Hollywood hunk Jared Leto says he starved himself for a month to play a transgender woman living with HIV.

The 40-year-old star's new super skinny figure was achieved for his role in the Dallas Buyers Club, co-starring Matthew McConaughey and Jennifer Garner.

The 30 Seconds to Mars band member told entertainment site Vulture that he had to shed the pounds fast because he only got involved with the movie a few weeks ago.

Leto, who also shaved his eyebrows for the part, said: 'Your body goes through weird stages.

'Sometimes it's hard to hold on to water. But for me, it's not about the most weight I can lose, it's more to represent the character. I'm focused on what it means to be a transsexual woman.'

The film is loosely based on the true-life tale of Ron Woodroof, a drug taking, women loving, homophobic man who, in 1986, was diagnosed with HIV/AIDS and given 30 days to live.

Leto will play fellow patient Rayon who joins Woodroof in setting up 'clubs' whose members were supplied with anti-viral drugs unavailable at the time in the US.

'Historically, people have done it [fasting] for pursuit of self, to achieve a meditative state, so I'm hoping for that, and not the other things.' Leto added.

'It's not necessarily a bad thing.'