Scarlett Johansson reveals catsuit diet secret

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

The actress plays Russian spy Natasha Romanoff, whose alter-ego is the feisty superhero, in Joss Whedon's Avengers Assemble.

Johansson admitted that she had to change her food regime to slip into the unforgiving outfit, during a press conference ahead of the film's UK premiere in London.

"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," the 27-year-old said.

To prepare for the role, Johansson, who previously played the heroine in Iron Man 2, trained alongside Mark Ruffalo (Bruce Banner/Hulk) and Tom Hiddleston (Loki).

"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.

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

"I was working with actors who I've admired for a long time and you always hope you can do one film with them, and then suddenly, you find yourself working with all of them. It's pretty surreal," she added.

The film opens in cinemas on Thursday April 26 and fans will also be able to see Samuel L. Jackson, Gwyneth Paltrow and Clark Gregg, who complete a star-studded cast.