In their upcoming film Dallas Buyers Club, Matthew McConaughey and Jared Leto both underwent radical body transformations to play HIV patients, which they discussed with ET.
McConaughey, who plays a drug addict whose life drastically changes when he is diagnosed with HIV and is told he has a month to live, shed nearly 40 pounds for the role, making him nearly unrecognizable with his wiry figure.
PICS: Shocking Movie-Role Body Transformations
Although it was a dramatic physical transformation for him, McConaughey revealed that there was a measured, methodical process behind his major weight loss.
"[It] was just a steady diet. I got with a nutritionist; gave myself four months to do it; lost three pounds a week," he shared. "...Actually it helped me...set a construct for me to focus and do the stuff I needed to do mentally and spiritually with the character."
A year after production, the Texan actor has regained nearly all of the weight he lost and is back up to 175 pounds after hovering around 140 pounds for the role.
VIDEO: McConaughey: Bone-Thin Weight Loss Was 'Spiritual'
While his transformation predominantly consisted of the weight transformation, his co-star Jared Leto had a much more complete transformation portraying a transgendered prostitute in the film who is also HIV-stricken.
"The weight is something that's understandably a topic of conversation. There was also the waxing of the body and the eyebrows, and the wearing of the heels and the eyelashes," said Leto, front man of Thirty Seconds to Mars. "[There was] a lot of physical transformation here, but the inside is, of course, where it really counts."
Even without the necessity of losing weight for his role, Leto was assuming a colossal challenge when he signed on to play the role of a transgendered prostitute. He boldly referred to the role as the "role of a lifetime."
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"I took on this role because I thought it was an incredibly beautifully written script. I thought the role was fantastic; I thought there was tons of opportunity there," the 41-year-old actor and musician said. "This character is so sweet and kind and full of love and humor. I just had to be a part of it. It was the role of a lifetime."
Watch the video above for ET's interviews with McConaughey and Leto, as well as Jennifer Garner, who plays a doctor in the film.
Dallas Buyers Club is in theaters November 1.