When people talk about the incredible transformations that the likes of Christian Bale goes through for roles, Rob McElhenney's transformation for 'It's Always Sunny...' needs to mentioned in the same breath.

McElhenney was on Dax Shepard's 'Armchair Expert' podcast this week and, sure enough, the comedic actor's incredible commitment came up and how he managed to balloon in weight and then drop it just as easily for the show.

While he's been open about the fact that he went through a huge amount of training and dieting to get in shape for his uber-ripped persona, Fat Mac was a different story altogether.

As he told Shepard, he even went to a doctor for advice on how to gain weight without damaging himself. As it turns out, it wasn't that simple. "So, I went to my doctor, because I wanted to be monitored through the whole thing, because this is funny. And my doctor said, 'To be clear, this is not funny. Don’t do this. This is really dangerous.'"

It didn't stop him, however, as McElhenney explained that the jumping-off point was two Big Macs a day. "So, then I had Krispy Kreme donuts. Every morning, I would have four of those and by the afternoon, I was drinking ice cream. I would take ice cream, and I would put it out on the counter in the morning and it would melt and I would put weight gainer in it, and I would drink it in the afternoon. I was also drinking (wine) heavily."

The real trick, he said, wasn't just all of this - it was eating cottage cheese.

"I read that cottage cheese metabolizes really slow in your stomach, so if you eat cottage cheese, the last thing you want to do is eat it right before you go to bed because it metabolizes so slowly. So, that’s what I decided I had to do. So, I started eating cottage cheese in the middle of the night. I would wake up at 2 a.m. and I would eat cottage cheese. One week after that, I came in on a Monday and for whatever reason, it was like I popped."

"I went from 160 to 220 (pounds)," McElhenney added. That's right, he jumped a total of 60 pounds, all in the space of about three months. 60 pounds is nearly 30 kilograms, or 4 stone.

For a joke. What the actual f*ck. You can listen to the full podcast here.