Temptation can never be far away for a man married to Nigella Lawson, the delectable domestic goddess. Who would not want to sample her vanilla apples with sweetheart croutes? Taste her duck breasts with pomegranate and mint? Or trifle with her passion fruit fool?

As for her lunchbox treats (page 266 of her latest tome, Nigella Express) – the thought is enough to make you quiver.

So our admiration for the will-power of her husband Charles Saatchi should know no bounds. Saatchi, the millionaire art collector who had a hankering for pickled shark, has spurned his wife’s cooking and been on a severe diet. So severe it practically breaches the Geneva convention.

In a matter of months, he has lost four stone. While his wife grows ever more Rubenesque, he has gone all Giacometti.

What’s his secret? Surely it is not possible for a man to lose weight when his wife can knock up rib-sticking stir-fry (“there’s a good amount of meat in this”) followed by roly poly pudding (“eat with either cream or ice cream”), without even smudging her lip gloss? For weeks there has been speculation about how Saatchi managed to slim down. He turned vegetarian, said some observers. He stopped consuming endless frappuccinos from Starbucks (about 190 calories a time), said others.

Some drew comparison with Nigella’s father, Lord Lawson, the former chancellor. When Lawson quit frontline politics and cutting taxes, he lost five stone by cutting out sugar, alcohol and dairy products – and wrote his own diet book.

For Saatchi the answer was even more radical: he says he gave up pretty much everything except eggs.

“It was glorious getting very fat,” the reclusive Saatchi confessed to The Sunday Times. “When you lose the last of your vanity and eat Shredded Wheat, Weetabix, Maltesers, Topic bars and anything else you want, all day, without guilt, it is heaven.”

It confirmed what Nigella had once said: “Charles doesn’t really like proper food. He prefers a bowl of cereal. We often climb into bed together with a bowl each of cereal, ice cream and biscuits.”

To which one can only say: crumbs.

However, there comes a time when climbing into bed with all those bowls of cereal still hanging around where your six-pack used to be gets a little tricky. Saatchi reached that point last year.

“The discomfort and humiliations of being obese finally won,” he said. So he adopted radical action. “It took me 10 months of eating only eggs for breakfast, lunch and dinner to shift it. I am still not much to look at, but I have become cringingly vain and hold the world record for the highest level of cholesterol ever seen in anyone still with a pulse.”

Saatchi is known to like a joke – never mind a yolk – and not everyone can believe he survived for 10 months on nothing but eggs.

“I love eggs, particularly bantam eggs and quail’s eggs,” said John Burton Race, the award-winning chef of the New Angel restaurant in Dartmouth. “But I’m not sure I believe him. If he’s insisting it’s just eggs, I’d get him a psychiatrist. And some laxatives.”

Saatchi’s claim is not impossible, though perhaps not advisable. Various actors, including Adrien Brody and Jackie Gleason, are said to have tried similar diets. The humble egg, once maligned as a heart attack in its own shell, is making a comeback as an aid to dieting. And for all Saatchi’s concerns about cholesterol, it might be more healthy than the buttery comfort of Nigella’s bestselling books.

The writer Fay Weldon, who worked in advertising early in her career, is often credited with creating the campaign: “Go to work on an egg.” Boiled, fried, scrambled – eggs were seen as a good way to start the day.

Then cholesterol and salmonella came crashing down like two giant teaspoons on a shell. Sales fell; eggs came to be seen as unhealthy. The salmonella scare, sparked by the government minister Edwina Currie in 1988, was finally scotched by vaccination. Any egg with the British Lion mark should be safe.

Cholesterol proved stickier. Too many eggs, it was thought, and your blood turned to gooey meringue, transmogrifying your heart into a strawberry pavlova waiting to explode.

“They did a lot of studies in the 1960s when they fed people loads of eggs and measured their cholesterol levels,” said Lucy Egerton (yes, that is her real name) of the British Egg Information Service. “It gave them really raised cholesterol levels.

“But they were feeding them amounts you would never normally eat. Current evidence suggest that blood cholesterol and dietary cholesterol are two different things. You have more effect on your cholesterol level by eating saturated fats, such as pies, butter, cakes and things like that, than from eating eggs.”

More recently, studies in the United States have shown that eggs, which contain protein and vitamins, provide the sort of nutrition that might help control appetite better than carbohydrates.

In one study of obese women, half were fed bagels for breakfast and half eggs, with both groups getting the same calories. The egg-eaters went on to consume less food during the rest of the day than the bagel bunnies.

Egerton points to other advantages too. “People are getting more concerned about whether their food has been processed or tampered with,” she said. “Eggs are just a natural product that comes in its own packaging, and it is portion-controlled, obviously.”

Saatchi wouldn’t give much away about how he likes his eggs. Sunny side up? Poached? With a large helping of ham and chips? He wouldn’t crack.

But if he really did eat nothing but eggs, dieticians have sympathy for his wife.

“After several days you’d get ketosis – carbohydrate deficiency, which is also well-known with the Atkins diet,” said Ursula Arens of the British Dietetic Association. “You get bad breath, constipation, gut problems and sulphurous odours, including eggy burps, over time. And you start to have food fantasies, visions about things you miss.”

Like Nigella’s pineapple upside-down cake? Or her chocolate peanut butter fudge sundae?

Saatchi, who has previously admitted to being worried about his sanity, had it tough. Maybe the only way he could diet was to go utterly cold turkey to stand any chance of succeeding.

Fad diets, such as those based on pineapples, cabbage soup or lemon juice, have an attraction because they take away the need to make decisions. “People find it an easier way to discipline themselves,” said Arens. “When you have little bits of lots of foods it’s easier to lapse.”

Experts, however, are agreed that a balanced diet is by far the better way to achieve lasting weight loss.

“It’s very important to eat a varied, balanced diet,” said Joanne Lunn of the British Nutrition Foundation. “On the ‘eat well’ plate we use to illustrate healthy eating, eggs are present in the group that includes meat and fish.

“But it’s important to eat a dietary pattern that you can sustain in the long term. Otherwise all that will happen is that you will lose the weight, then go back to eating what you’re used to and put it all back on again.”

So stop that butter fudge sundae right there, Nigella. Give the man a chance.

Additional reporting: Christopher Thompson

That’s all yolks — key egg facts

— Britons eat about 10 billion eggs a year – 27m a day.

— Eggs contain protein, vitamin A, vitamin D, niacin and vitamin B12. They also contain about 6.4g of fat, of which 1.8g is saturated fat.

— Four out of 10 eggs sold are free range. In January, for the first time, free-range eggs accounted for more than half the value of all eggs sold.

— In the 1967 film Cool Hand Luke, the lead character, played by Paul Newman, takes on what is regarded as a mad bet to eat 50 eggs in an hour. Truth is stranger than fiction. Sonya Thomas, a Korean-born American, holds the record for eating hard-boiled eggs: 65 in six minutes and 40 seconds. Thomas is slim, fit and weighs about seven stone.

— The record distance for throwing a raw egg without breaking it is 323ft 2in set by Johnie Dell Foley in Texas in 1978. The egg was caught by his cousin, Keith Thomas.

— A typical ostrich egg weighs 3lb 5oz. One laid at a Swedish ostrich farm in 2006 claimed the world record at just over 5.5Ib

— Peter Fabergé, the jeweller, made 50 ornamental eggs for Russian tsars and others for aristocratic private clients. One created in 1902 for the Rothschild family sold last November for £8.9m.

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