The 43-year-old actor, known for a muscular physique, lost 38 pounds in order to play the role of Ron Woodroof, a man diagnosed with AIDS in 1986. The film also stars Jennifer Garner and Jared Leto.
As McConaughey arrived in New Orleans earlier this week to begin filming, many were alarmed at his frail and gaunt frame. He spoke with HitFix about his weight loss process that took just five weeks.
"I feel good now," he told HitFix, which noted the actor looks very different than he did when they interviewed in June.
"Overall, [I] probably got 35 percent less energy. But the tough part is there have been plateaus. Getting past 170 was really hard, but then once you get 167, the next seven come off easy. Getting past 160, really hard, but then you fly down to 150. Getting past 150 was really hard and then, bam! 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."
McConaughey did not get into details about his exact weight loss diet, but he did admit that he had to change his eating habits drastically in order to beat those plateaus.
"I'm doing cardio but I'll tell you what, the more I've learned is — and I think it comes with age, too — is it's 90 percent diet," he explained.
"It's 90 percent amount and then what you're eating because right now I'm not losing any more weight if I burn 1,500 calories — two hours of cardio in an afternoon — or if I don't. It doesn't matter. It's a matter of how much I eat or how little I eat."
The actor says he is looking forward to being able to eat normally again, but he is aware that may not include fatty foods as quickly as he would like.
"The organs shrink, so my stomach has shrunk as well," he says. "So as much as I can't wait to have that cheeseburger, on that day, it'll be damn hard to eat the whole thing," he said.
McConaughey has a detailed preparation plan for that first burger.
"I will have some 70 percent beef, 30 percent fat ground beef, maybe a half pound cheeseburger with another three types of cheese," he said.
"I'll prepare it all [myself] and I'll make sure that it takes three hours just to prepare. I'm going to have buns with butter on both sides, toasted and grilled. I'm going to melt the cheese on the top bun [and add] Hellmann's Real Mayonnaise. I want kosher dill pickles sliced nice and thin, diced white onions, slightly grilled until they get almost hard, and some thin jalapeno slices. And then I'm just going to sit back and let the [expletive] just drop on the ground."
"The Dallas Buyers Club" is scheduled for release in 2013.