Matthew McConaughey during filming of "Dallas Buyers Club" and after his weight gain.

The 44-year-old actor underwent a crazy transformation for the physically demanding role as aids sufferer Ron Woodroof, shrinking from his ripped beach physique to a gaunt frail frame by losing around 50 pounds.

Surprisingly, the 'Failure to Launch' star admitted that he found returning to his original weight more difficult than dropping it.

The Hollywood star - who is married to Camila Alves - told Hollyscoop: "I gained 45 [pounds] of them back. The gaining was trickier than the losing.

"It's more fun, but it's also trickier. The first big meal that you eat, your body remembers that it lived at 182 pounds and it wants to sprint back and you have to pull the reigns and go, 'Woah! We gotta take it easy.' It's a marathon."

Matthew - who has been receiving critical praise for the role and has received a Golden Globe nomination for Best Actor - was honored with an award for his role in the film at the Palm Springs International Film Festival on Saturday and is already being hotly tipped for an Oscar nomination.

He said of the film's success: "It makes it that much more enjoyable to be here sharing it because we were the underdog from day one. We've been the underdog for 20 years."