Matthew McConaughey is used to losing weight for movies -- including the 38 pounds he lost for his Oscar-winning role in "Dallas Buyers Club" -- but "Gold" marked the first time he had to gain weight without also gaining muscle.

You may think gaining weight is easier than losing weight ... and you'd be right! It's also more fun.

McConaughey told E! News he was "Captain Fun" around his house during the six months he worked to gain 47 pounds; his kids loved it because Dad said yes to everything they wanted to eat, making pizza night every night -- and morning.

"My favorite food is cheeseburgers, so I was eating cheeseburgers all the time," McConaughey told E!. "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. Not that much sweets. Cheeseburgers and beer will do the trick."

He also stopped exercising, which makes sense if you want to gain weight without muscle.

"I wouldn't even take the stairs to the second floor. That would be too much exercise."

It's a gluttony and sloth dream come true, but what happens when it's time to lose the weight? Well, McConaughey's genes helped him out there, since his body -- even at age 47 -- seems to want to be lean and lanky.

"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."

But it still took patience, and he still feels like he's not quite back to how he was yet.

McConaughey told Entertainment Tonight his mom had a strong reaction to the transformation.

"She kind of said, 'Matthew, what... oh jeez... well... I like it better than when you were really, really skinny. Golly. You look like your dad. OK, I guess you gotta do what you gotta do.'"

To play gold prospector Kenny Wells, McC not only gained weight, he shaved his head, wore a toupee, and wore a set of veneers. But he loved it, and he told ET he loves the character:

"Kenny Wells' indulgences work for six months and then I had to come back and tighten up a little bit, but he's a wonderful character. A wonderful American archetype. He's my favorite character I've ever played."

"Gold" will be released wide on January 27.

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