Opera usually involves the suspension of disbelief, but in the case of Deborah Voigt it needed quite a lot more than usual. As the world now knows, she is the soprano who was deemed too fat even for Covent Garden. For years audiences and directors had put up with the truly gargantuan singer, who tipped the scales at about 25 stone at her zenith.

The assumption was that her creamy, voluptuous voice (known in the opera world as a dramatic soprano) would carry the day, and it usually did. Until the Royal Opera House decided to pull the plug, publicly and abruptly releasing Voigt from her contract to sing the title role in Richard Strauss’s Ariadne auf Naxos, and replacing her with a slim-mer model.

The reason for her sacking was that she could not fit into the slinky black evening dress required by the production. Cue international outrage, typified by a bony woman on Good Morning America, who disingenuously interviewed Voigt as if the diva were a curvy size 14, not a dangerously overweight size 30.

Four years later Voigt, 47, is finally back at Covent Garden – indeed, she is singing Ariadne in the same production, but this time she is nine stone lighter. Yes, the furore was humiliating; yes, it was public; but she has calmed down somewhat. “I was not appropriate for the production,” she admits now.

Furthermore, the sacking gave her an unexpected window of free time, plus a big, fat cheque from the (publicly subsidised) opera house. So she filled the gap in her schedule and used British taxpayers’ money to undergo a gastric bypass operation.

Privately, she was desperate. Forget all that guff about the glories of fat operatic dames: Voigt had had enough of waddling through the great roles.

“I didn’t need the Royal Opera House to tell me I was obese,” she says. “I don’t like to say how much I weighed at the time, but I was well over 300lb [21st 6lb]. I had enough energy to get through a performance, but not enough to get through the next day.

“I was fatigued walking across the street. I was winded walking upstairs. The irony is that I had already made inquiries with doctors. And so, because the opera house honoured its contract, we could say Covent Garden paid for [the operation].”

It was the final salvo in a battle with her weight that had been going on since she was a child. She had tried numerous diets; she had tried drugs (losing five stone with the controversial fen-phen dieting drug before it was withdrawn); and she’d had operations before. When she was 23 she had a “gastric bubble” inserted – an inflated balloon that takes up so much room in the stomach that little space is left for food. It wasn’t a success: the bubble deflated and had to be removed. In any case, Voigt had already subverted its effectiveness by the simple technique of “eating half a candy bar rather than the whole candy bar”.

Gastric bypasses, on the other hand, don’t allow you to continue with your bad habits. “You can’t tolerate sugar at first, so you have to comply and eat protein,” she explains.

Deborah Voigt grew up in Illinois and started choral singing in church and at school. Her two brothers did all the sporty stuff; Debbie was the musician of the family, and so her place was indoors. And weight was always an issue.

“My mother struggled with her weight for years, but she was not obese. When I was maybe 14 I started to put weight on; but when I look back at photos, I was just curvaceous. I was a voluptuous girl: I had full hips, full breasts and full thighs, but a narrow waist and arms.

“When you are surrounded by girls who are lean, and in a family which was aware of weight, it’s not surprising my mother and I were dieting constantly. But it would have been better had I been encouraged to get off the piano bench and ride a bike.”

Her father, in particular, turned the consumption of food into a battle-ground. “His mother was very heavy, and so he was very weight-conscious.

The message that was sent was one of ‘Be careful – watch what you eat’, rather than ‘You are beautiful; why don’t we go on a walk together?’.”

It was an old-fashioned approach, which eventually backfired. “Parents today have a clearer understanding of messages they are sending to their children, but at the time it wasn’t so clear,” Voigt says. “They thought it was better to tell me I was getting fat, rather than thinking, ‘What is going on emotionally with this girl that is causing her to sneak cookies from the cookie jar?’ ” Eating for solace led to food addiction, which the peripatetic nature of her profession does little to quell. “You eat because you are happy, because you are sad, because you are travelling alone 10 months of the year, because you have an entire evening to kill and because a salad is not as fulfilling as a plate of chips.”

The knowledge that chips are a bad food option, which might stop most people from devouring a plateful, has no effect on her, she says. “I have a guilt mechanism, but that kicks in after I’ve eaten them, not before. Mine is a compulsion to eat. So I will have the chips, or the extra glass of wine, and then feel guilty about it.

“What I am working on, and will work on for the rest of my life, is developing a memory of that guilt. I don’t stop and think, ‘How will I feel after-wards?’ I just think, ‘I am going to satisfy myself. I am going to eat this and enjoy it, and it will make me feel better.’ And it’s very hard to break that pattern.”

The gastric bypass, she says, was “the best means to an end. But it was the last means to an end as well”.

Wasn’t she terrified about the operation itself, which can be perilous? Indeed, only last week the papers reported the death of Suzanne Murphy, a Briton who weighed 19 stone and died four days after a gastric bypass operation. Traces of the super-bug MRSA were found during a postmortem examination, but the doctors said her “morbid obesity” was likely to have contributed to her death.

“I have a very strong faith and I knew that God was not going to let me die on the operating table,” Voigt says.

All right, but did she have any fears about what the reduction of her giant frame might mean for her giant voice – a honey-hued monster capable of soaring over Wagnerian-size orchestras and through cavernous auditoriums?

“Yes, of course I was worried. Because when you have extra weight, all you do is take a breath and it automatically supports your body, and the sound comes flying out.”

And, indeed, one thinks of those giant divas of the past: Schwarzkopf; Sutherland – magnificent women with a stately embonpoint like a mantelpiece on which you could park a cup of tea. “Those ladies were big by nature,” Voigt says calmly. “They had big busts, big jaws, big resonating craniums – but they were not carrying 50lb of weight around their middles.

That’s the difference.”

How about the old saw about being proud to be fat? For many years Voigt herself banged this drum; indeed, she was a totem for every size 18-plus opera fan. “When I had that attitude, it was more of a defence mechanism,” she says. “And in terms of health it was a foolish mantle to carry. It’s one thing being 50lb overweight. But more than 100lb? That’s a serious health risk.”

Furthermore, Voigt’s decision was underpinned by commercial concerns. “Opera has to compete for entertainment dollars like anything else,” she says. “People look at magazines and see the ideal representation of beauty; they have difficulty suspending that when they go to the opera. No matter what they are hearing.”

That is particularly true when surtitles are giving an incongruous commentary. “When you are seeing a 22-stone woman singing beneath surtitles which read ‘the most beautiful woman in the world’, that is not believable,” Voigt says dryly. “No matter what your face looks like, from 3,000 seats away all the audience sees is this woman heaving herself across the stage.”

Indeed, at one point in the current production of Ariadne, Voigt not only sings, “I am a thing of beauty”, but also informs us that she is so light on her feet that she doesn’t even trouble the grass when walking. Not a big problem to get away with that when you are an elegant size 14; pretty tricky when you are elephantine.

Most of the critics are satisfied that her voice has kept its former power, and she can certainly do more now than stand in a tent and wave her arms about. In fact, there’s a whole new range of repertoire available to her. Characters such as Tosca – “women who are beauty girls, full of temperament and drama”, as she puts it – are now within her range.

That said, she’s not fooling herself. “The gastric bypass is a tool; it’s not a cure,” Voigt says. “I am addicted to food, and always will be. I’ve just put on about 15lb [more than a stone], and it’s driving me nuts. I’d like to be a size 10 or 12, not a 14 to 16, but I have to be realistic. I am a Wagnerian soprano and I’m not meant to look like a ballet dancer. So it’s all relative, but it’s hard to keep that clear in your head.”

She’s also phlegmatic about the fact that she will always be known as the woman who was too strapping for Strauss. “Do I want to be for ever listed in the opera books as the girl who was fired for not fitting into a little black dress? I’d rather be remembered for my Tristan and Isolde. That will happen as well – I’m confident about that.”

She’s not, however, unhappy to be known as a former fat lady who’s still addicted to food. Now that it’s all out in the open, Voigt knows she is in a position to help others out of the same morass. “I’m frightened when I see obese children aged eight, nine or 10 lining up at McDonald’s for lunch. It terrifies me. The Royal Opera House situation is over, but the greater picture is that I have had this experience – so how can I use it to bring aware-ness to the issue?”

And, what the hell – the publicity hasn’t done her career any harm. “My old publicist Herbert Breslin always said we needed a good scandal. Ha! He was absolutely right.”

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