Jared Leto is hoping to achieve a ''meditative state'' by fasting.

The 40-year-old singer-and-actor was cast as a transsexual woman in new movie 'Dallas Buyer's Club' - for which co-star Matthew Mcconaughey has dramatically lost a huge amount of weight - and is taking his diet to the extreme to look right for the role, though he admits it has sparked some ''weird'' effects on his body.

He told website Vulture: ''I'm playing a transsexual woman. I didn't get involved in the project until three and a half weeks ago. Your body goes through weird stages (when fasting). 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.

''Historically, people have done it for pursuit of self, to achieve a meditative state, so I'm hoping for that, and not the other things. It's not necessarily a bad thing.''

Jared's co-star Matthew is playing real life AIDS victim Ron Woodroof in the upcoming film and he had to shed 38lbs for the role.

Matthew recently admitted the extreme diet he had to undertake had a huge impact on his energy levels.

He said: ''Overall, [I've] probably got 35 per cent less energy, but there's been plateaus. Getting past 170 was really hard, but then once you get [to] 167 the next seven come off easy.

''Got down to 143 and that's where I want to be. So, once you get past the plateau, your body seems to understand, 'OK, this is where we're leaving now, this is where we are' and so the energy rises.''

Woodroof was given six months to live after contracting the disease in 1986 and he ended up spending the next six years smuggling unapproved medicine into the US to help himself and fellow sufferers. He eventually died in 1992.