The cardinals locked away to choose the next pope will be served plain but wholesome food -- and nothing so delicious that they will want to drag out their deliberations, an Italian newspaper reported on its website on Tuesday.

The nuns who will cook for the 115 cardinals during the papal conclave at their Casa Santa Marta residence "are already preparing meals of soup, spaghetti, small meat kebabs and boiled vegetables", the Corriere della Sera reported.

"All of the cardinals consider these dishes as rather forgettable compared to the menus at the restaurants in Rome," the paper added.

"Perhaps this food, similar to that served in hospitals, will help to speed up the choice of a successor," it concluded.

The Canadian cardinal Thomas Christopher Collins joked about the fare on offer at the conclave as he went to a restaurant near the Vatican, the Venerina, two days before the conclave began.

"Make me a nice dish of carbonara," he asked the waiter, referring to the classic Italian spaghetti dish with a cream sauce containing ham and eggs. "Because after the third day of the conclave, if we haven't elected a pope, they'll give us dry bread and water."