Intermittent fasting? So last week. It's all about alkaline eating now, thanks to Victoria Beckham. Earlier this month she dispatched an enthusiastic tweet about the Honestly Healthy cookbook, which was given to her by her friend, the interior designer Kelly Hoppen, who is the mother of the book's author, Natasha Corrett.
"She [Beckham] eats an alkaline diet anyway," Corrett, a vegetarian chef, says. "She read it from cover to cover, and she loves what we do, so she very kindly tweeted about it."
As a result, the book shot into the bestseller lists and holds the number one slot on Amazon's list of healthy eating titles.
"It went viral," says Vicki Edgson (55), a nutritionist who is the book's co-author and godmother to Corrett (29).
"Within 24 hours, sales had rocketed to the point where I was giving a talk on alkaline eating and I couldn't get hold of a copy myself – it had sold out."
According to its proponents, eating an alkaline diet is easier for the body, because our blood pH is naturally alkaline. But a typical Western diet contains many acid-forming foods – meat, dairy produce, sugar, breads, biscuits, coffee and alcohol – leading to internal stress on the digestive, cardiovascular and nervous systems.
"All the degenerative diseases are more likely to develop," Edgson says.
Gwyneth Paltrow, Jennifer Aniston, Miranda Kerr and Kirsten Dunst are all, reportedly, fans of alkaline eating. Sienna Miller definitely is – possibly because she is Corrett's stepsister (Sienna's father Ed Miller married Hoppen, but they are now divorced).
The Honestly Healthy delivery service costs £750 (€875) for an 18-day supply of alkaline vegetarian cuisine, offering treats such as chia seeds with fruit kuzu compote, veg burger on a bed of lemon kale served with carrot chips and raw hemp granola bars as a snack.
Corrett's clients include Kelly Holmes, Lisa Snowdon and Robbie Williams, who endorsed her cooking as "healthy yet ridiculously delicious".
"I'd say about 70pc of my clients are A-list celebrities," she admits.
The Beckhams like her green juice and her soup, she says; the swimwear designer Melissa Odabash raves about her red rice and beetroot risotto.
So why is alkaline eating so popular among the A-list? "Because naturally you stay at your own body weight. You have clear skin, shiny hair, good nails – it's what happens on the inside. Your food is your medicine," Corrett says.
And there's less flatulence. Perhaps they should have called it the Red Carpet Regime . . .
Both women are excellent ambassadors for alkaline eating. Edgson is a size 10, Corrett a size eight, and both are clear skinned and bright eyed, with manes of glossy hair.
It was not always thus, apparently. Corrett describes herself as a reformed "carb junkie".
In the summer holidays, she worked for her father, the restaurateur Graham Corrett, at his London restaurant, Le Boudin Blanc.
"I look back at photographs and my weight went up and down, up and down. I tried every diet going," she says.
"I did the starvation one, the maple syrup one; I finished that and had a pizza; I did protein only ..."
Then she injured her back and went to see Dr Joshi, the health guru favoured by A-listers including Paltrow, Patsy Kensit and Sadie Frost.
He told her her body was highly acidic and suggested an alkaline detox diet of wholegrains, vegetables, nuts and green tea.
"I'd decided not to do any more diets, but he said, 'Trust me. Give it 21 days – it's going to be your life after that.' And a week later, I felt incredible."
Since then she has lost two stone and has stabilised at size eight.
It was the menopause that persuaded Edgson of the benefits of an alkaline diet.
As a nutritionist and co-founder of the Food Doctor brand, she assumed she knew how to eat well.
"But I found that what had suited me in my thirties and forties no longer did. For the first time in my life, I started to gain weight around my middle and I couldn't shift it," she says.
It was only when Edgson started eating according to alkaline principles that her weight started to fall.
"If someone had said you'll end up being vegetarian, I wouldn't have believed you. But I couldn't look at a steak now."
The pair launched their Honestly Healthy food range in Selfridges in 2011, and their book was published last summer in the UK. This summer Corrett is opening a second kitchen in Manchester.
Corrett and Edgson are adamant their alkaline eating regimen is not just another celebrity fad, but a way of life.
It contains all the three food groups, and it's enough, apparently, to eat alkaline 70pc of the time to reap the benefits.
"Vicki and I don't live in a cave in the Himalayas. We like to have a glass of wine or eat a pizza occasionally," Corrett says.
"You make little changes. If you're a white bread person, move to brown, then wholegrain, then spelt, to rye, so by the time you get to sprouted barley bread it's not a massive shock."
Whether you buy into alkaline eating or not – there are plenty of sceptics claiming that what you eat has little effect on bodily pH – a diet lower in processed foods, white flours, saturated fats, sugars and alcohol sounds sensible.
Which is more than you can say for the maple-syrup detox.