In the opulent headquarters of Roll International Corporation, on the fault line between Santa Monica and Beverly Hills, Lynda Resnick is telling me proudly about POM Wonderful - the juice that stole America's hearts and became the health-drink sensation of 2005. 'Never in my wildest dreams did I imagine the bottle would become the famous little character that it has,' she says, in a Jewish-American voice pitched - like her age - somewhere between Ruby Wax and Joan Rivers. 'When you pick it up, it's hard to put it back on the shelf,' she rasps, clutching the bulbous figure-of-eight as Eva Longoria did in an episode of Desperate Housewives earlier this year. 'It just fits in your hand, it's fabulous.'

Though designed to resemble two pomegranates stacked one on top of the other, the bottle - iconic as a Marmite jar, coveted by everyone from Will Smith to Jennifer Lopez - may have another secret precursor. 'It's Mother, it's the female form,' Resnick declares. 'It looks like me, which is why I'm so popular! I was convinced it would be like the Venus of Zachendorf.'

I can find no reference to such a work but she probably means the Venus of Willendorf - the Paleolithic limestone statuette of a fleshy, large-breasted woman excavated in Austria in 1908. Whatever the inspiration, bottles of POM have been flying off the shelves quicker than Resnick's company can fill them. Though Roll International, which owns POM Wonderful, is reluctant to discuss figures, the Beverage Marketing Corporation estimates that sales have totalled $50 million (£30m) since the product launched in 2003. To meet demand for its juice (and the fresh pomegranates which it also grows and sells), POM Wonderful has planted 6,000 acres of orchards in the sun-drenched San Joaquin Valley - the agricultural crucible of California. That, according to the Pomegranate Council - a non-profit trade group in San Francisco - is more than half the total crop grown in the US.

It's a colonisation that took root 15 years ago, when Lynda Resnick and her husband Stewart acquired land in the valley. Then, a handful of pomegranate shrubs grew naturally among the almond and pistachio trees that have also been turned into a lucrative business. Lynda had read about the fruit's reputation as a mystical cure-all and began to explore its market potential; by 2000, when the shrubs produced their first fruit, she had hatched a plan to make California the country's biggest producer and POM Wonderful the pomegranate's Coca-Cola.

Britain, too, has felt the effects of pomegranate power. Available in 108 Waitrose stores, branches of Budgens and sporadically at Fresh & Wild, POM Wonderful proved so popular in early November that Waitrose ran out of stock. Meanwhile, homegrown brands such as Pomegreat - a juice drink, rather than a pure juice, available at every major supermarket - have benefited from the hype. 'We're selling more than a million litres a month,' says Adam Pritchard, MD of RJA Foods, 'compared to 2,000 when we started. Most of that growth has been in the past 12 months. It's been the year of the pomegranate.'

Tesco sells 500,000 litres of pomegranate juice every week - a 300 per cent increase on 2004. Last month, Marks & Spencer launched a 100 per cent fresh juice (declared 'the gold standard for fruit drinks') to rival POM, confirming that the ruby-red upstart is big business. 'Two years ago, nobody in America knew what a pomegranate was,' Lynda Resnick reminds me. 'Now, we're in Wal-Mart for God's sake, we're in Costco, we're in 7-Eleven. I want POM Wonderful to be within arm's reach of everyone who wants it. That is the biggest service I can do.'

It's a mission statement at odds with how POM is perceived: the darling of Hollywood A-listers and readers of Nylon, an elitist elixir - costing a preposterous £3.29 per bottle - added to 'pomtinis' (the official cocktail at the 2005 Oscars) and packed into goodie bags at the Vanity Fair party. 'Of course I know everyone in the world,' says Resnick, 'every mogul, every movie star. You've no idea, the people on my VIP list who drink it - but that doesn't make people buy a second bottle; they do that because they love it. Why would they bring us back to the Academy Awards every year, why would the Golden Globes insist on having it? People don't buy it because I'm in the know or a small celebrity in the big pond of Hollywood. The average consumer in Des Moines doesn't know who I am.'

In Derby and Manchester, too, consumers may have forgotten who Lynda Resnick is. In 2004, she and her husband Stewart became household names when they successfully sued the Princess of Wales Memorial Fund for $25m (£14m) in a dispute over Diana memorabilia, jeopardising the charity's future. In fact, the fund had earlier - and mistakenly - tried to stop the Franklin Mint (another Roll International company) selling such items as the Princess Diana Porcelain Bride Doll on the grounds that the charity owned the 'exclusive rights' to the Princess's name and image. The fund lost and the Resnicks counter-sued for 'malicious prosecution' (the documents lodged with the Los Angeles court had described them as 'vultures feeding on the dead'). Even Rosa Monckton, a close friend of the late Princess of Wales, described the fund's first legal battle with the Resnicks as 'absolute insanity' because the charity stood no chance of winning. Magnanimously, the Resnicks settled out of court on the first day of their lawsuit and no money exchanged hands. Instead, a statement was issued saying the $25m would go to charities decided jointly by the memorial fund and the Resnicks, particularly causes 'that resonate with the memory of the Princess'.

In court, it emerged that the Resnicks had their own charitable body, the Resnick Foundation, which had given £25m to charity in eight years - including £1m to Great Ormond Street Hospital in London. Mind you, they could afford it. Stewart Resnick's wealth is estimated at $890m (£513m) and the couple's assets include not just the Franklin Mint - once the world's largest collectables firm - but Fiji Water, Teleflora, Paramount Farms (pistachios, almonds) and Paramount Citrus (oranges). As friends of Bill Clinton, the Resnicks donate to the Democratic Party and sit on the boards of several museums. A clinic in Los Angeles was recently named after them - the Stewart and Lynda Resnick Neuropsychiatric Hospital. Their taste for French and Italian art from the 17th and 18th centuries is evident at their £10m mansion on Sunset Boulevard - described by the writer Howard Blume as having 'the tasteful opulence [that] exudes a tincture of Versailles - only better kept.'

It's a world away, aesthetically, from the Guardian of Destiny Gargoyle - a pewter monster crouching on a crystal ball - that helped the Resnicks earn their millions: at home, the collectibles are more Bulgari than vulgari. How else could the 'Beverly Hills billionaires' (as the New York Times described them) hold their heads high in the art world? Lynda Resnick certainly does. What's more, with her vivacious manner and dark, business-like Bill Blass suits (a penchant that has earned her comparisons with 'a little general'), she has the personality - and the financial clout - to convince corporate America of almost anything.

'I'll tell you my trade secret,' she says, when I ask how she insinuated her plastic bottles into the chillers of 'fresh produce' aisles in US supermarkets (on the grounds that it was 100 per cent fruit with no artificial additives or cheap filler juices such as pear or grape). Somehow, her trade secret doesn't surprise me. 'We went to the very top of every organisation and spoke to the CEOs,' she says. 'Once they saw the packaging, understood our marketing and tasted the product, they couldn't say no. If we'd let a bunch of brokers run around, talking to low-level grocery people, they'd have been afraid to take the idea upstairs.'

It was a stroke of marketing genius. While dozens of juice drinks, from Ocean Spray to High-C, stood side by side with identical red cartons, Resnick's maroon-brown sputniks sat in an arresting pile close to the fresh pomegranates (available in America from September to December) and chiming with their spherical shape. It was a way of identifying the juice with its provenance - helped by the fact that the most popular variety of pomegranate grown in California is called Wonderful, linking the fresh product and its juice as if POM had invented the fruit. Even Resnick concedes she didn't have the wherewithal to do that. 'It's easy to be a genius,' she says, 'and people think, "my God, you're a genius for doing this" - but only God can make a tree. It was already a perfect product.'

Some might disagree, since the fruit itself - cultivated not just in California but throughout Asia and the Middle East and parts of Spain - is notoriously hard to eat. Most people can't be bothered, hence the success of commercial juices. Constructed like a large, knobbly apple with a leathery shell instead of a skin, pomegranates contain hundreds of glistening, jewel-like arils (edible seeds) housed in sacs of pithy membrane. The best way to extract them is to cut off the crown (like a stalk), lightly score the fruit's surface and soak it in a bowl of water for five minutes. Keeping the pomegranate immersed so its juices cannot stain, break it apart with your fingers and pop all the seeds out of their casings; the pithy membrane floats to the surface, where it can be skimmed off, while the arils sink. Pour them into a sieve, drain them and you have a perfect crop for a snack, to sprinkle on cereals and salads or for a pomegranate risotto - a dish mocked by Gordon Ramsay when he saw it at the Glasshouse Restaurant in Ambleside. Jamie Oliver is a fan and, with their sensuous allure, the seeds are drooled over by Nigella Lawson.

'A pomegranate is filled with rubies when you open it up,' Lynda Resnick says theatrically, glossing over the problem of extraction. 'Diamonds may be a girl's best friend - but not for me. I love rubies, they're great over necks, you know.' In antiquity, they were thought to be great for other parts of the anatomy as well and became a symbol of fertility (in women) and virility (in men). They appear on the coats-of-arms of venerable medical colleges and, in more rigorously scientific times, have been found to be rich in antioxidants. These are the natural compounds that mop up 'free radicals', the damaging molecules coursing through our bodies (some generated by a junk-food diet, pollution and cigarette smoke) which are implicated in heart disease, stroke, cancer and ageing.

The best-known antioxidants are vitamin E, vitamin C and folic acid - all abundant in whole pomegranates and their freshly squeezed juice. One pomegranate supplies 40 per cent of an adult's daily vitamin C requirement and the juice has three times the antioxidant properties of red wine or green tea, previously regarded as the best protection against heart disease and lifestyle illnesses. Blueberries, blackcurrants, cranberries, red grapes, red onions and plums are also rich sources of antioxidants, particularly those known as polyphenols - indicated by their red pigment. The best dietary advice is to eat a wide range of fruits and vegetables, including some that are red - but this does not boost sales of pomegranate juice, the first step in Lynda Resnick's crusade to bring heart health to the masses. What is needed is hard scientifc evidence that pomegranate is an unrivalled panacea.

In 1998 the Resnicks set out to prove just that, using their influence deep within American and Israeli society to find a unique selling point for POM Wonderful years before it was launched. First they contacted Dr Michael Aviram, head of the lipid research programme at the Technion Institute in Haifa, Israel. For 20 years, he had been looking at ways of preventing and breaking down deposits of plaque in the arteries - atherosclerosis - which cause cardiovascular disease. Searching for natural antioxidants, he tested '20 different things' before alighting on the pomegranate which, although it doesn't lower bad (LDL) cholesterol, limits how much of it gets 'oxidised' - the first stage in the formation of plaque, which can narrow arteries or become unstable and break off, leading to heart disease and strokes. With the Resnicks' help, Dr Aviram embarked on further studies. Another key ally was Dr Ephraim Lansky, also at the Technion Institute, who had developed a pomegranate pill called CardioGranate, sold 'in a fancy bottle out of Israel, mainly to the States', according to one British researcher. Most impressively, POM Wonderful managed to hire the eminent Dr Louis Ignarro, a Nobel laureate who received his prize for work on nitric oxide, a ' factor' released by the lining of blood vessels which acts as a vasodilator (opening up vessels in the same way as Viagra) and improves cardiovascular function. His work and many other projects are co-ordinated by Dr Harley Liker, medical director of POM Wonderful and a physician at the University of California, Los Angeles (UCLA) - Stewart Resnick's old college, and a recent recipient of more than $3m (£1.75m) from the Princess of Wales Memorial Fund legal settlement. To date, the Resnicks have lavished $10m (£6m) on scientific studies - four times what POM Wonderful spends on advertising each year - at 18 medical institutions worldwide, and committed $8m (£5m) to future projects. Though funding research is not unique for a food company, the sum is staggering. 'That's ridiculous,' exclaims Adam Pritchard, MD of the British company that makes Pomegreat, when I mention the $10m figure. 'We're hoping to begin our own work on something similar - but we're not spending $10m. The Scottish Crop Institute is using our product in a cancer trial - and we're not paying a penny for that. I could get the best result in the world with $10m.'

In the past two years, the Resnicks' investment has paid off - lending credibility to the heart-shaped 'O' in the word POM on their packaging. In 2004, Dr Aviram published a paper in Clinical Nutrition, showing that plaque in the carotid arteries (supplying blood to the brain) was reduced by up to 30 per cent in patients who drank POM for a year, as opposed to sugar water. In March this year, Dr Louis Ignarro and colleagues showed that antioxidants in pomegranate juice help maintain levels of beneficial nitric oxide - his Nobel prize area - in a POM Wonderful-funded study in the Proceedings of the National Academy of Sciences. Also this year, Dr Dean Ornish published a paper in the American Journal of Cardiology, looking at blood flow to the heart in 45 patients with blocked arteries who were given pomegranate juice or a placebo.

'Over three months,' Dr Liker reveals, 'those on the juice showed a 17 per cent improvement in blood flow while those on sugar water got worse by 18 per cent.' Such studies are peer-reviewed - meaning they are held up to scrutiny by experts - and published in respectable journals (and therefore subject to checks on integrity, including the ethics of funding). However, they are not as watertight as the Resnicks and their team would like. 'You can show all sorts of things in 10 people or 25 mice,' says Dr Richard Bogle, senior registrar in cardiology at Hammersmith Hospital, London, 'but when you start extending it across big populations, it's different. You find the magnitude of effect is smaller than you would have predicted from small-scale studies, or that there is no effect at all.'

That is one big problem with the antioxidant story, he says. In particular, the Big Three - vitamin C, vitamin E and folic acid - have proved disappointing in large-scale trials. 'Nevertheless, antioxidants are a recurring theme,' Dr Bogle explains, 'because companies realise that this is a pathway well trodden by the public: they have this idea that antioxidants are a good thing, the elixir of life, anti-ageing, anti-heart disease. There is no real evidence.' Dr Bogle's specialist area is the endothelium, the lining of the blood vessel, known to produce 'factors' (chemical substances) that regulate blood flow and the permeability of the vessel, and stop platelets and white blood cells sticking to it. In people with high blood pressure or diabetes, endothelial function is compromised, leading to heart attacks and strokes.

'Some of the foods I am interested in, one of which is pomegranate juice, appear to have some effect on restoring the function of blood vessels,' Dr Bogle explains. In due course he hopes to do trials with pomegranate juice - but 'it's not my top priority,' he adds. What is not in doubt is the general orientation of pomegranate research, which focuses on the juice's ability to block the oxidation of LDL cholesterol - the process that forms life-threatening arterial plaque. 'What you get initially is lots of small studies like these, and they all point in the right direction,' Dr Bogle says. 'Then hopefully, someone like POM Wonderful comes along and funds a proper study that can answer our questions.'

Whatever the science, this is not the end of the pomegranate frenzy. While Lynda Resnick continues her crusade, others are launching new products or refining existing ones. Like POM Wonderful, the new Fresh Fruit in a Bottle from Marks & Spencer is a 100 per cent, refrigerated juice with five pomegranates in every bottle. Uniquely, it is made from the freshly pressed fruit rather than a concentrate that is stored, rediluted and pasteurised (losing its vitamin C), as POM is. Meanwhile, Pomegreat - a drink made with 'fruit extract', 30 per cent pomegranate juice (from concentrate) and aronia berry - will be joined by a new product in January, a fresh product in the M&S vein.

'Pomegranate juice has staying power,' Lynda Resnick concludes. 'It's not a fad. Once people have tasted POM Wonderful, they say they are addicted - and it's a good addiction to have.' Perhaps the fruit's dangerously compelling quality is something she has mentioned to President George Bush. In May, Bush proposed that President Karzai of Afghanistan grow pomegranates instead of heroin poppies.

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