Why Gwyneth's 'perfect life' is beginning to disappear...

Despite these setbacks, Paltrow took to Goop to tell her 150,000 subscribers that she and her staff will be following a "pre-Christmas cleanse" to prepare for the rigours of the party season after "our summers of overindulgence". The detox involves kale juice, carrot soup and balsamic miso root salads. No gluten, sugar, dairy, salt, caffeine or alcohol.

The blog post was classic Paltrow: full of healthy advice, trying to ensure it didn't sound like the pampered delusions of a Hollywood star with an army of staff and determined to carry on even in the knowledge that her words would instantly be republished and ridiculed by many.

She is the A-lister we love to hate. From the time of her tearful Oscar acceptance speech for Shakespeare in Love in 1999 to her shock announcement earlier this year that she and her husband, Coldplay star Chris Martin, were "consciously uncoupling", Paltrow (42), has been mocked and derided.

But this year must truly seem like her annus horribilis. The separation from Martin was announced in March after a year in which they said they had tried and failed to save their 10-year marriage. Paltrow and her two children with Martin, Apple (10) and Moses (8) moved from London to Los Angeles, where the singer now also spends much of his time.

On the surface, the split seems immensely amicable; the couple have been spotted having dinner together, and at a recent Aids fundraising benefit, Paltrow introduced Martin with gushing praise for his musical talent and fathering skills.

Martin briefly split up with his girlfriend, 24-year-old Hunger Games star Jennifer Lawrence, reportedly because she couldn't handle his closeness to his estranged wife. But it has since been reported that he is planning to join Lawrence in London for the Hunger Games premiere.

Meanwhile, Paltrow has been linked to Brad Falchuk, the creator of the TV series Glee, in which she has made numerous appearances.

Dig a little deeper, though, and the "conscious uncoupling" is apparently not going that well. "The fact that Chris got together with someone almost 20 years younger than her - and an actress - has been really hard for Gwyneth," says Hollywood observer Sarah Linas. "It feeds into all her insecurities. She's 42 and that is a hard time for women in her business.

"Jennifer is the actress everyone wants to hire. Gwyneth is in that limbo age - too old to do the action roles or romantic leads, too young, or maybe still just a bit too beautiful, or perhaps just not good enough, to play the big character parts."

Paltrow's most recent role is as a supporting actress in the film Mortdecai, starring Johnny Depp and Olivia Munn, while last month it emerged that Kidman is to replace her in the English remake of the Argentine film, The Secret in Their Eyes. She may still have the star wattage to carry a movie, but her limbo status was reflected in this year's rankings by Forbes magazine of the top-earning Hollywood actresses. Sandra Bullock (50) topped the list, mainly for her hugely rated role in the space film Gravity, while Lawrence came second thanks to her action parts in the Hunger Games and X-Men films, as well as her indie romance, Silver Linings Playbook. Paltrow was fourth (after Jennifer Aniston) with earnings of $19m (€15m), almost half those of Lawrence.

While her combined worth with Martin is estimated at €220m, the balance between them has switched - when they met, she was by far the biggest earner; now he is.

The daughter of the actress Blythe Danner and film director Bruce Paltrow, Gwyneth was brought up among the Hollywood elite and went to a private school in New York before gaining early acting roles as a teenager.

She has insisted that her diminishing big-screen appearances are a result of her own choice to do one film a year so she can be around for her children and focus on Goop. She has written two best-selling cookbooks and is passionate about health and fitness.

However, her lifestyle brand ambitions have also come under attack this year. According to financial reports filed recently, Goop's debt has risen to more than €1.3m. The firm said its directors "are of the opinion that predicted profits will provide sufficient resources to enable the company to continue trading in the foreseeable future".

Goop, which started out as Paltrow's lifestyle blog, is now moving into e-commerce, selling clothes, beauty products and interior designs online. But with her recommendations for plain white T-shirts that cost €75 and expensive sushi delivery services, questions remain about her appeal to her readers beyond the insight into her celebrity lifestyle.

As with her acting career, she is being squeezed on two fronts - old and young - when it comes to Goop. Enemy number one is Stewart. Last month, the 73-year-old doyenne of the US lifestyle market suggested that Paltrow "just needs to be quiet" on matters such as cooking, adding: "If she were confident in her acting, she wouldn't be trying to be Martha Stewart." (Paltrow has even hired her rival's former chief executive to work for Goop.) Enemy number two is Blake Lively (27) who has recently started her own lifestyle blog, Preserve, and who took a dig at Paltrow in an interview in Vogue Australia this summer, saying: "I'm not trying to show you the perfect life or the aspirational life. It's real life. It's not about me."

While Paltrow credits her love of food and cooking to her adored late father's skills in the kitchen, others say it is her fear of ageing that drives her lifestyle. "Her dad died when she was young [he had a heart attack while she was on holiday with him], and from that moment she became obsessed with being healthy and fit," says one source.

"She talks in public about having a glass of wine or a martini, but privately she will then obsess about it for days afterwards and go on a huge detox. It's a very controlled life. Everything is micro-managed in half-hour time slots - food, fitness, even playing with the kids."

And she can be ruthless when it comes to protecting her image. When she learnt this year that Vanity Fair was planning an "epic takedown" of her reputation, she wrote to all her influential friends asking them to boycott interview requests for the magazine, in effect demanding that they never appear in the publication again. Vanity Fair backed down and ran an innocuous profile piece.

The respected Vogue food editor, Jeffrey Steingarten, has written about how he was frozen out from a planned interview with her after he told her he was planning to ask her about why she is perceived so negatively and whether she had had cosmetic surgery.

Other journalists say she can be charming, open and honest in their presence, but perhaps this is simply about protecting her brand.

She has contracts with the make-up company Max Factor and the clothing and perfume giant Hugo Boss - deals that Forbes estimates are more important to her profile and earnings than her film career.

Brand expert John Edwards says: "She still has a huge public profile and, in a way, it doesn't matter whether people like or dislike her - she is recognisable in adverts, she's glamorous, and she's in the news. Advertisers love all those things. Look at someone like Sandra Bullock, who is having a huge comeback at the moment.

"I wouldn't write Gwyneth off just yet."