This Is What Rob McElhenney Ate To Gain Weight As 'Fat Mac' For ‘It’s Always Sunny In Philadelphia’

He went from 'Fat Mac' to 'Jacked Mac', and now the star has revealed the disgusting diet he went on to pack on the pounds for his role.

Speaking to Dax Shepard in a recent episode of the podcast Armchair Expert with Dax Shepard, the actor revealed the nauseating diet he undertook in order to gain nearly 30kg in just three months.

But first, here's the backstory behind the actor's decision for his character to gain weight for the show:

Prior to Always Sunny's 2011 season, McElhenney was editing an episode, where he noticed an unflattering angle, he had him thinking, “That’s not a good angle of me.”

It was this thought, however, that gave the star an idea -- that everyone on the show look as disgusting as possible so that it would be more realistic, seeing as their characters are generally pretty disgusting people.

He then spoke to the rest of the cast, suggesting that they all gain 60 lbs (22kg) -- and most of them refused. “DeVito is the only one that agreed, and I was like, ‘No. Not you. You’ll die,'” he said, adding that he asked the actors if they were happy for him to do it. “Sure,” they said.

Image: FX

Turns out, Rob revealed, that gaining a massive amount of weight in three months isn't actually as easy as it seems.

After attempting to gain the weight “healthy” on the advice of a nutritionist -- a diet which saw him load up on chicken breasts, rice and vegetables -- the 41-year-old said that it "didn't work."

“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.'” After inquiring what the healthiest way to pack on the pounds, the nutritionist said he could eat a lot of chicken and vegetables and rice, or he could eat two Big Macs.

"So, I said let’s start doing that [eating 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 [melted ice cream] in the afternoon. I was also drinking [wine] heavily.”

“But this was the key,” McElhenney added. “I read that cottage cheese metabolises 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 metabolises 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 [72 kg] to 220 [99 kg].”

And while he says his blood pressure remained stable throughout the diet, he “gained a fatty liver.” However, as he stopped drinking the issue soon fixed itself.

"Losing weight was easy because I was drinking probably 3,800 to 4,000 calories a day and when I stopped, I lost all the weight,” he added.

As for turning himself into "jacked Mac," he says, “Look, it’s not that hard. All you need to do is lift weights six days a week, stop drinking alcohol, don’t eat anything after 7 p.m., don’t eat any carbs or sugar at all, in fact just don’t eat anything you like, get the personal trainer from Magic Mike, sleep nine hours a night, run three miles a day, and have a studio pay for the whole thing over a six to seven month span. I don’t know why everyone’s not doing this. It’s a super realistic lifestyle and an appropriate body image to compare oneself to.”

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Image: FX