Matthew McConaughey went on a 10-day fast after filming 'Gold'.

Matthew McConaughey

Matthew McConaughey

The 47-year-old actor was able to relax his workout regime and piled on nearly 50lbs pounds to play prospector Kenny Wells in the new movie and while he had fun gaining weight, he found slimming down afterwards much harder and had to take drastic measures to shock his body.

He said: "Putting it on was easier and fun - cheeseburgers, beer, whatever I wanted.

"Taking it off, I did a 10-day fast just to kick-start my body into saying, 'Oh we're going without!'"

Matthew - who famously lost almost 40lbs for his Oscar-winning performance in 'Dallas Buyers Club' - admits Kenny is his "favourite character" he's ever played, but his mother didn't share his enthusiasm.

He told 'Entertainment Tonight': "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 favourite character I've ever played.

"[My mom] 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.' "

But the hunky actor's kids, eight-year-old Levi, seven-year-old Vida and four-year-old Livingston - who he has with wife Camila Alves - loved having "Captain Fun" for a father during filming in Thailand.

He said: "It was a wonderful ride. They were very happy. I was very happy with you know the Kenny Wells part of me that I brought home.

"My nickname was Captain Fun for six months 'cause I was yes to pizza night, even if it was Tuesday morning. I was yes to going to the carnival at midnight on a school night. I was like yes, yes, yes."

And the 'Lincoln Lawyer' star admits he wouldn't be able to give his all to his career if it weren't for the support of his wife.

He said: "You do all this work and people see it, and when they see it, they think you made it last week.

"But some of us have been a part of it for five years. We picked up the family, uprooted everything, went to Thailand, did it, they came with me.

"I have a wife that thankfully tells me when I go to work, 'Don't look in the rearview mirror. Go do your work, get obsessed with that. I got it. I got your back.' So it makes the whole process so much more enjoyable for me."