The Christmas I was nine, what I really wanted was a sparkly rainbow My Little Pony and a corset. I didn’t like My Little Pony – I have always regarded large animals with trepidation and was immune to all horsiness, real and imagined – but I was being bullied at my school in northern England and had observed a correlation between social status and the possession of garish plastic horses. The bullying was all between girls, no violence but months of ostracism. If anyone spoke to me, the ringleaders punished her. If anyone accidentally touched me or my possessions, she ran around wiping off the “Sarah-germs”. If I spoke in class, they mocked, but mostly they pretended I wasn’t there. I soon learned not to speak at all, not to make eye-contact, to stay quiet and hunched. Everyone was happier if I didn’t exist. At all times I carried a book, several books to get me through the day, and I spent every possible moment in those paper worlds.

I read so much and so fast I couldn’t be choosy, ranging from the Chalet School to Wuthering Heights, finding particular comfort in the exotic domesticity of Anne of Green Gables and Little House on the Prairie but also foraging a secondhand education for myself: Anne Shirley quoted Keats, so I read Keats; Keats wrote about Shakespeare, so I read Shakespeare. I could go on my own to the suburban library, there were some books at home, jumble-sale novels were pocket-money prices. Worlds beyond worlds opened, as long as I didn’t look up.

My mother, who deplored garish plastic but understood something of the situation, bought me the brightest, most glittery My Little Pony she could find. It had gold stars on its backside and a nylon rainbow mane. I recall moulded wings and a unicorn horn, a plastic brush for grooming – which was how the other girls, huddled around desks, spent breaktime. In January, I put it in my schoolbag with the textbooks I didn’t understand and the exercise books that charted my failures. When I took it out, the girls laughed and drew closer together. Pathetic, who does she think she is?

I’d like to say that I wanted the corset for precocious punk-rock reasons, but of course I wanted the corset to make myself smaller. There was a passage in Little Town on the Prairie describing how it felt to wear one, the pain and constricted breathing, Ma’s pride in Pa being able to span her waist with his hands, in her discipline in wearing hers day and night. Every woman I knew wanted such a waist, and in the 1980s corsets would have been cheating. To be a woman was to be on a diet. Mothers had special food, Ryvita and fat-free cottage cheese, grapefruit and celery, rumoured to use more calories in digestion than it provided. Women were supposed to be hungry, it couldn’t be helped. If women weren’t hungry they’d be fat, and no one needed to explain why fatness was bad. I heard the same truths at home, at school, in the magazines to which my mother ambivalently subscribed, from my grandparents, from advertising. It was self-evident: controlling weight and appetite was a life’s work for a woman, work that had started before I could remember. By the time I was four I knew to limit my biscuits at playgroup. I knew that the most pleasurable foods were wrong and that it was bad to eat them, though also that they would continue to be offered, as tests of strength and purity that almost everyone failed.

I knew better than to ask for the corset, but for a few weeks I tried fastening a belt tightly around my waist day and night. Either Ma was wrong about constriction being good for the figure or a real corset was needed, because all that happened was abrasion and pain. There was no way around the need for self-denial, no physical restraint to which I could outsource the work of thinness.

And then I caught flu. My family didn’t do illness. Health was strength and strength was virtue, moral and physical vigour indistinguishable. People who said they were ill were mostly weak or attention-seeking and in either case should pull themselves together. But I had a real, measurable fever. I couldn’t eat, or even read. For the first time, I had days off school, like the other girls, the fragile and lovely other girls, and when I felt better I found I was thinner. Look, I said to my father, my waistband is too big, I’ve lost weight. Well done, he said, now see if you can keep it off. He woke early to run and do sit-ups, despised – but loved – cakes and desserts, frequently praised the thin and condemned the fat; he was of his time and place, doing his best, no blame. (He does not remember it this way. I might be wrong. I am, after all, a novelist, who makes things up for a living.)

I could keep it off. I could lose some more. Many things that were easy and obvious to my peers – maths, ballgames, what to do with a plastic horse – were obscure to me, but I turned out to be good at what was then called “slimming”. I knew how to slim. Every girl, every daughter, every granddaughter, knew how. Slimming was giving up all the food that was mostly for men anyway, meat and cheese and eggs; all the food to which women were particularly vulnerable, cake and chocolate and sweets; all fats and all sugars. Our mothers had “calorie books”, listing in alphabetical order every foodstuff known to middle-class provincial England, with the calories per ounce. Mine is the sandwich generation of decimalisation, grams and kilos at school, pounds and ounces at home, and I became, at least, very good at mental arithmetic. I stole my mother’s book, handbag-sized, a bright yellow cover with a picture of a tape measure snaking across the front, 24, 25, 26, waistline. I memorised it along with my times tables and key dates: seven sevens; the birth and death of Queen Victoria; calories in a small, medium and large apple. I fear calories may be among the last things I forget. I fear I may go to my grave with the tally running at the back of my mind, like a ship’s engine.

I’m sure that now there are daily calorie limits for nine-year-olds to lose weight, but then the instructions in my mother’s diet book pertained to adults – women allowed about what they’d have had towards the end of the wartime siege of Amsterdam, double that for men – so I didn’t have a number. As low as possible. Nothing at all. I’m slimming, I said, give me a smaller portion please, no, less than that. No crisps for me, thanks, I’m on a diet. Hunger numbed my shame and humiliation about the bullying and about being the stupid one in a school for clever girls, and for the first time, the adults around me were full of praise. What self-control! Isn’t she good? How much have you lost then, love? It was months before the mother of a birthday girl, seeing me virtuously declining ham sandwiches, iced gems, chocolate fingers (even with Hula Hoops threaded along them), asked if there was anything I would like to eat. There was a dish called a “hedgehog” on the table, half a grapefruit spiked with cocktail sticks each holding cubes of cheese (too high in fat) and tinned pineapple (too high in sugar). If the other half of the grapefruit was still around, I said, I might eat a little of it when the others had ice-cream and jelly. Come into the kitchen, she said, let’s find that grapefruit, and when we got there she said how long are you going to stay on your diet, how thin are you hoping to get, do you have a stopping point in mind? I shrugged: silly questions, who cared?

But I did stop, that time. When I went back to school after the summer, the bullies moved on to a girl whose mother was dying and a girl who had recently arrived from Lebanon with a veiled mother, no father and unnatural prowess in maths. I thought the bullying settled because I had solved the problem, because I had been too fat and now I was thinner, but 40 years later it seems much more likely that the change was in my confidence. The size of a person’s body never justifies bullying, but in fact mine was unremarkable, has never been noticeably large, nor, for more than brief, dangerous, periods of crisis, noticeably small. In starving I had found something I was good at, that made me feel better, something the grownups valued and even envied.

Both the reading and the hunger were with me for life, a wild freedom and a dark trap, but I think now that it’s not quite so neat. The protagonists of the girls’ canon, from Joey Bettany of the Chalet School to Jo March of Little Women, from Jane Eyre to Esther Greenwood of The Bell Jar, were ostentatiously thin, and not because their high minds were distracted by the vanity of slimming. Literary heroines were metabolically as well as intellectually and morally superior to the young reader. They pulled off the impossible feat of not thinking about food while remaining so small that thinness was their defining physical characteristic. “No matter how much I eat,” Esther says, “I never put on weight.” Taken out for lunch in New York, “[I] picked the richest, most expensive dishes and ordered a string of them … I made a point of eating so fast I never kept the other people waiting who generally ordered only chef’s salad and grapefruit juice because they were trying to reduce. Almost everybody I met in New York was trying to reduce.” Almost everyone I met in northern England 50 years later was also “trying to reduce”. Not being blessed with Esther’s superpower, I had to struggle along with them, experiencing every menu, every mouthful, as a battle between good and evil. In later life, fortunate also to be taken out to lunch on expense accounts, on good days I’d eat well in joyful rebellion but there were bad days when I’d play the game of what I’d choose if I were Esther before ordering whatever allowed me to perform participation in the meal while minimising calories. Mine’s a chef’s salad and a grapefruit juice, please. Jane Eyre, invited to join dinner parties at Thornfield, skulks in corners black-clad and skinny, judging the opulent clothes and curvy bodies of her rivals in love; later she will look with disgust on fat, mad Bertha Mason, the original madwoman in the attic, and on Bertha’s muscled, porter-drinking carer Grace Poole. I wanted to be Jane, Esther, Jo but I knew I was really hysterical, greedy Bertha; Anne Shirley’s dim, cake-loving friend Diana; at best Jo’s plump, frivolous sister Meg. I knew that my failure to be thin was inseparable from my failure to be clever and to control my emotions.

It escaped my notice as a child but does not now that Bertha is mixed race and Grace working class, that the ideal female body displaying the perfect control of the ideal female mind is racialised and classed. Judeo-Christian culture has demonised women’s appetites and fetishised our restraint from Eden onwards, but, as scholars of race studies taught me, the particular iteration of diet culture that we now endure originates alongside the 18th-century slave trade. To quote Sabrina Strings’ Fearing the Black Body: “abstemiousness in England during the 18th century laid the groundwork for moralising surrounding the oral appetites that would be seen in subsequent eras”. Modern white femininity centres around thinness, abstinence and fragility. The 18th-century cult of “sensibility”, celebrating refined emotions and physical delicacy, is the precursor of modern “wellness”, which embraces restriction and vulnerability. Both sensibility and wellness are displays of racial and class privilege; neither makes sense without the mirror image of the Black and/or working-class body imagined as tough and greedy. The women harmed most are those to whom whiteness and fragility are least accessible, not me. One form of supremacy cannot be separated from another. I learned my own whiteness as I learned femininity, as I learned class, as I learned hunger, without noticing and without questioning. In “slimming” I became an accessory to oppression, performed values I abhor. Intentional weight loss makes me complicit with hierarchies I reject.

It is a shame that, like most insights, this one did not make it noticeably easier to behave differently.

• My Good, Bright Wolf: A Memoir by Sarah Moss is published by Picador on 29 August (£18.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply.