Such was the revolutionary vigour of Fat Is a Feminist Issue when it was published 30 years ago, that for a moment the screwed-up relationship between women and food looked like it could be resolved. In Susie Orbach’s urgent, crusading prose, all was illuminated: diets don’t work because they lead only to bingeing; we eat compulsively to try to soothe inner hurts or we get fat as a subconscious rebellion, to opt out of how society insists we look and behave.

It became an instant classic, a student bookshelf staple, and Orbach’s theories entered the mainstream in a thousand self-help bibles. Yet today women and food are more embattled than ever. Obesity and food disorders – which stem, Orbach believes, from one root cause, the perversion of our natural appetites – are epidemic, while female body-loathing now begins in primary school, extending even into the old folks’ home. “I did not expect,” she says, “to be still writing about this three decades on.”

But Bodies, her latest work, is a timely counterblast against our harsh new visual culture, obsessed with the perfection of the physical self. “Our bodies no longer make things,” she writes. “Our bodies… have become a form of work.” They are not given to us by simple biology, but are something we manufacture – through the gym, fad diets or, increasingly, surgery – into an outer form which, we are led to believe, will make us feel better about ourselves.

“When I wrote FIFI [her pet name for Fat Is a Feminist Issue] I was writing about people with particular body issues. Now these are so commonplace that someone who is a compulsive eater is in the normal range. There are kids who don’t eat during the week, only with their boyfriends at weekends. Or diet and binge. It’s become normalised.” Part of the female condition? “At this moment in history, yes. Also, I’m not sure we were into perfection back then. There was just slimness as an ideal. Now there is this expectation to copy celebrities, the images are digitally enhanced, prefabricated, ubiquitous. I think the critical feature is there is no way not to be infected.”

I prepared to meet Orbach with trepidation. Just as American hobos chalked signs outside houses to tell comrades whether to expect a kind welcome, my fellow journalists have left a trail of warnings. Their profiles speak of Orbach’s aching silences, her disdain for personal questions, her loathing of the interview process. When I tell her this, that I barely slept last night for fear she’d be terrifying, she is aghast. “I’m not like that, am I?”

No. But she is wholly measured, guarded and often oblique in her replies. She has decreed that we meet, not at her home/offices in Swiss Cottage, but around the corner in the echoing foyer of the Hampstead Theatre. After each inquiry about her life, I can feel her first conquer a disinclination to answer. It is only weeks after the interview that I learn Orbach last year split up with her partner of four decades, Joseph Schwartz: she has clearly kept this event very close and certainly did not correct any assumption they were still together. Orbach says she is concerned that her public self – her cultural firestarter side – will overshadow the discreet professional shrink. Most of all, I sense she regards the journalistic interview as a shallow, shabby facsimile of what happens in her consulting rooms. Only when I blurt something personal do her brown eyes turn on me with infinite warmth and concern and I contain my urge to tell her all.

Journalists have punished her, she says, for refusing to talk about her most famous client, Princess Diana (of whom more later). Although really none was unkind, just stymied by her silence. “Will Self apologised for his piece,” she tells me, although I thought it, actually, borderline adoring. Is it not more likely she was prickly with the press after being besieged for months by the tabloids in her own home and having her own “secrets” – including a teen pregnancy – exposed? Absolutely not, she says. Later, relating this to a psychotherapist friend, she remarks: “Typical Freudian, refusing to take responsibility for any of their own s***.”

Orbach, at 62, is a minxy dresser, bird-like yet bosomy frame in a tight black twin-set with high-heeled boots and scarlet talons. Even in the women’s movement’s Seventies heyday she was never one for dungarees and workshirts. Although she is half-American and has spent chunks of her life in New York – giving her voice mid-Atlantic intonations – her look is very French. And she is not immune to vanity. The day we meet she has published a piece about obesity in The Times and she scrutinises her byline photograph, dissatisfied it was taken when she wore her hair straight.

Fat, she says, is now more than a feminist issue: it is, among many things, a class question. “Thinness,” she writes, “is a means to enter what on the surface appears to be a new classless society.” The mothers pushing pies through school fences to upset Jamie Oliver’s best efforts are rebelling against finger-wagging disapproval: “Fat can be a form of protest. ‘I don’t want to be in your party, I am here and I’m going to stay here.’”

And while men are now also prey to body fears, the pressure remains harshest on young women. “All of the girls I see as patients – and I have a daughter too – feel they must produce good marks, produce the great body. They are much more involved in a production of the self than in living. There are so many young women who tip over into being a facsimile: they don’t really inhabit their lives or their bodies.”

How did she stop her own daughter – Lianna, 20, a student in New York – falling prey to this obsession? “In some ways, I was a bit of a fascist,” she says. “If we had an au pair I just said, ‘You are never to stand in front of the mirror and say, “I hate my body,” in front of my children.’ I want my children to think bodies are OK, that the default position is not that there is something wrong with them. Which is what little girls observe their mummies doing all the time. I didn’t want some 21-year-old pumping that into my kids.”

It must be heavy weather for children having two psychoanalyst parents – their father Schwartz is also a therapist. Orbach smiles and recounts how her son Lukas, now 24, fed up with being made to analyse whether Josh at nursery hit him because, really, he was afraid, finally exploded. “Mum,” he said, “why do we have to be a feelings family? Why can’t we be a football family?”

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