I think there are some very interesting parallels to be drawn from fat politics to queer politics to lots of areas, and linking across and back again and all around. But I'm not particularly setting out to do that here. It's more like: this is the basic stuff that I find myself wanting people to know about when they say to me, almost as an aside, not sounding very happy,
"... And I really need to lose some weight as well".
The funny thing about it is that most people, when they hear this stuff, go "Oh yeah!". Most of it isn't exactly new or obscure. But sometimes it seems to be new for people to consider it in relation to their own lives.
So here we go for a quick tour...
Weight, size and fitness are different things
Being thin is not the same as being healthy. You can be thin and unfit, and you can be much fatter than is fashionable and still be fitter than a lot of people.
Being thinner is also not the same as being lighter. Muscle weighs more than fat, so if you get in training, you can simultaneously get thinner and gain weight.
For most people, weight won't be a useful measure of fitness, because your fitness can vary so greatly while you stay the same weight. It makes much more sense to measure your fitness directly (in some common sense way like timing a familiar walk at a comfortable speed, or noticing what it takes to get you out of breath) than to suppose that your weight or size tells you how fit you are.
Exercise and the legacy of school
Lots of people (of all sizes) have had a crap time doing compulsory competitive sport at school and they never want to do anything like that again. So a lot of people (of all sizes) are limited in their enjoyment of exercise by, for instance, wanting to avoid situations where people might laugh at them, or where they might be conspicuous, or where they don't think they'd be very good at what they were doing.
So there are cultural discouragements to anyone over average size (as well as to a lot of other people) in finding enjoyable ways to exercise. Or, to put it another way, it's perfectly possible physically to be fat and get fit, it's just that parts of it may be accompanied by people staring at you and being rude. This is a social/cultural problem, not a physical one. (More on this under "Conspicuous difference", below.)
Health versus fashion
People talk about the health risks of being over your "ideal weight range". But lots of people have a healthy weight that still includes an unfashionable amount of fat. For those people to lose weight would contribute nothing to their health - but that doesn't stop people saying or implying that it would. Our culture gets fashion mixed up with health.
Health and weight: Who says?
Even if you read on a chart that you're outside the theoretical "healthy weight range" for your height, it ain't necessarily so. That depends on who drew the chart and how they did their research. The statistics of at least some of the original charts have been criticised. I don't know the details but the gist of it is that the research was slanted (as has happened often in the history of science) by people's existing prejudices. Too much opinion, not enough genuine science.
And what if you are?
Even when people are sufficiently fat to be statistically more at risk for some health problems, there are still a couple of other factors to consider.
Firstly, being fatter makes you less susceptible to some problems. For instance, fat women are evidently at a lower risk for osteoporosis than thin women.
Secondly and more importantly, weight swings (such as those caused by so-called "slimming" diets) are evidently worse for your health than simply staying fat.
You hear a lot about the risks of being fat and you don't hear a lot about the risks of weight swings. Why? Maybe because people have been brought up to think negatively about fat, and because the diet industry doesn't want you to know about the health risks of weight swings.
The limits of statistics
It's not that I think the idea of connections between health and weight is completely irrational. I'm just saying it's over-rated.
Likewise, the idea of a range of weights that would be optimally healthy for a particular person makes sense. Just don't add more meaning to that whole thing than it deserves.
Remember what those charts are actually saying. They're based on research of things like: Of however-many people in a certain category, a certain proportion had a certain result. (For instance, of so many women in such and such a weight bracket, x number later had a heart attack.) On the other hand, the rest of the people in that category didn't have that result.
What the chart doesn't even try to illustrate is why some of them did and some of them didn't. And that's 'cause nobody knows in that much detail! Because people are very very complex beings and your health and future doesn't only depend on your weight!
In other words, the chart may be a clue, but it actually doesn't tell you what your personal ideal range of weights is (even if the research was as well done as possible, which is a separate question).
So, if you feel great, don't let a chart tell you there's a problem, and conversely, if you feel like you could use some exercise, don't let a chart tell you not to...
Of course, some people are naturally very thin. And some of them (the ones who are also particularly tall) are the people who get to be catwalk models in today's fashion industry.
(Some of the models probably aren't naturally that thin - there's pressure on them too to be thinner than they naturally are, by whatever means available, not necessarily healthy.)
If someone with the genes for being skinny does get fat, it may be correlated for them with bad health. But what may be above-optimal weight or size for a thin-genes person may be normal and healthy for someone else.
The diet industry's agenda
Lots and lots of companies make a profit on people's fat-phobia. Just look at how many products you can buy that use it as part of their selling technique. For some products, it's the whole point of their existence. If everyone were happy with their weight and shape, those companies' profits would go down.
Almost all magazines have to have advertising to survive - the less money they take from advertising, the more expensive they are to buy. The advertisers include the diet industry. Those advertisers are not going to be happy if all the readers suddenly start liking their bodies exactly as they are.
So, you might from time to time see the odd article on the joy and power of loving your body as it is, or the health risks of weight swings caused by calorie counting diets. But where the diet industry holds sway, those messages are always going to be more than balanced out by the subtle and not-so-subtle messages they'd like you to believe: "of course" everyone wants to be thinner than they already are, and "of course" you want to "get rid of" those "unsightly" curves, and "of course" cream cakes are "naughty".
With all this around us, it's an accomplishment for someone in this culture even to think about saying to themself "I like my body the way it is".
Although women have traditionally been thought of as paying a lot of attention to their appearance, and men less so, there are prejudices for men too. Like women, men aren't supposed to be "too fat" - but they also aren't supposed to be skinny. Cultural prejudice dictates that they "should" be muscly and tall.
Some people reckon the pressures on men are increasing. For the industries based around bodily appearance, men are an untapped market compared to women, and companies are going to want to take advantage of that. It does seem as though more and more adverts nowadays feature half-naked muscly male models, picked for their conformity to a stereotype that most men can never look like.
Any group of people about which mainstream culture is uneasy is more likely to get hassled in public than the average person: for instance, powerful independent women, people of particular races (varying from country to country), queer people, fat people and anyone whose body or abilities are unusual. While some differences aren't visibly obvious (e.g. you can be gay and closeted), some are.
One of the ways that phenomenon manifests in the case of fat people is that a lot of people think it's their business to tell the person how to live: particularly around food and exercise. For instance, people over a certain size get hassle (or simply what a friend of mine calls "The Look") if they eat in public. Some people seem to think that a fat person's life is public property. Even people only minimally above fashionable skinniness may well have comments from their friends "for their own good" about how they "could do with losing a few pounds".
(One parallel: the common experience of bi people being told "for their own good" that they ought to "make up their minds" or "sort themselves out".)
More on politics
Keep women busy worrying about their appearance, and they won't have time for politics
Fat represents being "out of control", so it's threatening to people who are trying to have everything/everyone under control
In a competitive environment, people feel superficially better when there's someone else to look down on. If fat people are characterised negatively, then however many people are looking down on you, if you're skinny you can still look down on fat people.
I read a lot of books written for children, and it's rare to find any character depicted as fat who isn't also depicted in some other way that's obviously considered immoral or unfortunate. For instance, it's said or implied that they are stupid or wicked or lacking in self-control. You're far more likely to read "fat and lazy" or "fat and cruel" than you are to read "fat and gifted" or "fat and beautiful". And on the rare occasions when a fat character isn't represented as somehow less than acceptable, then it's quite likely that their success or popularity is "despite" their "misfortune" of being so fat, or it's their one human weakness or whatever. The more you look for the subtexts the subtler ones you can catch.
(There are exceptions in children's literature - mostly written in the last 10 to 20 years by people who were explicitly conscious of what I'm talking about.)
So the theme is much more deeply woven into our culture than just "Here's a magazine article about how to lose weight, here's a bunch of models and they're all thin" etc.
It's funny how the word "diet", which used to mean something like "what you typically eat", now often means "eating less than you want or need". (Its root is a Greek word meaning "mode of living".)
The average Western diet has been designed more for convenience and habit than for health, so most people could think of at least one or two changes that would be healthier for them. Eating a big breakfast is good for some (most?) people - stoking up first thing means they'll have more energy all day. Choosing unprocessed foods, and switching to organic veg if you can afford it (or grow it), means more vitamins. The so-called experts don't all agree with each other, but you can investigate for yourself what foods and what eating patterns work for you. (Which foods give you energy and which send you to sleep? Which give you a quick boost in the first few minutes but then send you to sleep? If you currently have any health problems, how do they respond to different foods?)
Dieting by counting calories is different from choosing foods for health, and it frequently leaves people neither healthier nor in the end any thinner. The thing is, if you start eating less than you need, your body thinks there's a famine going on, and it responds by a metabolism change so that you can store more fat. This is why most supposedly "slimming" diets only work for a short time, and it's one of the things the diet industry would like to draw a veil over. It's quite handy for them that "slimming" diets usually don't work - it keeps people coming back for more. It's even handier when people blame themselves rather than blaming the whole idea of eating less than you need in the first place. "I need more willpower" - not!
"You'll never pull / get laid / find a partner looking like that"
One of the most prevalent, bizarre and unconvincing myths is the idea that you have to be thin to attract sexual partners. Who came up with that one???!!! There have always been both men and women who (all other things being equal) prefer to be with someone voluptuous / cuddly / ample. And that's aside from the obvious fact that people pick their partners based on a lot more than their body size and shape.
But, of course, this is a brilliant bit of manipulation - so much so that it's used virtually everywhere in the advertising industry. "This will make you more attractive to sexual partners" is the perennial implicit or explicit message, usable to sell almost any product you could imagine.
Being seen with the fashionable people
This is not to deny that some people are genuinely so prejudiced against fat people that they wouldn't even consider going out with someone over fashionable thinness. One of the dynamics that can be at play there is the way people sometimes use their partner to "prove something about themselves". To varying degrees (and probably almost always to some degree), people pick their partners based on what it would "prove" about them to be seen with that person, rather than based on the relationship between the two people. The more need people have for a fashionable partner in order to be comfortable in the world, the less choice they have about partners.
In many social situations it would be considered rude to use the word "fat" about someone. But activists have reclaimed it for bold and unashamed use.
An "extra layer" is "extra" only to some notional amount of fat that would be acceptable.
"Out of shape" and "getting into shape" imply a particular shape (only one) that the person ought to be and isn't.