Matthew McConaughey and wife Camila Alves attend the Andy Roddick Foundation Gala held at the W Hotel in Austin, Texas, Sept. 21, 2012 (Arnold Wells/WENN.COM)

Actor Matthew McConaughey's drastic weightloss has left him sore all over his body, but he insists he's "as healthy as can be".

The usually buff Magic Mike star has shed 40 pounds to play a skeletal AIDS victim in his latest movie The Dallas Buyer's Club, and his emaciated frame has given some fans cause for concern.

McConaughey is adamant his extreme dieting isn't doing any real harm to his health, and he is relying on a diet of fish to keep his energy up.

He tells TheDailyBeast.com, "I feel fine. I really do. I'm eating fresh fish. I'm just eating small amounts. I'm not being starved. If anything, it's as much a spiritual journey as it is physical.

"I have body soreness. (But) I'm as healthy as can be. My blood pressure, everything's fine."

McConaughey previously revealed he was dreaming of sinking his teeth into a greasy cheeseburger once filming on the drama ends, but he now accepts he won't be able to devour the meaty treat straight away.

He explains, "You can't just start eating cheeseburgers and ice cream. Your body will go into shock."

Meanwhile, McConaughey's co-star Jared Leto has assured his devotees he is happy and healthy after shedding a few pounds himself to play an HIV-positive cross dresser in the film.

In a post on Twitter.com on Thursday, the rocker/actor writes, "Thanks for all the concern.. energy a bit low but I'm doing ok over here!"

Leto was also forced to wax off his body hair and have his eyebrows plucked for the part.