Angelina Jolie ''didn't eat much'' on the set of 'Unbroken'.

The 39-year-old actress - who directed the biographical drama about World War II hero, Louis Zamperini - ate like the cast members who played prisoners of war, according to Japanese pop star Miyavi, who plays prison guard, The Bird, in the film.

The 33-year-old singer-turned-actor said: ''She came to the set every day, giving advice to the actors, and she actually didn't eat much [either].

''She was so thin because most of the actors were not able to eat because they're prisoners in the prison camp.''

Miyavi praised his director's ''determination'' and ''professionalism'', revealing that her attitude throughout the filming process was the reason for its success.

He explained: ''She was so determined. I was also surprised how skinny she got. You know, she was not eating much. I felt so bad I was the only one who got fat during filming.

''I really respect her professionalism, her attitude towards the creation - she's so determined and passionate. It was intense on set but with her motivation and attitude we were on the same page.''

Jack O'Connell, 24, who plays the title character also revealed how Angelina would help him and try out all of his stunts first - including a scene where he supports the weight of a heavy wooden plank above his head for hours.

He told RadioTimes.com: ''She did test out all of my stunts before I had to do them. The plank - I'm not sure if that can be regarded as a stunt - but, in any case, she was under it before I turned up on set.''