Kath Read, a size 26, has found pride and purpose via her website and blog, Fat Heffalump: Living With Fattitude. Credit:Paul Harris Then, six years ago, while perusing Twitter, she came across some links to fat liberation sites like Shapely Prose, Fatshionista and The Rotund. The sites were a revelation: they were funny, honest and subversive, and written by self-described "mouthy fat broads" who didn't feel the need to apologise for their body shape. "I spent a lot of time reading these sites and thinking fat liberation was a great concept, but that it wasn't for me, that I wasn't good enough to participate." But then she came across a photo on Tumblr of the Australian fat activist and performance artist Kelli Jean Drinkwater, and was "blown away ... Here was a fabulous woman with a body that looked like mine." Read is now one of Australia's foremost fat activists, with a website and a blog called Fat Heffalump: Living With Fattitude. The site, which gets 20,000 hits a month, is a zesty blend of self-empowerment and straight talking, a deceptively bubbly-looking forum where Reid riffs on everything from fat fashion ("fatshion") to the treatment of fat people by the medical profession, digressing only occasionally to deliver a good kneecapping to the odd troll. One of her most recent posts was in response to a 25-year-old guy called Matt, who emailed her to discuss how he genuinely wanted to be attracted to fat women, but how the sight of them "prevents me from having an erection". "Fat shaming is bad and counterproductive," Matt wrote. "This message is a personal thing, not a judgmental thing."

Faced with a lack of clothing for larger women, Erin Cox started the A-Plus Market in Melbourne. Credit:Thom Rigney Read responded with an open letter on her site: "Dear Matt, I couldn't give a flying f... about your boner. My value, and the value of other fat women on earth, is not measured by whether or not we give some random douchebag a boner." Attached to the post was an image of a T-shirt that read: "If I have not melted at least 10 boners a day, then I am not doing my job." Elyse Lithgow has a degree in nutrition and says there's more to good health than being the "correct" weight. Credit:Thom Rigney The fat acceptance movement has been around since at least June 1967, when New York radio personality Steve Post staged a "fat-in" in Central Park. According to Sports Illustrated magazine, 500 people turned up, some carrying banners reading "Fat Power" and "Buddha Was Fat", and wearing buttons with "Take a Fat Girl to Dinner" and "Cure Emaciation". Protesters burnt diet books and photos of Twiggy, and ate ice-cream – perhaps the first and only instance of a dessert becoming a political statement.

In 1969, an American engineer called Bill Fabrey, sick of the discrimination directed at his overweight wife, started the National Association to Advance Fat Acceptance. But progress was slow, and in 1973 a small group of women on the west coast of the US started the Fat Underground, a splinter cell that took its cues from the radical left, harassing weight-loss organisations and staging fiery speeches denouncing doctors and the diet industry for conducting "fat genocide". Being fat is very isolating. If you're a fat chick, you stay home, and that's not good for your mental health. The Fat Underground fizzled out, but fat pride powered on, becoming a bolshy brew of radical feminism, queer politics and body acceptance. (Most fat activists are women, thanks to the traditional emphasis placed on a woman's appearance.) Fat priders don't apologise, not for their circumference nor their defiance, and they don't mince words: "fat" is what they call themselves, and they prefer that you call them that, too. Indeed, many fat activists regard their battle for acceptance as akin to the civil rights movement, or the struggle for gay and lesbian equality. In Australia, fat acceptance has established a rowdy beachhead on social media and the net – collectively known as the fat-o-sphere – which has in turn spawned plenty of real world fat action. There are now fat studies conferences, fat reading groups, fat yoga, fat swimming clubs (like Chunky Dunk in Melbourne), and fat dance, including the excellently named Va Va Boombah, a fat burlesque group in Melbourne. But one of the most active expressions of fat pride is in fashion. "Wearing clothes is a necessity, but there are rules about how fat women are meant to dress," says Erin Cox, a 35-year-old bioscientist who works at La Trobe University in Melbourne. "They're meant to wear dark colours and cover their bodies so they're not seen, and that can be very depressing."

Two years ago, when Cox was pregnant, she walked into Target looking for a sports bra. "The biggest size they had was 12, and I'm a 20. It just made me really angry. The message was that I was meant to be exercising, but when I went to get a sports bra, I couldn't, so the message then became: 'Go home and sit on the couch and rot, we don't want you in our society.' " And so, in 2013, Cox started the A-Plus Market, a quarterly fashion sale held in an arts centre in Preston. A-Plus, which I visited in November, is not like other markets, and not only because the labels have names like Hey Fatty and Curvy Couture. It has the air of a secret society, a safe haven where plump women of all descriptions can breathe easy and share community. "Being fat is very isolating," Cox says. "You don't feel confident, you don't feel like going to the beach or bars. If you're a fat chick, you stay home, and that's not good for your mental health." A-Plus is an antidote to all that. "It empowers women to be who they are, to take up space and not feel judged." It's also cheap. Wandering around the sale I meet Maeve, a 24-year-old from Brunswick whose haul today includes a jumper, sunnies and a vintage top, all for $80. And she's not finished yet. "I'm after some stockings," she says. "They're hard to find for fat women. Stockings are only made for tall women." It's same with boots, apparently. "Try finding a boot that will fit this," says another woman, pulling her dress up to show me her triple-sized calves.

Any discussion of fat inevitably returns, like water down a plughole, to two heavily loaded words: health and cost. Most doctors agree that being fat isn't particularly good for you. According to the World Health Organisation, obesity adds to the risk of chronic illnesses including diabetes, cardiovascular disease, hypertension, stroke and some forms of cancer. In 2014, the National Health and Medical Research Council estimated the direct and indirect costs to Australia of obese and overweight people at $56.6 billion a year. Some people regard the obese as a burden on society, an extra cost that fat people themselves should cover. In March 2015, British PM David Cameron proposed that obese people who are unwilling to accept help to lose weight should have their sickness benefits cut. In October, the Australian and New Zealand College of Anaesthetists gingerly floated the idea that obese pregnant women should pay extra to be anaesthetised, since it took eight to 18 minutes longer (the equivalent of an extra $200 to $450) to put them under. This is a touchy subject for fat activists, who say you can be both fat and fit. They also claim that common tests for obesity, such as Body Mass Index (BMI), are flawed, and that your weight in kilograms says nothing about your health. Some also cite contrary research, such as a 2011 project by American physiologist Linda Bacon, which pooled data from over 350,000 subjects and 26 studies and found "overweight to be associated with greater longevity than normal weight". One thing is sure: dieting isn't the answer. Most diets have only a 3 per cent to 5 per cent success rate. Nor is fat-shaming, the logic of which can produce thickets of twisted thinking. "It's totally counterproductive," says Elyse Lithgow, who I meet at the A-Plus Market. Lithgow has been big since the age of eight. She dieted as a teen, but it didn't do much. By the time she started university she weighed 107 kilograms. "I didn't enjoy uni," she says. "I didn't know who I was or who I wanted to be." Soon she found herself eating a lot less. She kept a food diary in which she obsessively counted calories and planned every meal weeks ahead. "If I ever went outside that plan, I would feel terrible and get depressed and start abusing laxatives and fasting."

She lost 40 kilos in nine months, with no exercise. "People kept congratulating me, saying, 'You look amazing' and 'Keep going!' It was bizarre. I had anorexia and was bitterly unhappy, but people were telling me to 'keep going, keep going', no matter what, because anything was better than being fat." Her weight yo-yoed for the next six years. There were long periods of loss and gain and bingeing. "It was only when I found a doctor and psychologist who suited me that I started recovery." Her boyfriend has also been great. "He doesn't care what I weigh." Lithgow concedes that the fat versus health discussion is valid. "You can't pretend the health issue doesn't exist; I have a nutrition degree, I'm not stupid. But all I ask is for people not to judge me solely on my weight but to look at me holistically, at my blood pressure, cholesterol and mental health." Lithgow is happy now. But the battle over her weight has had real casualties. "I've stopped speaking to my father. It was hard to be around him and not feel bad about myself because he thought of me as the person I was in the past, a person who was fat [and who could have been thin]. I've tried on and off to make [our relationship] work but in the last year I've made the decision that it's not going to happen. Which is sad." Fat acceptance is a counterculture. As such, it can be wary of mainstream media, which it blames for peddling an unattainable female beauty norm based on being endlessly youthful and skinny. Among the most wary of all is Kelli Jean Drinkwater. Drinkwater, who lives in Sydney, is the godmother of Australian fat activism, a powerhouse of fat happenings, films and events. In 2013, she started a large ladies' synchronised swimming group, called Aquaporko (motto: "Fierce. Fat. Aquatic."), which she subsequently made into a documentary. She also collaborated as artistic associate on Nothing to Lose, a dance show that premiered at the 2015 Sydney Festival.

I was keen to talk to Drinkwater, but she declined. "I've been burnt by the media before," she told me. This annoyed and baffled me – at least until I came across the psychopathic vitriol that is commonly directed at fat people who speak out, especially on the internet. "The trolling started immediately, from my very first post," Kath Read told me. "I've had people threaten to smash my face in with a hammer the next time they see me on the street. I've had people threaten to chop my head off with a chainsaw. I've had threatening phone calls, and death and rape threats on any online platform you can think of." People have signed up Read to mailing lists for dozens of gyms, obesity clinics, bariatric surgery and diabetes services: "Getting off their databases took weeks of phone calls." People have turned up to her work and spoken to her boss. They have sent her pizza. "The pizza dude shows up and I have to explain I didn't order it." What kind of person does these things? "Anybody. Everybody. It's not just the basement-dwelling Cheeto-eaters. These are otherwise normal people who feel the need to harass fat people." One of the people who trolled Read turned out to be a public servant in Canada. Another time, she caught a woman slipping an abusive note into her letterbox: "She was a law student from the University of Queensland." Trolls commonly assume Read's website is aimed at trying to persuade men to find fat women attractive. "But it's not about that. It's about not living in this mire of self-loathing that many fat women do. It's about shifting the narrative around fatness and the culture of fat hate. It's about being able to walk down the street and not have some guy yell 'Hey fat c...!' from his car."

Of course, fatties can give as good as they get. In 2013, Geoffrey Miller, a psychology professor at the University of New Mexico, sent out the following tweet: "Dear obese PhD applicants: if you didn't have the willpower to stop eating carbs, you won't have the willpower to do a dissertation #truth." The flaming was cataclysmic. Miller's Twitter feed was overwhelmed (he eventually set it to private) and there was an email campaign to have him sacked. New Zealand fat blogger Cat Pause set up a website called F@!k Yeah, Fat PhDs, where hundreds of fat people with PhDs posted photos of themselves. Miller was eventually reprimanded by his university, and sent to something called "sensitivity training". Fatties can also dish it out to one another. Fat acceptance is full of sub-groups, including the "baby fats" (aka "inbetweenies"), "BBW" (big, beautiful women), "bodi-posis", "fatshionistas" and "gainers" (someone who is sexually aroused by getting fatter, and their enablers, aka "feeders"). Not all these groups see eye to eye. "Beauty standards exist inside fat activism as much as they do outside," says Read. "Sometimes there are people who still have internalised fat-phobia and believe that some fat is okay, but not too fat. Or they focus on the 'acceptable' fats: white, smaller, pretty, hourglass-shaped, affluent, able-bodied. That's why plus-size models are so popular: they're the pretty girls, the 'acceptable' side of fatness." But the real venom is reserved for fat priders who make the mistake of losing weight. "You can be ostracised," says Elyse Lithgow. "It's seen as a betrayal. The suspicion is that you were never really body positive in the first place. People can lose friends over it." Take Shelley Bovey, a Welsh author whose early books, Being Fat Is Not a Sin and The Forbidden Body, argued for an end to discrimination against fat people. Then, in 2002, she wrote What Have You Got to Lose? which suggested it was okay to want to lose weight. By this time, she had shed around 42 kilograms, which is when the fat movement went nuts. She was savaged on social media; friends abandoned her. She got hate mail. In the end, Bovey described "the fat and proud brigade" as "neo-fascists".