Born near Atlanta, Georgia, in the buckle of America's Bible-belt, and raised by a Catholic mother and a Baptist father, Julia Roberts last week announced that she'd undergone an extraordinary religious conversion. With the self-confidence that only very major Hollywood stars can truly muster, the 42-year-old actress declared: "I'm definitely a practising Hindu."

Roberts has been visiting temples to "chant, pray and celebrate" with her husband, Danny Moder, and their three small children. "Hinduism is something that I'm very intrigued by and very interested in," she said, adding that in her next life she would prefer to be someone "quiet and supporting", rather than returning as yet another celebrity. In publicly sharing her new-found, and slightly unconvincing, grasp of spirituality, Roberts was at least keeping in character.

In a hugely hyped new film, she will assume the role of Elizabeth Gilbert, the yoga-loving, yoghurt-knitting author of the best-selling memoir: Eat, Pray, Love. The book has graced the bedside tables of seven million readers – the majority of them women – worldwide, and has been a constant presence in the top 10 lists since its publication in 2006. It follows the 32-year-old Gilbert's efforts to escape the tyranny of her urban existence, after finding herself unhappily married and suffering a sort of early mid-life crisis.

It tells how she splits up with her husband, leaves Manhattan – where she's been working as a freelance writer – and sets off on a globe-trotting journey of self-discovery. In Italy, Gilbert learns how to "eat", enjoying fine wine, ice cream, pizza, and embracing her ever-expanding waistline. In India, she decides to "pray" and locks herself away in an ashram for months.

The "love" bit comes in Bali, where in the final chapter of her "search for everything", she falls for a Brazilian-born Australian factory owner called Felipe, who is played in the film by a swarthy Javier Bardem. Felipe eventually returns to the US with her, where they get married and, we must presume, live happily ever after.

Inspired by the book's cult following, and no doubt impressed by the huge success of female-skewing films such as Sex and the City, Sony has thrown an estimated $80m (€62.1m) at making the movie, a huge sum by the standards of so-called chick-flicks. Tens of millions more are being spent on its high-profile marketing campaign.

It was directed by Ryan Murphy, the man behind the television phenomenon Glee, and boasts a hugely extravagant ensemble cast of A-listers. In addition to Roberts and Bardem, the film-makers have signed pay cheques to Billy Crudup, Viola Davis, James Franco, and the Glee star Mike O'Malley. Yet in recent days, as Eat, Pray, Love's star-studded PR machine has begun furiously selling their movie to an expectant world – it will hit cinemas in at least 20 countries – the first cynical whispers of what may soon become an angry backlash have started to be heard. Fans of the novel, which is after all based on the premise that to achieve happiness one must break free from the shackles of 21st-century consumer culture – have been upset, and faintly gobsmacked, at the studio's efforts to use the supposedly anti-capitalist movie to endorse several ranges of stupendously tacky merchandise.

One typical deal involves Fresh, a US cosmetics manufacturer, which has been sold a licence to flog a range of perfumes based on the film's locations. Informing us that "fragrance is a big part of my own spiritual journey", the firm's founder claims they will actually "transport you to a specific destination" in the movie. Confused? Don't be: the marketing blurb adds, for example, that the $32 "eat" fragrance was inspired by the delicate aroma of a Tuscan pasta restaurant. It contains "notes of bright Italian lemon and basil balanced with creamy textures reminiscent of cannoli and tiramisus topped off with sparkling prosecco and limoncello". Just as preposterous, and extravagantly priced, is a range of jewellery and trinkets being sold by a firm called Dogeared, which hopes to sell lonely or fulfilment-seeking fans of Gilbert's book "something to wear, connect with, and take with you as your own story unfolds". It includes a "109-wishes prayer turquoise bead necklace with green onyx", which costs $152 and provides the wearer with "a beautiful reminder to live in love and gratitude".

Elsewhere on America's high streets, Costplus now has an entire section of its outlets devoted to the film. They're selling themed sarongs, bath robes, prayer shawls, furniture, rugs, and pillows. Household ornaments include "meditation bells", Buddha statues made from stone, wood, and terracotta, and a "three-shelf Indian glass curio cabinet" $100 (€78) to keep them all in.

The final insult, given Eat, Pray, Love's emphasis on following one's own path in life, has been the fact that several upmarket travel companies are now running package tours that will transport holidaymakers to exotic locations where they can practise yoga and vegetarianism, just like Julia Roberts. For the princely sum of $20,000 (€15,500), a company called Micato Safaris will take you on an 18-day "inspirational India" tour, involving sessions with Reiki masters, yoga classes, and private sessions with astrologers and "gem doctors" who can allegedly cure illnesses using "the healing properties of gemstones".

The great irony, note critics, is that if a sufficient number of fans buy into these tours, they will end up destroying the very thing they have come to celebrate: the undiscovered nature of the charming locations detailed in the film and book.

One could, of course, argue that it was ever thus: film-makers have been knocking-out merchandise ever since George Lucas released his first Star Wars figurines, and in an era when box-office revenues are flat, studios need all the tie-ins and product placements they can muster in order to turn a profit. But the commercialisation of Eat, Pray, Love may nonetheless herald the acceleration of this ugly trend.

Adding to the negative buzz surrounding the film's release is growing evidence that it is likely to be a critical bomb. The newspaper Variety, allowed to release its write-up early since its audience is largely industry-based, dubbed it "an exotic junk-food buffet that offers few lasting pleasures or surprises, let alone epiphanies". Bad reviews don't always keep audiences away, of course. But even if all seven million people who have purchased a copy of Eat, Pray, Love go to see it at their local multiplex, Sony will still be a long way from turning a profit.

The only woman who won't really mind the criticism is perhaps Elizabeth Gilbert. She recently admitted that the supposedly free-wheeling trip in Eat, Pray, Love (yoga tuition fees and all) had actually been funded by a publisher's advance on the eventual book. It is easy to see it as a somewhat contrived spiritual odyssey designed by a bookseller eager to cash in on a wealthy demographic: middle-aged women who for some reason feel unfulfilled. In which case, one might argue that Sony's entire array of jewellery ranges, memorabilia and package holidays (not to mention Julia Roberts and fascination with Hinduism) are, in fact, strangely appropriate.

Accessories for the soul?

A pair of embroidered pillowcases

"Where will your dreams take you? Anything is possible when your head hits a pillow encased in luxurious cotton from India" ($39.99)

Eat, Pray, Love eau de parfum

"Emotionally charged fragrances designed to be worn alone or layered together, that not only transport you to a specific destination, but also to a different state of mind" ($32 each)

Sony pocket edition eReader

"Throughout your journey of self discovery, what better way to entertain yourself than with this revolutionary library-to-go" ($229.95)

Set of 12 embroidered napkins

"The fun splash of coloured embroidery on one corner gets your attention and starts an intriguing conversation" ($14.95)

Sajen silver and quartz triplet ring

"Be true to yourself and begin your life's adventure today. Inspired by the movie Eat, Pray, Love, this bold ring... features hands holding the 'Ohm' mantra" ($159.90)