Where can a man who is two stone overweight be seen as skinny? America, of course, land of militant fatties. By David Aaronovitch
I don't know why I was so surprised. Hadn't I watched Roseanne? Wasn't I familiar with Oprah Winfrey's extraordinary accordion-like expansions and deflations? Weren't some of the guests on American people-shows a bit on the large side? Somehow, my mental image of physical America was conditioned by the babes of California, Jane Fonda work-out tapes and thirtysomething (for which I still pine). In my mind's eye, your average non-underclass American was fitness obsessed, sports active and health conscious.

Then, last month, I went to Florida and met Fat America for the first time. On the beaches where I had uncomfortably expected to encounter body fascism at its most self-conscious - washboard torsos, pecs, "cute buns", pneumatic thighs and contemptuous glances - I found myself exchanging greetings with uninhibited men-mountains instead. No athletic beach sports, no limber 40-year-olds in Ray-Bans and Speedo trunks excelling at volleyball, but rather the slow lumbering and gentle floundering of huge people. Their principal physical challenge - whose turn was it to tote the cool-box? It was a revelation.

And it was all on display. Unlike fat Britain, fat America does not wear baggy black thigh-length maternity smocks to the beach, or sit covered- up in a cafe adjacent to the sands, sadly contemplating the antics of the slim and perfect. The uniform of the "big" American appears to be a figure-hugging T-shirt and clinging Bermuda shorts. And whereas obesity in Britain seems to afflict the occasional unfortunate member of otherwise trim families, entire clans of Americans, encompassing several generations, will trundle together to the sea's edge like participants in an Attenborough film on sea lions. Montanans describe them as polyester mooses, apparently.

Since I could happily lose a couple of stone myself, my first reaction to all this fleshliness was one of pure pleasure. Whatever I ate, no matter how much I indulged, I could never become as fat as many of these folks. Who cares how many calories a strawberry daiquiri has? There was also the pleasant feeling that they were giving me the once over and telling each other: "See the skinny guy? I think he's English."

It was also a marvellous opportunity to examine what happens to different people's bodies when they become very, very fat. Human beings wear obesity in various ways. Some plump American men like to describe themselves as "bears", and that is indeed one type. They have large, bearded heads, mounted upon thick muscular necks which grow in turn from a thorax and abdomen of equal immensity. Protruding incongruously from their shorts, like the sticks in one of those bulbous chocolate-coated ice-cream lollies, are two skinny little legs. Overall, they are hugely fat, but not really flabby, having put in a decade or two of hard physical labour and even harder troughing and drinking.

Their wives and teenage daughters tend to be barrels. The fat-filled skin is pink and healthy and distributed so as to make no part of the body or legs stick out. Everything is vast - tum, thighs, ankles, wrists, fingers - with the chubbiness most of us lose when we're weaned. The bear family have got fat by slow, deliberate accretion over time, pizza by pizza, Coke by Coke. They move with confidence and surprising agility.

Then there are those whom fat has suddenly surprised. From behind jowls and chins peek the oddly sharpened features of smaller people somehow surrounded by alien bodies. They have the hands and feet (sometimes even the shoulders and thighs) of their adolescence. Once upon a time they were kinda normal. But one night, two tubs of Ben and Jerry's in front of the TV took them over the edge. Now their fat weighs heavily and visibly tires them.

Finally, there are those who only deposit fat in certain parts of the body, and who therefore carry it like luggage. The women have enormous breasts and bottoms, like wearing three heavy inflatable lifejackets. The men possess a kangaroo pouch (filled with several baby kangaroos) where their stomachs ought to be, or fatty breasts slung forward from their shoulders, quivering loosely when they move.

However they got there, they all lack that crucial ingredient that the very fat Briton nearly always has - shame. I never saw the Bear family sitting miserably at Michelbob's Ribs Restaurant toying with a salad. In every diner and cafe and mall we stopped in from the Everglades to Disney World, they carried groaning trays brazenly to their tables - steaks the size of a Panama hat, invariably accompanied by fries and baked beans and garlic bread and creamy coleslaw and Coke or beer, followed by Key lime pie, or fudge cheesecake, or Mississippi mud pie, or a slice of each.

The results are predictable - lots of premature deaths. One third of Americans are more than 20 per cent overweight, and that number has increased drastically in the past 15 years. Such obesity causes all the expected health problems - diabetes, heart problems, wear on muscles and joints and sexual dysfunction. All of this is, of course, as well known to most fat Americans as the risks of drunk-driving or unprotected sex are over here.

So why do they do it? In all likelihood, some of them, looking at their compatriots, do not believe they are particularly fat. "Roseanne's fatter'n me and everybody thinks she's very attractive" is the siren song that the fat body sings to its owner. Besides, you can taste the artificial sweetener in Diet Pepsi. If you only approach mirrors from certain angles, refuse to take the camera on vacation and shop in specialist shops, you can forget your size for whole days at a time.

But many more are now questioning whether thin is better. They are fat and proud of it. Their movement - the fat acceptance movement (branches in all major towns) - advises which airlines are "big-friendly" (ie, will let you occupy two seats for the price of one), which cinemas will allow you to watch the movie from your own specially imported chair, and put you in touch with outfitters catering for the vast.

The movement has its own erotic literature, heroes and villains - and victims. For just as feminism - rightly - defined itself partly in terms of the victims of patriarchy (battered wives, witches, etc) and gay liberation through the homosexuals who suffered at the hands of the Nazis and the queer-bashers, so fat-acceptance activists (less credibly) can parade their own damaged heroes - Weight Loss Surgery Survivors. These were happy fat folks, destabilised by sizeism and Vogue ads, and persuaded into undergoing liposuction at the hands of unscrupulous quacks.

If the movement takes off and fat is thought of as beautiful, its easy attainment can only mean that Americans will get larger. Perhaps this is no surprise. After all, this is the country where the 332lb President Taft (1908-1912), after having to be rescued from the White House bath where he had become wedged, drew the inescapable conclusion that a bigger bath was needed.