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A while back, I made a post related to weight loss dieting, and in the comments, [livejournal.com profile] shreena asked me why I do believe that politically and scientifically, health at every size and similar approaches are 'better' than weight loss dieting, commenting:
I'm interested in the evidence base on this. I have not looked into it so I don't really have an opinion but I'm interested by the fact that many intelligent knowledgeable friends of mine hold the view that you [...] have expressed but so many health institutions and guidance hold the opposite view (i.e. that health and size are correlated.)
I possibly shouldn't have shoved this in with the December Days prompts, because really I want to put in lots of links to evidence rather than just writing off the cuff as I end up doing when I'm trying to post every day. But equally, I don't want to duplicate the work that lots of other fat acceptance / HAES bloggers have done really comprehensively, so I'm going to try a brief run-down here, and follow up in the new year if this isn't satisfactory.

In order to address this prompt, I am going to talk about weight loss and dieting and also about the medical establishment's attitude to fatness and fat people. My plan is to take this post in a fairly sciencey way, given [livejournal.com profile] shreena asked for the evidence base. I have a political opinion, which is strongly body positive and against medical and other discrimination against fat people. But I'm going to try to be as neutral as I can, and I'm going to entertain various possible interpretations of the evidence that I'm discussing. I'm aiming to present a case to intelligent, open-minded skeptics, basically, and I appreciate that even acknowledging the possibility that fatness may cause bad health is going to be offensive or upsetting to some people.

Further, I'm talking purely about the connections between size and health. I am committed to the view that health is not a moral imperative, so even if I saw enough evidence to completely convince me that it's always healthier for everybody to be as thin as possible, I would still argue that people have the right to choose whether they want to go on weight loss diets or not. But that's not the point of this post, I want to explore the question of whether losing weight actually is beneficial to health.

I should also warn about the comment discussion that might come up. I didn't do so last time I discussed this topic, and some of the comments ended up upsetting some friends – I'm very sorry about that. I generally get a lot of pushback when I talk about this sort of topic, because some of my friends are more politically radical than me, and some are convinced by the orthodoxy about fat and health. I hope everybody will be civil and sensitive about discussing a fraught topic, but I expect a fair range of opinions here. I may also not have time to answer comments, partly because it's about to be Christmas and partly because I'm trying to keep up this daily posting for another couple of weeks, given it's been so satisfying up to now.

As I said, there's a lot of good stuff available examining the evidence for and against weight loss dieting for health, and I'm relying quite a lot on secondary and tertiary literature, I haven't personally examined every single study about weight loss ever published! Though I have read quite a lot of them, both several that support my view and several that do in fact show weight loss is good for health outcomes. I strongly recommend the blog Junkfood science which has absolutely masses of links, and basically anything by Paul Campos, who has a number of articles online but no centralized blog, but who has written a book, The obesity myth which goes over a lot of the relevant science as well as the reasons why the science is ignored or misinterpreted.

I think the thing that caused me to question the assumption that fat people should lose weight to become healthy was probably something like this ancient link round-up, which cites a number of peer-reviewed studies that come out against intentional weight loss and in favour of HAES. There have been, to my knowledge, several large, high-quality studies in the most recent decade that point in a similar direction. However there have also been a great many studies that show beneficial effects of weight loss, so I don't want to just cherry-pick the stuff that agrees with my beliefs. I want to talk in fairly general terms.

So, with that preamble, my first point is that health and size are correlated is not actually the "opposite" of health at every size and similar approaches are 'better' than weight loss dieting. There may in fact be a correlation between being fatter and having poor health outcomes, and there is indeed some evidence for such a correlation, though also some evidence against it, as I shall go on to discuss. But that doesn't at all imply that deliberately restricting calories in order to lose weight will make a currently-fat person healthier. Being fat may be correlated with ill health, without being the cause of it, in which case losing weight won't help. Being fat may be the cause of (some) ill health, but losing the extra weight may well not fix the damage potentially caused by being fat in the first place. Finally, losing weight may be good for (some) people, but, contrary to what naively seems expected, restricting calorie intake, ie what people normally mean by dieting, may not be a good way to achieve weight loss. In fact my knowledge of the research leads me to conclude that all of these maybes are in fact true.

Is fatness correlated with ill health? There are certainly some studies showing such a correlation. Particularly studies of people who already have a serious illness, such as heart disease or diabetes; in such groups, the fattest individuals tend to have the shortest life expectancies. There is also pretty sound evidence that really extreme obesity is correlated with poor health. However, in long term studies of the general population, there's more and more evidence that people classified as overweight live longer on average than people classified as "normal" weight, and even some evidence that people classified as obese, but towards the lower end of the range so classified, have the same or better life expectancies as people classified as normal weight. So at the very least the range of weights considered healthy or unhealthy are pretty dubiously evidenced.

Also, BMI, which is the easiest thing to measure and the most commonly used in studies of the health effects of obesity, is really not very well correlated with actual fatness; it is merely a ratio between weight and height, so it's affected by things like proportion of muscles and ethnicity and body type. Now, of course the answer to this is to use actually meaningful measures of fatness, such as body fat percentage, waist to hip ratio and so on, but a huge number of the studies that make claims about size and health in fact rely on the rather unscientific measurement of BMI, so you have to be careful in how you interpret them.

Further to this, there are at least some big, high quality studies which show that fatness stops being correlated with poor health if you correct for confounding factors. A big one is the Framingham study which is the absolute gold standard in risk factors for heart disease, since it's been following thousands of people for over 60 years. This shows that being overweight has little or no effect on heart disease risk if you correct for race and socioeconomic status and things like that. I mean, there's a strong correlation between being overweight and being poor; maybe it would do as much good to give people more money and resources as to deny them calories. There's this study which really shows that fatness is only an additional risk factor in people who also smoke and drink too much alcohol and do no exercise and don't eat any fresh fruit and vegetables.

But the problem with any statistical analysis that corrects for confounding factors like this is that you don't know that they're true confounders, they may in fact be relevant to the effect you're trying to use. Some people will dismiss the lack of effect of fatness alone seen in Framingham and similar results as irrelevant because there are very few individuals who are actually rich and healthy and have all these other advantages who are also very fat, even though the statistics predict that such people would be expected to be just as healthy as similarly advantaged thin people.

Correlations aside, I have seen very little direct evidence at all that losing weight improves health outcomes. And believe me, I've looked for it. It's usually just assumed that if fat people have worse health, then losing weight must improve health. But that doesn't follow at all; it seems actually quite likely that if being fat is bad for you at all, the damage caused by being fat is irreversible or at any rate poorly reversible. I've seen people trying to disappear the inconvenient result that the lower end of the supposedly overweight-obese range is correlated with longer lifespan by stating that the important factor is the highest weight people have ever been; some normal weight people may in fact have bad health because they were once fat and then lost the weight. Which is a plausible explanation but has never been proved either way, and if that is the case there's not a very good reason to encourage fat people to diet!

There is very mixed evidence about "weight cycling"; some studies purport to show that fluctuating weight, as you might see with someone who diets and then regains weight repeatedly, have worse health than people who remain at a constant weight, even if that weight is higher overall. On the other hand I have seen those studies hugely criticized, and many people who seem to know what they're talking about will vehemently deny that there is any harm associated with weight cycling. This is one issue I haven't really come to a conclusion about, I'm just telling you there are competing claims out there. And it seems at least plausible that big changes in weight may be as harmful or more harmful than having a high absolute weight, or indeed that dieting itself may be bad for some people.

Anyway, in summary, there is some evidence that high weight is correlated with poor health, especially very high weight. There is some evidence against this view too, but I'm reasonably prepared to believe there is sometimes a correlation there. But there is little evidence that losing weight improves health. So (in spite of my hardline political stance) I think it's probably medically worth it to try to maintain a lifestyle that prevents major weight gain, but once you are already fat, I am not at all convinced it's worth going on a diet to lose that weight. Or at least, if you want to be healthy, eating a balanced diet (without calorie restriction) and doing plenty of exercise have both been shown very clearly to have beneficial effects. Along with other things like getting enough sleep, drinking in moderation and not smoking at all and some mental health things that are a bit complicated to discuss here. Whereas the evidence for weight-loss dieting is extremely equivocal.

Which brings me to my third point. One of the major reasons there isn't clear evidence about whether weight loss actually helps is that successful weight loss is surprisingly rare. The huge majority of people who attempt to lose weight by dieting regain as much as they lost or more within a few years of stopping their diets. Fat activists claim that it's about 5% who lose weight and keep it off, but it's not very clear where that figure comes from. I mean, I've seen peer-reviewed studies of diet methods that claim a higher success rate than that, though my general impression is that they tend to be fairly short term.

But it's not unusual to see studies claiming that a method of losing weight is "successful" when the amount of weight loss is really tiny, like a few kg on average even after really intensive support and not counting all the study participants who gave up the diet before they'd completed it. Here's an example where the conclusion was that low-calorie, low-fat and low-carb diets are equally good, while what the numbers actually say is that fewer than 1 in 6 of the people who successfully stuck with their strict diets had lost 10% of their body weight and kept it off after 2 years (no matter which method they used). And, well, if someone was classified as obese or extremely obese when they started their diet, losing 10% of their body weight usually isn't going to put them even close to a so-called "normal" weight category. I haven't got links to hand but it's interesting that even bariatric surgery has a fairly high failure rate (like 30-50% IIRC, but that's not going to be convincing if I can't show you the cites); even among people who have had their stomach stapled or half their digestive tract removed, who therefore physically can't consume "too many" calories, many regain much of the weight they initially lose.

But again, I don't want to cherry-pick studies just because they support my view. I think one of the most interesting is the Look-AHEAD study, which is one of the biggest and most rigorous diabetes studies, which researchers halted because they weren't seeing any improvement in health outcomes based on their weight-loss interventions. And that's some pretty serious health intervention, the people in the study were getting way way way more support than your average dieter, even one who signs up for a guided programme like Weight Watchers or Slimming World or whatever. But the weird thing about that study is that they claimed that their interventions were "successful" in producing important long-term weight losses and improvements in cardiovascular disease risk factors among a significant proportion of severely obese individuals, but when you look at the numbers, it turns out what they're calling "important" is an average weight loss of 5% after 4 years, and with error bars of ±7-8%. That is, even the most intensive and best evidenced weight loss intervention you could ever imagine only helped people to lose about 5% of their body weight; if they were severely obese to start with they were still severely obese by the end. And, well, those error bars are bigger than the absolute average weight loss, which strongly suggests that some people gained weight. Now, that's people with type II diabetes, so it's possible that people who don't have diabetes are more easily able to lose weight. But still, it's kind of suggestive.

I find it very plausible that most people (not all, but most) have a natural set-point for their weight. The body has mechanisms to keep weight constant, even with increased calorie intake and decreased calorie output, or (as the typical situation of a dieter), restricted calorie intake and increased activity. It would make evolutionary sense to try to hold weight constant through fluctuating food availability, wouldn't it? And that's made more plausible by the cluster of studies that show very small changes in weight, or changes that are reversed as soon as the intense diet phase ends, even with quite drastic changes in calorie balance. Of course the set-point is not absolute, it seems to gradually creep up with age, and hormones and some drugs affect it. But there probably is some kind of homoeostatic mechanism in play there.

So, maybe weight loss would hypothetically be good for people's health, but for many people it's not actually possible. Not without really quite extreme measures, anyway; most commercially and even medically promoted weight loss diets are nowhere near enough to bring about long-term, large scale reductions in people's weight. So that means that people are putting lots and lots of effort into something that's extremely likely to fail, especially if the goal is to change from being very fat to being the medically approved "normal" weight. Whereas if people were to put the same amount of effort into improving their stamina and cardiovascular fitness and eating healthily and so on, they would probably get many if not all of the health benefits anyway, without having the extremely discouraging effect of not achieving their goal. Because outside of strictly controlled experimental studies, many many people give up their diets if they find they're not losing weight or they are regaining what they lost. So that's basically the HAES thing, people should try, or be supported if they're in a situation to get medical support, to actually live more healthily, without worrying about the number of kg they weigh. Especially since that number is only very dubiously connected to health and is also, for most people, pretty hard to change.

And my final reason for saying that HAES / weight neutral health initiatives are better is that insisting on weight loss does measurable harm. It makes people hate themselves, and people who hate themselves aren't very likely to alter their behaviour to be more healthy. It can also exacerbate eating disorders and other mental health problems. So even as far as it's true that health and size are correlated:
  • there is weak evidence that losing weight actually improves outcomes
  • losing weight is rather difficult to achieve, especially losing enough weight to change fat people into normal weight or thin people
  • weight loss diets and insisting on weight as a measure of health do actual harm

Does that help? Basically that's where I'm coming from on the issue, scientifically, though my political views do follow on from and extend that. I don't think it's going to be enough to help my brother and his housemate argue against the weight centric approach being applied to care home residents, but it's the best I can manage in an evening.

[December Days masterpost]
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