When Elizabeth Gilbert was writing Eat Pray Love, her blockbuster of self-discovery, she reassured herself, and those closest to her, that "nobody reads my books". The memoir catalogued, uncensored, the depression, disintegration, infatuation and masturbation that followed the breakdown of her marriage and the year abroad she spent trying to recover from it, as well as her relations with her ex-husband, sister, parents and boyfriend. There are currently five million copies of Eat Pray Love in circulation, and Gilbert has had to adjust her position, although she is protected, she says, by the fact that the person she was writing then about is "obsolete". (Her family and friends aren't obsolete, but what can you do?) When she left New York, she was 34, burnt out, a divorced journalist who couldn't conceive of being happy again. She is nearly 40 now, married and living in New Jersey where she and her husband are thinking of getting chickens and, yes, bees.

There are lots of paths to self-discovery, but most of them don't conflate so many lucrative book markets in one handy volume. Eat Pray Love elides self-help, self-improvement, mysticism and a strain of confessional publishing I once heard described as "women who write about their yeast infections", although the real sell is Gilbert's affability as a travelling companion. In Italy she went to language classes and flirted with young men despite her vow to be celibate for the year; in an ashram in India she spiritually purged to get to the "elusive fourth level of human consciousness" while fighting off thoughts about the New York property market; on the beach in Bali she found peace and a new boyfriend. Her combination of dippiness (she describes herself variously as a "flamingo", a "golden retriever" and a "barnacle"), sharp humour and chummy colloquialism was in the tradition of the picaresque hero, while her tone was all women's mag brio. "Hello, God," she said at the beginning of the book. "How are you? I'm Liz. It's nice to meet you."

Save for some lobster fishermen she met while researching a novel on the coast of Maine, Gilbert has, she says, always found it easy to make people like her, a conviction that seems to locate itself in her springy hair and keen expression, so keen that she could be a mime artist. As we walk around the village of Frenchtown, New Jersey, she stops every few paces to enthuse with her neighbours about their dogs and home improvements. In the coffee shop she inquires earnestly as to the function of a large copper pot while the woman behind the counter tries manfully to resist her. ("Oh I love this! What is it for? Is it for coffee?" "No.") "I'd always been the loved and lucky one," she writes in Eat Pray Love, "the favourite of both family and destiny." I'm looking forward to hearing how her sister felt about this.

We leave the village to walk along the path beside the Delaware river. Eat Pray Love wasn't the book Gilbert thought would make her fortune; if any book made it, she thought it would be the one before, The Last American Man, just published in Britain. It is the biography of Eustace Conway, a naturalist who renounced modern American life to live in a forest in North Carolina and an extraordinary character study of a man whose noble aims - to create a self-sufficient community called Turtle Island - were repeatedly foiled by his tyrannical nature. Gilbert spent years on and off with Conway. "The fact is, there was nothing he could do that wasn't interesting to me as a writer. When he became enraging or disappointing, that was interesting. I just wanted to know what he was."

Observers of Conway compared him in the book to Meriwether Lewis, Teddy Roosevelt and Jason of the Argonauts, a self-styled man of destiny still spurred on and ruined by his loveless childhood. Conway gave Gilbert access to everything in his life, including his litany of failed relationships. "He gave me boxes of love letters and diaries. Hate letters. He gave me numbers of women who he knew hated him. Can you imagine? The last thing I'm going to do is give you my ex-husband's telephone number."

To read The Last American Man and Eat Pray Love in succession is to remind oneself that there is no heroic journey for women, no concomitant woman of destiny trope, that doesn't involve childbirth. Perhaps this is the key to Eat Pray Love's success; that after spending all that time watching and listening to the agonies of Conway, Gilbert went off and listened to herself in a way that thrilled lots of women who'd been listening to their own men maunder on for years. The journey started with an act of bona fide bravery: an admission that she didn't want to have children, not with her husband, not with anyone, ever. It's not expressed as categorically as this in the book, and when we find her appealing to God from the bathroom floor while her husband sleeps innocently in the bedroom next door, it reads like an overreaction. She was praying because she didn't know what else to do; she hated her marriage and didn't want to have a baby at that point. But she was only 31 - what was the big deal?

"I think it was a crisis because the pressure was on to have kids," she says. "My ex-husband was very eager to do it. There was no neutral position. Me saying I don't want to have kids was effectively me saying I don't want to be married, if that's what the conditions of the marriage were. I'd also lived a very accelerated decade in my 20s. My career started young and I was really ambitious, and then I had success and I hung out with people who were much older. I think I might have been temporally misplaced, so I thought I was 40. It was a premature midlife crisis."

The end of her marriage constituted the first real failure Gilbert had dealt with. The crisis was so huge, she says, because she was not used to disappointing people or herself, a sneaky piece of self-promotion. She believes that her breakdown was also fanned by grief for the children she'd never have. "When I diagnose my depression now, I think it was partially about saying goodbye to these kids that I always expected to have but already knew that I wouldn't."

Why not? "Because I know my own energies. [Having children] would be the only thing I could do, and that would be devastating to me, because of what else I am and what else I want to do. So it's no accident that I fell in love with a much older person who didn't want to have kids." This is her second husband, Felipe, whom she met in Bali at the end of Eat Pray Love. "It was such a relief. Magic trick! Companionship with no pressure for family! Free built-in stepkids who have already been exquisitely raised by another woman! It's like, how'd I get away with that?"

A lot of people who loved the book for its honesty still thought her first husband got a raw deal. He's barely in it - we don't learn his name or anything about him - but the scale of her flight from him is pretty humiliating. In that scene in the bathroom she whimpers, "I am alone, I am all alone, I am completely alone." The divorce was shockingly bad-tempered and Gilbert won't have it that she did him a disservice. "I had to set up the story, but I also ... Look, no one wants to hear me bitch about my ex-husband, and if they do, they should be paid by the hour. He and I, we don't speak any more. It was really severed and we absolutely disagree on the narrative. There's zero intersection. After months of therapy together, we still absolutely disagreed on what happened and I think the fact that two people can't even agree on the story line is pretty indicative of why we're not living together."

She was, in her opinion, admirably restrained, and any sympathy for the man depicted sleeping while she spoke to God only fortifies her sense of her own forbearance. What about her sister? To out oneself as the favourite child in a family breaks a strong taboo. Gilbert looks genuinely mystified.

"She read it in manuscript. I don't think ... it's weird, I didn't consider that as a self-promotion as much as an indictment of injustice."

We pause here to greet a friend of Gilbert's, then she continues: "We've had so many conversations about that, between the two of us, I feel like it's ... how can I say? It would be the hardest thing in the world to forgive somebody for and the easiest thing in the world to resent somebody for. And her grace in that regard was exquisite and there was no way to say it except to say it."

To say what? "Me admitting that I had an easier life than she did because I had an easier personality and it was easier for people to be sweet to me."

They grew up in rural Connecticut where their parents ran a farm. Her sister liked the outdoor life, Gilbert didn't. "I resented every moment I had to work; I'm a physically lazy person. My sister was tougher and stronger and more disciplined. It was easier to do my chores for me than to get me to do them." After college, Gilbert knew she wanted to be a writer and also that her modest Connecticut background didn't furnish her with enough material. So she took off to have as many story-inspiring experiences as she could. She went to Wyoming to work as a cowhand; she got a rite-of-passage bar job in New York. Eventually, after years of sending out stories, she had one published by Esquire and from then on worked as a journalist and fiction writer, publishing a successful book of short stories and a novel, Stern Men. The account she wrote for GQ about her work in a bar called Coyote Ugly became a successful film.

All of which is hard to square with the often wonder-struck tone of Eat Pray Love, in which she sounds like someone who just stepped off the bus from Kansas, not a New York journalist who had already travelled the world before her year off. Gilbert insists she is a sheep in wolf's clothing. "In New York I had to put on a cynical personality that really wasn't me, to be a little bit more sarcastic than I am." Really, she says, "I have no business being a journalist. I'm the least, I'm the least - I'm the most trusting, I absolutely make a habit of believing anything that anybody tells me about themselves. I've never had any reason in the world to think that anyone has wanted to harm me, or lie to me. I believe whatever is being sold, most of the time."

If there's one thing guaranteed to make a person more cynical, however, it's great success. Eat Pray Love started off selling slowly; it was in the US bestseller list for two weeks then fell away. But instead of disappearing altogether, it hovered outside the top 10, shifting a hefty 1,000 copies a week for a year or so. "And then the paperback went psycho." (The film rights have also been sold.)

It was a bestseller in Poland, France, Holland, Germany, Australia and Brazil before it took off, finally, in the country that held out the longest against it, Britain. Gilbert laughs: "It's full of enthusiasms and exclamations and self-revelations - all that stuff that you guys don't really do." She is grateful that this happened on her fourth and not her first book. "And that I was nearly 40 not 22. That I had a solid relationship. I'm really happy that it happened after my nervous breakdown, not before it."

Still, she has found some of the fallout painful. Lines such as "I stepped through time and I entered the void. I was inside the void, but I also was the void and I was looking at the void, all at the same time" will inspire a certain creepy strain of correspondence, although most people who write to her just want her friendship. "Or they want me to read their book. Or come and speak at their kids' schools. Sell their line of jewellery. Introduce them to a guru. Tell them if they should get divorced. It's been educational for me because I've spent a lot of my life trying to make sure people get what they want when they encounter me. I've always been afraid of saying no to people because I don't want them to be disappointed and dislike me. It's been revelatory to learn that when you say no to people, they're really disappointed and they dislike you."

It should be pointed out that Gilbert's sense of her own beneficence isn't just a matter of style; she puts her money where her mouth is. When she wrote The Last America Man, she divided profits from the book equally with Eustace Conway, a rare gesture from a biographer, and in Eat Pray Love she raised $18,000 to buy a poor woman in Bali a house by emailing her friends and asking for donations. When the woman tried to screw more money out of her, Gilbert cannily defused the situation and they still came out of it as friends. And then there is Felipe, whom she met at a dinner party in Bali and whose worldliness she welcomes as a counter to her credulousness. "In Bali, I'd come back with reports of these magical events and he'd say, 'What a bunch of bullshit.' It was good for me to be around someone like that."

Gilbert didn't want to get married again, but Felipe is Brazilian and there was no other way to get him in the country. After a year of long-distance dating, they moved to Frenchtown and opened a furniture importing business. She has just finished her next book, another memoir that is also "a meditation on marriage". Her second wedding was very different from her first, low key, in normal clothes. "I didn't want this marriage to be based in any sense on an illusion. I've done that. Sanity and clarity are more important for me and I'm willing to give up a lot of shimmer for it. I'm willing to have more boring friends, who are sane." (This might come as news to the sane, boring villagers.) Anyway, she says, she is happy, which is what her readers turned to her in such numbers for in the first place. She smiles her most adorable smile. "It's a very good ending."

• The Last American Man is published by Bloomsbury at £14.99. To order a copy for £13.99, including UK mainland p&p, go to theguardian.com/bookshop or call 0870 836 0875. Eat Pray Love is also available from Guardian Bookshop for £7.99 including UK mainland p&p.