Traditionally, it isn't over until the fat lady sings. But it seems it will soon be over for the singing fat lady. The stereotypical large woman in a horned helmet and braids belting out Wagner is preparing for her swansong as opera embraces a new, younger audience.
The drive to reach out to these fans is resulting in slimmer, fitter and more glamorous singers on stage. New York's prestigious Metropolitan Opera is in the vanguard of this movement, according to John Allison, editor of Opera magazine. "I have noticed the slimming down of performers," he says, "and I think this is largely driven by the Met, which feels that audiences are more likely to connect with a glamorous, thin singer."
Elaine Padmore, director of opera at London's Royal Opera House (ROH), has also seen a move away from large women to more petite performers in certain roles. "We have been seeing glamorous women and handsome leading men for a time now, but this is the entertainment world, after all," she says. "It is expected these days, when people are used to seeing beautiful people in films and on the television."
Ms Padmore says the trend away from the static style of opera acting to a more dynamic, physical one in which singers move more athletically around the stage is also behind the change.
While it would have been acceptable to audiences in the 1980s to watch a three-hour production of La Bohème with Pavarotti in which the famous tenor would not move at all, those days are now gone. The new crop of performers require a higher level of fitness than before as they dart about the stage.
However, Ms Padmore adds: "Audiences still expect wonderful voices and I don't think they just go to see beautiful people – but it's a bonus if the singer looks like the character."
She insists it is too early to write off the statuesque stereotype; some Wagnerian roles, for example, still demand a "bigger physique". Nevertheless, Marina Poplavskaya and Emma Reed, stars of the ROH's current production of Don Giovanni, are the prima divas among a new crop of svelte performers. Others typifying this new breed include Anna Netrebko and her partner Erwin Schrott, Jonas Kaufmann and Danielle de Niese.
The writing has been on the wall for oversized singers for some time. In 2004, the American soprano Deborah Voight was told that unless she lost weight she was unsuitable for a role in the ROH's production of Ariadne on Naxos. Ms Voight is back in the same ROH production this year, having shed nine stone. "I was not appropriate for the  production," she admitted.
The new formula seems to be working, doing for opera what Vanessa Mae, Anne-Sophie Mutter and Ofra Harnoy have done to boost the profile of classical music. Divas such as Poplavskaya are revitalising ticket sales at the ROH, which has seen audiences surge by more than 10 per cent in the past year. In the financial year to March 2008, the ROH had almost 700,000 people though its doors, some paying up to £210 a ticket, compared with a little over 610,000 the year before. Of these, 26 per cent were between 18 and 35 and earned less than £30,000 a year, evidence that the art form is slowly shedding its elitist mantle.
Some hope the trend towards skinny opera does not go so far as "size zero" singers. "I hope we don't see that," says Mr Allison. "I hope we don't see the end of the phrase 'before the fat lady sings' either, because there are some pieces that require singers to have a huge set of lungs and a big frame to go with it. If glamour and looks are hired before vocal ability, then you are heading for trouble."
Marina Poplavskaya, 30
Russian soprano. Appeared as Tatyana in Tchaikovsky's 'Eugene Onegin' at the Royal Opera House in March and replaced Anna Netrebko as Donna Anna in 'Don Giovanni'. Briefly married to the US bass baritone Robert Hale, with whom she remains friends. Her voice has been described by critics as 'turbocharged'.
Danielle de Niese, 29
US soprano, born in Australia. Appeared as Cleopatra in Handel's 'Giulio Cesare' at Glyndebourne in 2005 and returned there this year in the title role in Monteverdi's 'L'Incoronazione di Poppea'. Seen by some directors as the great hope for connecting with a young audience.
Jonas Kaufmann, 39
German tenor. Appeared as Jose in 'Carmen' at the Royal Opera House in 2006 and as Alfredo in 'La Traviata' at the Metropolitan in New York. Described by critics as the finest tenor his country has produced in 50 years.
Anna Netrebko, 36
Russian soprano. Appeared as Donna Anna in 'Don Giovanni' in 2002 and, last year, as Susanna in 'Le Nozze di Figaro'.
Erwin Schrott, 36
Uruguayan bass baritone who played title role in 'Le Nozze di Figaro'. Has just had a baby boy with his partner Netrebko.
Deborah Voigt, 47
US soprano whose weight, then 25 stone, prevented her playing title role in 'Ariadne on Naxos' in 2004 at the Royal Opera House. Is now 16 stone and has returned to the role.