I'm still thinking about fat. The intense responses to the idea of fat acceptance are often justified in terms of health. The more I think about this, the more, intertwined reasons there are for calling bullshit on it.
Firstly, there's the science. All the research on obesity. Lots and lots of it is sponsored by the diet industry. Oddly, this doesn't seem to bother the medicos citing it. Also, more transparently, the premise of obesity research is to treat obese people as a uniform group of people. To look at obese people and compare them with not obese people. In many respects, health outcomes are worse for obese people. However, as well all know, correlation is not causation. Just as the strong correlation between the population of storks and number of babies born in Hamburg fails as evidence against babies being born via their mamas' vaginas, this correlation on its own doesn't mean obesity is the root cause of all evils.
I'm completely down with diet and lifestyle being correlated with good health - in fact I also believe that it is partially causative. (Many people know perfectly well that their ill-health has nothing whatever to do with diet and lifestyle, so it can't be more than a partial causation.) Also, because weight loss is sold as the goal for everything, and the marker of health, there is a correlation between obesity and poor diet and lifestyle. The direction of causation is not so clear though. Once you are fat, if eating healthy and exercising sensibly don't produce weight loss, why would you bother? It's clearly not working anyway, since weight is health. I can't help wondering if body fat was ignored completely by everyone, how much healthier many fat people would be. Still, here I am focussing on fat people. Just like the research. No-one seems to round up all the people with similar diet and lifestyle, irrespective of weight, and look at health outcomes. Plenty of not fat people have crappy lifestyles and crappy health outcomes, but no-one glares at them when they eat in public. So I call bullshit on fat = unhealthy.
Also, the only lifestyle that's really been looked at independent of the starting weight of the people is the Dieting lifestyle. (I use big D "Diet" to refer to weight loss regimes, rather than the stuff you eat.) That's been shown to be really bad for you - with increased risk of stroke and heart disease. It's really bad for you, because it produces yo-yo weight gain and loss, and that's definitely worse than constantly being fat or thin. So I call bullshit on being told to go on a Diet for health reasons.
Moving on to practical matters. The public shaming of fat people causes bad health. It stops fat people going to the doctor, because they know they're just going to be told that whatever is wrong with them is because they are fat. They are far less likely to have preventative health checks, because they know the doctor is going to tell them they're fat (in case they'd managed to forget this fact for a millisecond). It means that doctors treat people with less respect, and with less actual medicine, as it happens. 95% of people can't lose weight and keep it off, so doctors prescribing that as a cure-all is simply bad practice. So I call bullshit on the idea that making people feel bad about being fat will lead them to be healthier.
From the practical to the moral. Who said healthy was the be all and end all to all arguments anyway? Everyone has the right to decide what priority they want to assign to what degree of health. Apparently one is a hard working moral citizen if one gets a stress induced illness (even if the source of stress is a result of choosing high income over low stress occupations) but totally devoid of morals if one chooses to focus on other aspects of lifestyle at the expense of one's health. Sports people are allowed to destroy their joints requiring surgery and more, and are hailed as heroes. I call bullshit on lack of health being viewed as a moral failing.
Finally, I've heard more than one person point out that the upside of cancer (or other life threatening illnesses) is weight loss. I can't think of better evidence that the claim that fat hatred is all about health is utter, utter bullshit.
And when I say "fat people" as though they are other, it's because I'm an in-betweeny. I'm well and truly obese by medical definitions, but I can still sometimes buy clothes in mainstream shops. So some of the fat hatred (and all the body shame) come my way, but I realise I don't cop it as bad as lots of other people.
Also, if you want to change your diet (with a little "d") to improve your health or make other lifestyle changes because they make you feel better, that's cool. If you lose weight as a result, that's also cool. If you don't lose weight as a result, that's exactly as good as if you do. For a fabulous piece on how talking about Diets affects other people, have a read of this Spilt Milk article.