Scarlett admits catsuit diet secret

Scarlett Johansson has revealed she had to switch to a high vegetable diet to fit into her Black Widow catsuit.

The 27-year-old reprises her role as Russian spy Natasha Romanoff, whose alter-ego is the feisty superhero, in Joss Whedon's Avengers Assemble.

She admitted she had to change her food regime to slip into the unforgiving outfit, during a press conference in London with her co-stars in the action film.

"How come I get the rabbit food question? Yes, surely. You're training and doing all that stunt work so you eat a lot of green things," she said.

Scarlett - who previously portrayed the heroine in Iron Man 2 - did a lot of training alongside Mark Ruffalo (Bruce Banner/Hulk) and Tom Hiddleston (Loki) to prepare for the role.

"I think me, (Jeremy) Renner and Tom probably spent the most amount of time in the stunt gym, because we have these huge, intense choreographed sequences," she admitted.

"I'm happy to do that. It's great fun to do it. We all have our burden to bear, but certainly the stunts paid off in the end."

The actress admitted she had no hesitation about getting involved in Avengers Assemble, which sees Marvel superheroes - Iron Man (Robert Downey Jr), Hulk (Mark), Captain America (Chris Evans), Thor (Chris Hemsworth) and Hawkeye (Jeremy) - joining forces to battle against villain Loki.

"When I first met Joss, he talked to us individually to see what we wanted for our characters. Joss is gender-blind in some way: he wants his female characters to be dynamic, competitive, assured and confident and that has nothing to do with anything but the fact that he celebrates those kinds of strong female characters," Scarlett added.

Avengers Assemble opens in cinemas next Thursday, April 26.