Dani Garavelli: When people lose a lot of weight they have to reassess their own identity

So common is the phenomenon that clinics which carry out the procedure hold pre-op counselling sessions to warn their patients of this “side-effect”. Bariatric surgeon Dr John Pilcher claims that, where the partner having the band fitted was already obese at the time the couple met, the chance of a break-up within two years is as high as 80 per cent.

So it is not as shallow as it might sound to suggest the writing was on the wall for lingerie tycoon Michelle Mone’s marriage the moment she started shedding the pounds (albeit using slimming pills as opposed to surgery). The successful businesswoman, who built up her company MJM International with her husband Michael, dropped six dress sizes, regained her self-confidence, appeared on a clutch of reality TV shows and became something of a fixture on the celebrity circuit.

You might have thought this transformation would have been a cause for celebration. But, by her own admission, it wasn’t long before cracks started appearing in her marriage. Michael, used to a partner who was “always there”, found Mone’s newfound zest for life “unnerving”. Although there were benefits – she said their sex life was better and they all ate together as a family – he is said to have had a hard time adjusting to her new, more extrovert personality.

It didn’t help that Mone – whose Ultimo brand has been promoted by models including Rachel Hunter – decided to give her new figure a public airing by doing a photo-shoot in her undies, a move she concedes “appalled” her family, or that she was snapped while out with EastEnders actor Shane Richie and rugby player Gavin Henson. The result is that, although just months ago Mone insisted the couple were working through their problems, their lawyers last week announced an amicable separation.

In a way, it’s easier to understand when dramatic weight loss happens the other way round; when the collapse of a long marriage which has fallen into decline prompts suddenly single men or women to give themselves a much-needed makeover. This is what happened to Vanessa Feltz, who shed four stone after splitting up with Michael Kurer and, Dawn French, who has lost six and a half stone after splitting up with Lenny Henry.

In the same vein, intuition tells us that weight loss should be a boon to an ailing marriage. Where long-term partners have been taking each other for granted, a renewed interest in their appearance ought to give the relationship a new lease of life.

But Mone is not the first woman to discover it can have the opposite effect. Early last year, actress Hannah Waterman split up with her husband, EastEnders star Ricky Groves, after they both lost several stone. And although she denied the split had anything to do with her dieting, the break-up followed a similar pattern to Mone’s. At first the couple were pictured out together looking fabulous. Then both Waterman’s career and social life started gathering momentum; and so it went on until, in January 2010, the couple announced they were to split. In August, Waterman had a baby boy with her new partner, actor Huw Higginson.

According to psychologists, the roots of this phenomenon are complicated. When people lose a lot of weight they have to reassess their own identity, a process which can be unsettling for both partners. If the overweight partner has been obese since childhood, they may experience an urge to sleep around because they feel they were deprived of the opportunity when they were growing up. Or, if a lack of self-esteem has led them to put up with an unhappy or abusive marriage, their weight loss may finally give them the confidence to leave.

Not everyone wants their partner to lose weight; some find fuller figures more attractive, some are born feeders and some enjoy the neediness that a lack of self-esteem brings. Finally, for those who are insecure about their own appearance, going out with someone who turns heads may provoke a sense of jealousy or inadequacy rather than a sense of pride.

Of course, we don’t know the ins and outs of the Mones’ marriage. Although Michelle was candid about the impact her modelling had – “he wouldn’t talk to me for weeks, even now it’s hard to talk about it” – she remained tight-lipped about the separation, merely thanking friends for their support as she announced she was taking a break from Twitter.

However, as we all gear up for the annual detox, it’s food for thought. Would we really pound the streets to burn off the festive fat if the loss of our spare tyre led to the loss of our spouse? Thankfully, as a I devour yet another piece of leftover cheesecake, I realise I have little to worry about. If embracing the role of a human dustbin is what keeps a marriage together then – for the time being at least – mine must be rock solid.