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Matthew McConaughey was bursting at the seams—literally—while filming Gold.

The 47-year-old Oscar winner transformed his appearance to play gold prospector Kenny Wells, adding 47 lbs. to his typically athletic frame. McConaughey shaved his head and wore a toupee, and he worked with hair and makeup artist Felicity Bowring on a set of veneers.

Directed by Stephen Gaghan, Gold—co-starring Bryce Dallas Howard, Toby Kebbell, Craig T. Nelson, Édgar Ramírez, Corey Stoll and Rachel Taylor—arrives in theaters nationwide Jan. 27.

Gold, Matthew McConaughey, Bryce Dallas Howard

The Weinstein Company

McConaughey famously lost 38 lbs. for Dallas Buyers Club, but Gold marked the first time he'd ever gained weight for a role without adding muscle mass. "I haven't ever done that. I said, 'McConaughey, you have six months to say yes to whatever you want to eat and whatever you want to drink. Whenever.' That was fun," he says. "The only thing that gets tiring is the thought of quitting. It was fortunate that I was like, 'Oh, this is also my job, so let's go—all green lights.'"

Surprisingly, packing on the pounds was much easier than he'd anticipated.

"My favorite food is cheeseburgers, so I was eating cheeseburgers all the time. I was making cheeseburgers. I was trying out all these fast food restaurants that I've never had, or I've only had one time," he explains. "Not that much sweets. Cheeseburgers and beer will do the trick."

Gold, Matthew McConaughey, Bryce Dallas Howard, Edgar Ramirez, Corey Stoll

The Weinstein Company

Gold, Matthew McConaughey, Bryce Dallas Howard, Edgar Ramirez

The Weinstein Company

In addition to eating "whatever I wanted," McConaughey stopped working out altogether. "I wouldn't even take the stairs to the second floor," he says. "That would be too much exercise."

McConaughey's three children with wife Camila Alves "loved" their dad's gluttonous phase. "I was Captain Fun—that was my nickname around the house, because I was [saying] 'yes' to everything," he tells E! News exclusively. "I was a really fun dad for that six months because I was like, 'No, pizza night's not just Friday night—it's Tuesday night; it's Wednesday morning.'"

After production wrapped, it was time to lose weight. "It was somewhat daunting. I had to be patient. I looked at myself like, 'This is not going to happen overnight. This isn't going to happen in a couple or a few months.' I still have a couple things back here that feel like they're renting to own," he jokes. "Whatever your normal weight is, your body wants to go back there, or go up there, and find that place again. The hard part was getting down to...I would go from 217 to 211, easy. Then 211 to 209, crossing that 210 mark was really tough. Then go 209 to 201, easy."

For more from McConaughey, watch E! News tonight at 7 and 11, only on E!.