weight have higher risks of dying than those that stayed at the higher weights.

Date: 2007-02-07 06:03 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
Yes, I think weight-cycling is really dangerous. It's not the losing weight so much as the regain that seems to raise blood pressure and fat-to-muscle ratios and so on. Since 90-95 percent of dieters regain, repeated weight-loss dieting is a recipe for wrecking your metabolism.

"Correlation does not imply cause."

Date: 2007-02-07 05:58 pm (UTC)
From: [identity profile] http://users.livejournal.com/_earthshine_/
This is a huge one for me. I often half-jokingly like to expand it to "Correlation almost never implies cause" because of how often i feel it's abused.

Constructing a truly bulletproof empirical study is actually really really hard. The number of possible variables wherein external causation can be hiding is often prohibitively huge, and even if one can miraculously find them all, finding a population that diversifies over all of them to allow for statistically significant results is a monumental task in and of itself.

Scientific efforts are absolutely important, and need to continue, and need to be very carefully conducted and documented for reasons like this. And, in the end, we must also remember that they are exactly that: efforts. I think the cases where a single empirical study can pop out and truly make a significant dent in human understanding are few and far between. Moreso, it's the slow and gradual contribution that these things make over time that progresses the state of our awareness along. While it's admittedly very inconvenient, i think a healthy outlook for us to keep as a very general baseline is that the progression of knowledge from prospective hypothesis to accepted fact requires something on the order of decades. There are certainly wide variances/exceptions to this, but i believe we're best off judging things very conservatively as a rule of thumb.

Date: 2007-02-07 06:51 pm (UTC)
From: [identity profile] guttaperk.livejournal.com
The relationship between obesity and illness is not as simple a causative line as many doctors may claim for reasons of speed/simplicity or ignorance; but neither is it as distant as many would like to believe for reasons of personal comfort or consolation.

Obesity is a marker of risk. It's an imperfect marker, but it is a marker.

If the risk is being addressed via diet/exercise/general good healthcare, then we should move on.

If not, then we shouldn't.



It goes without saying that the absence of obesity in no way indicates an absence of risk.

Date: 2007-02-07 07:11 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
Obesity is also protective against several kinds of diseases, and weight-cycling is certainly dangerous to your health. So picking out obesity as a stronger risk marker than any other risk factor and trying to address it rather than lifestyle choices is counter-productive, in my opinion.

Date: 2007-02-07 07:52 pm (UTC)
From: [identity profile] guttaperk.livejournal.com
Be careful.

I don't think it's particularly true that "obesity is protective against several kinds of diseases". It's more accurate to say that "obesity will delay the effects of many kinds of wasting processes". If you get terminal cancer, obesity will delay your death. The same benefits accrue from being muscular, with less fat.

There are a few diseases of women against which obesity is protective; but the risk of death and harm from cardiovascular disease greatly outweighs these protective benefits if diet & lifestyle issues are not addressed.

Weight-cycling is utterly, utterly dangerous- but that fact does not refute anything that I have said.

Nor do most people "pick out obesity as a stronger risk factor than any other risk factor"- most people will still pick out strong family history, smoking, history of major concurrent illness such as diabetes and hypertension, etc., etc. to be more important than mild to moderate obesity.

Be careful that you do not take the low-lying outliers as representing standard of practise. The truth is not to be found in the shrill proclaimers of either the obesity-haters or the obesity-defenders. It's somewhere in the rational middle.

For what it's worth, obesity is the focus of Yet Another Stupid Cultural War in America. I'd hate to be even mildly plump in the U.S- things are much more measured here in the Caribbean. Plus-size people in America have reason to be defensive, in my opinion.

It still doesn't help, though.

Date: 2007-02-07 08:12 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
-Obesity protects pre-menopausal women from breast cancer.
-Obese people suffer hip fractures far less often, and hip fractures are a huge risk factor for premature death.
-People who are obese at the time they're admitted to the hospital for heart failure are 2.5 times LESS likely to die than those who are not obese when they're admitted.
-Obesity has been publicly linked with cancer, but an overview of various kinds of cancers finds that obesity is only linked with increased incidences of a very few kinds of cancers, and for many cancers, there is NO link between obesity and increased risk, and for certain cancers, the fatter you are, the LESS likely you are to develop that kind of cancer.

Date: 2007-02-07 10:29 pm (UTC)
From: [identity profile] guttaperk.livejournal.com
You've made far too many points for me to properly respond to all without being more argumentative than even I am willing to be.

Many of the studies you cite come down to this: if you're going to be weak and ill, it's better to be weak and ill with padding and energy reserves.

It's still better, overall, to be non-weak, non-ill, and non-obese.

Please note that by "obese", I have never been referring to cosmetic obsessions with five or ten (or fifteen) pounds, or with normal middle-aged body profiles.

In one of your comments, you attributed several views as possible views of mine. I have espoused none. I meant what I said, and nothing further.

Neither did I say, or mean to imply, that *you* in particular were being defensive. Before, anyway. I do think that now. But, as I said, Anglo-American folks do have lots of reasons for defensiveness.

Do you recommend that tall males get sex changes and get several inches of bones removed from their legs so their shorter? No, of course not. But that's exactly what doctors are doing when they tell patients to cut calories and lose X amount of pounds rather than addressing lifestyle choices that are much more easily addressed than losing X amount of pounds and keeping them off permanently.

I half-agree with you.
I agree in that I routinely correct doctors who focus too much on pounds and not enough on methods. When I've given people advice, I tell them to focus on how their body feels most of all; to weigh, if they do at all, not more than once a month; and to recognise that short-term weight loss or gain is a very poor indicator of health. I tell them that part of their goal should be to build muscle, and that since muscle is better than fat, that they may not actually lose much weight.

I disagree with your current tack in that most people who engage in any vaguely medically acceptable means of losing pounds and inches, even if they focus on such things excessively, will also generally be making positive lifestyle changes; the same is not at all true (as far as I know) for your rather melodramatic analogy.


I'm sorry if it seems to you like I'm nitpicking. I'm trying to keep the big picture in mind. In closing, I want to state that my basic position is, as I said, that the truth is in the rational middle; and if I say that some people are defensive, I also acknowledge that they are under attack.

cheers

adrian.

Date: 2007-02-08 01:15 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
You seem to be implying that my position is somehow extreme, and I don't think it is, at all, especially not the few sentences I included in my original post.

I do feel HIGHLY condescended to by your comments on this thread. I can give a list as long as my arm to back up everything I said in my original post and every claim I've made in the comments. Don't come onto my journal and pat the poor, defensive fat girl on the head and tell her how sympathetic you are unless you're looking for an argument.

Date: 2007-02-08 09:21 pm (UTC)
From: [identity profile] guttaperk.livejournal.com
I did not mean to offend you. I did not think of or refer to you in that fashion- as a "poor, defensive fat girl".

I think that misunderstanding would be reduced if you ignored what you took as implications of my statements. All of the things that you have noted thus far as implications are things that I did not say, and don't agree with.

I do regret any offensive implications received.

Adios!

Date: 2007-02-08 01:36 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
Many of the studies you cite come down to this: if you're going to be weak and ill, it's better to be weak and ill with padding and energy reserves.

It's still better, overall, to be non-weak, non-ill, and non-obese.


Some, but not all come down to that. It's probably the fat itself that is protective in some cases, and a similar weight in muscle is NOT as protective. For instance, it is probably something about the way fat stores hormones that makes being obese protective against breast cancer for pre-menopausal women. And studies about putting on weight below the waist being protective against heart disease clearly show that people with more FAT on the thigh, and NOT more muscle, that corresponds with protection against heart disease.

Date: 2007-02-08 09:25 pm (UTC)
From: [identity profile] guttaperk.livejournal.com
Sarah, that's why I said "many" and not "all". :-)

Date: 2007-02-07 08:19 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
-As for cancer, a 2003 report on a 16-year study of 900,000 American adults found significantly increased death rates for several kinds of tumors among overweight or mildly obese people. Most of these apparently obesity-related cancers are very rare, however, killing at most a few dozen people a year for every 100,000 study participants. Among women with a high BMI, both colon cancer and postmenopausal breast cancer risks were slightly elevated; for overweight and obese men, colon and prostate cancer presented the most common increased risks. *For both women and men, though, being overweight or obese seemed to confer significant protection against lung cancer, which is by far the most commonly lethal malignancy. That relation held even after the effects of smoking were subtracted.*

-http://content.nejm.org/cgi/content/short/348/17/1625

In this study, the authors do find a SMALL increased mortality rate for *some* kind of cancers for extremely high BMIs (40+) but there is a list of at least a half a dozen different kind of cancers where there was absolutely no link between BMI and mortality rates. Furthermore, people in the "overweight but not obese" category actually had a decreased risk of cancer over people in the "ideal" weight group. But that wasn't reported. The study's authors lumped in the numbers for the overweight and the extremely obese and averaged them out. If you look at the numbers carefully, being a little overweight by government standards in terms of cancer prevention is better than being at your so-called "ideal" BMI.

Date: 2007-02-07 08:28 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
Oh yes, and obesity is protective against osteoporosis, as well.

The link between obesity and heart disease isn't particularly strong if you factor in activity level. Autopsies on fat people haven't found that they don't necessarily have more occluded arteries than thinner people; much of the risk here is hereditary, part of it is food choices (sat fats vs. non-sat fats), and lack of activity.

Again, my main point I think you mostly agree with. Obesity isn't, in and of itself, particuarly indicative of any kind of increased risk. Bad diets and lack of activity are the big risk factors, independent of BMI.

Date: 2007-02-07 08:35 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
-obesity also appears to confer some protection against prostate cancer, particularly in men older than 60.
-higher BMIs are associated with better survival rates for those with chronic kidney disease.

Date: 2007-02-07 09:07 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
You know, I'm not even sure how we got off on this tangent. When I'm at the doctor, I do get defensive about weight issues. In this post, I was not being defensive-- I'm just telling the truth. You seem to have issues with this paragraph:

There are a lot of arguments about the dangers of obesity that rely on this fallacy. People assume that because there's some (but not as much as we're lead to believe by the popular media) correlation between increasing weight and increasing incidents of certain diseases and premature death that obesity causes these diseases and premature death. But when you factor out certain lifestyle elements, such as activity, consumption of fruit and vegetables, and smoking, the picture becomes more complicated. It's more likely that lack of activity and poor eating habits both contribute to obesity and to ill health, not that obesity causes ill health in and of itself, since people who are obese but who exercise regularly have virtually the same life expectancy as thinner, active people.

What part of that paragraph do you have a problem with? The fact that obese people who are active have better mortality rates than thin, sedentary people and about the same mortality rate as thin, active people? The fact that being at the high end of your "ideal" BMI or the low end of "overweight" is better for mortality than being on the low end of your so-called "ideal" BMI? The fact that the correlation between even very high levels of obesity (greater than 40) and most diseases is very weak?

Date: 2007-02-07 09:22 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
I'm also mildly offended by the implication that I'm bringing up confusion about correlation and causation and the obesity wars because of "personal comfort or consolation" and that I am being defensive.

I wasn't feeling particularly defensive until you started to challenge me. I think it's clearly true that much of the "evidence" that obesity is dangerous to your health is correlative and that much of the correlation goes away when you adjust for other factors (such as weight cycling and activity levels).

I can have a vested interest in believing that the links between obesity and ill health are very weak and inconclusive and STILL BE RIGHT based on the facts. You don't want to do forensic jujitsu with me on this topic unless you have your facts VERY straight because I have done a shit-ton of research on this topic.

Date: 2007-02-07 09:58 pm (UTC)
From: [identity profile] http://users.livejournal.com/_earthshine_/
Frankly... what's not to believe here, anyway?

If you truly boil out correlative issues -- like links between unhealthy diets and obesity, or between unhealthily low activity levels and obesity -- then we're effectively comparing two people with identical direct health metrics (whatever they may be -- activity, blood chemistry, whatever).

In such a comparison, it seems intuitive to me that -- all other metrics being equal -- the person with (a) greater energy reserves, and (b) better genetic/dietary resiliance to body fat in general would naturally be better off for both contracting and fighting off some diseases. Again, all other things being equal, it makes perfect sense to me that a person with higher body fat would be far better off in most cases.

I think what limits the applicability of this tho to (sadly) only the few folks who are very educated on the topic is the fact that "all other things being equal" is perhaps the exception and not the rule for most Americans. Many people probably just (wrongfully) assume that obesity is the indicator of some other health problem; that may be true more often than not, but the point is that people (including some doctors) don't realize that it's not always true.


For completeness, my understanding is that there are a few diseases where greater body fat simply makes the disease more risky just from a body-chemistry standpoint -- but my source is only secondary and may be part of the biased world. Diabetes is the example i've heard about; something about higher body fat making sugar levels harder to regulate simply for chemical reasons, all other things being equal. Does that match your research?

Date: 2007-02-08 12:04 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
There was an article not too recently with a headline something like "Verdict on Fat and Fit mixed" or something like that, because two studies had come out about the same time, one saying that fat people who got regular exercise had about the same heart health as thinner folks, but then another article saying that weight control was better than just exercise with no weight loss for controlling diabetes.

However, I know of other studies done where obese folks were put on a food and exercise plan and improved their insulin sensitivity without losing very much or any weight; in one study, average weight loss was on the order of 5-6 pounds and some didn't lose any weight at all, but all improved blood pressure, insulin sensitivity, and other measures of health.

The one health condition I think there's a fairly good reason to believe that it IS causation rather than correlation is in joint issues; more weight on the joints, more joint problems. However, since overweight people often have, for instance, arthritis in the wrists as well, it doesn't seem like 100 percent can be blamed on the weight, either.

Date: 2007-02-08 02:47 pm (UTC)
From: [identity profile] http://users.livejournal.com/_earthshine_/
OK... so it sounds like more research is needed on the diabetes issues, but that (unsurprisingly) diet and exercise matter far more than body fat, which doesn't surprise me.

The joint-issue point is a good one, but it also has to do with weight, which can also just be a person's size or musculature, right? Muscle is heavy, too... though maybe in the muscle case, the joints are more supported (by the muscle) so it evens out?

Interesting stuff. The end points seems to persist: it's best to use better metrics than size/shape/weight to determine health and/or diagnose problems; after that, your body will probably be healthiest being left at whatever size/shape/weight falls out of pursuit of those healthy metrics, and if that resultant shape includes some fat reserves, you will have some advantages against some diseases (and perhaps disadvantages with few others, but that's not certain). Nothing about that seems counter-intuitive to me.

Date: 2007-02-08 12:47 am (UTC)
From: [identity profile] guttaperk.livejournal.com
Seriously.

Forget what you think I implied, or what you think I seem to disagree with.

Do you have a problem with what I actually *said*?

Date: 2007-02-08 01:50 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
Yes. I disagree with you on a variety of points.

Date: 2007-02-08 02:01 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
-The relationship between obesity and illness is not as simple a causative line as many doctors may claim for reasons of speed/simplicity or ignorance; but neither is it as distant as many would like to believe for reasons of personal comfort or consolation.

I disagree. I think most of our evidence about the "dangers" of obesity are confusing correlation and causation.

-I don't think it's particularly true that "obesity is protective against several kinds of diseases".

I disagree. I've given several examples where FAT ITSELF is protective.

-There are a few diseases of women against which obesity is protective; but the risk of death and harm from cardiovascular disease greatly outweighs these protective benefits if diet & lifestyle issues are not addressed.

With the caveat of "if diet and lifestyle issues are not addressed," I partly agree with you. With that left off, I completely disagree. Even with the caveat, I disagree that there are only "a few dieases of women" where fat is protective. Obesity in and of itself is not a particularly strong predicdtor of heart disease.

-Be careful that you do not take the low-lying outliers as representing standard of practise. The truth is not to be found in the shrill proclaimers of either the obesity-haters or the obesity-defenders. It's somewhere in the rational middle.

I disagree with you that my position, especially as stated in the original post, is extreme or irrational.

-Many of the studies you cite come down to this: if you're going to be weak and ill, it's better to be weak and ill with padding and energy reserves. It's still better, overall, to be non-weak, non-ill, and non-obese.

I disagree with this, too.

-I disagree with your current tack in that most people who engage in any vaguely medically acceptable means of losing pounds and inches, even if they focus on such things excessively, will also generally be making positive lifestyle changes;

I disagree here, too. Most dieters regain the weight, and we know that weight-cycling is dangerous, and the "positive lifestyle changes" that accompany most weight-loss dieting are short-lived for the vast majority.

Date: 2007-02-08 09:36 pm (UTC)
From: [identity profile] guttaperk.livejournal.com
I have neither time nor interest in a battle with you, which is the way that this is going.

You have vastly misunderstood both content and intent of my comments. I'm not going to fight that at this point.

If you're interested in an exchange of ideas at any point, I'm game.Right now, it looks like you're more interested in proving me wrong.

It so happens that many of the ideas that you're proving wrong are nothing to do with what I am saying.

I've never insulted or demeaned you. I've never called you fat. I did not recommend unsustainable changes or short term diets. I never said that your position was extreme or irrational.

Finish your argument with whoever holds those views, because it ain't me. If you have gotten that idea from my comments, you have misunderstood, and clearly my further comments have not been successful in reducing that misunderstanding.


No hard feelings. It happens. We're all flawed human beings. I accept that I've played my own role in (accidentally) fanning the flames of misunderstanding.


cheers

adrian.

Date: 2007-02-07 08:38 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
I see what you're saying about the difference between protection from "getting" a diseases and improved outcomes for those who already have the disease, but obesity is actually protective against some diseases AND it provides better chances of surviving other diseases and conditions if you DO get them.

Date: 2007-02-07 08:51 pm (UTC)
From: [identity profile] sarahmichigan.livejournal.com
Being tall and being male are also strong markers for risk. Do you recommend that tall males get sex changes and get several inches of bones removed from their legs so their shorter? No, of course not. But that's exactly what doctors are doing when they tell patients to cut calories and lose X amount of pounds rather than addressing lifestyle choices that are much more easily addressed than losing X amount of pounds and keeping them off permanently.

I think we probably agree on much of the big picture and we're just nit-picking details at this point.

Do I think that there's NO causation between BMI and health and mortality rates. No. Not at all. But I think there's only reason to worry at the extremes of underweight and extreme obesity. Even then, it's much more productive to focuse on diet and activity levels than on changing BMI.

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