She has indulged in on-stage lesbian kisses, raunchy music videos and erotic books.

But Madonna has revealed that her attempts to seduce husband Guy Ritchie were once defeated – by biscuits.

The pop icon – who last week gushed about her "incredible" love life – says her film director husband went off sex while trying to lose weight on Hollywood's latest craze, the Cookie Diet.

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Madonna and Guy Ritchie have been dogged by rumours that their marriage is in crisis

It involved the Lock, Stock And Two Smoking Barrels director eating up to four biscuits instead of breakfast and lunch, but his 49-year-old wife was disappointed by the effects.

Fortunately for the Like A Virgin singer, Ritchie, 39, is now back to eating normally.

Followers of the diet, including singer Kelly Clarkson and Oscar-winner Jennifer Hudson, eat 800 calories a day for three weeks.

Madonna told an American radio station yesterday: "My husband went on that Cookie Diet and it was such a turn-off because he didn't want to have sex. He's not on it at the moment, thank God.

"He did [lose weight] but he didn't really need to lose that much weight. I think he did it because all his friends were doing it and he wanted to see if he could do it."

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The singer shows off her lean physique in her latest video 4 Minutes

Her sex-life confession is at odds with a tribute to Ritchie on her forthcoming album Hard Candy in a song called Incredible.

In a magazine interview, she said: "Sex with Guy is incredible...and, surprise, surprise, it's his favourite song on the album. Actually, maybe it's not his favourite song but it's definitely his favourite line."

The singer has made sex the centre of her public image ever since her first No 1 hit, Like A Virgin, in 1984. Since then, she has published a book of erotic photographs of herself called Sex, had the explicit video for Justify My Love banned by MTV in 1990 and kissed Britney Spears and Christina Aguilera at a music awards ceremony in 2003.

In recent months, however, Madonna has been dogged by rumours that her marriage is in crisis. Last month, the couple were forced to issue a statement denying a split, which read: "Mr and Mrs Guy Ritchie remain happily married."

She said: "I had to marry a challenge because otherwise I would just get bored. Whatever else Guy is, he's never boring... We're both there to help each other and challenge each other."

But she added that she was the one left to tell off their children, Lourdes, 11, Rocco, seven, and David, two.

"Guy's a softie with our kids," she said. "Lola [Lourdes] rules the roost. She is extremely maternal towards David. He is the apple of everyone's eye."

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Madonna says daughter Lourdes, 11, 'rules the roost' in the house