The Secret Behind Mac's Massive Weight Gain On It's Always Sunny In Philadelphia

Sure, one of the many rewards of watching "It's Always Sunny in Philadelphia" has been seeing jokes like Charlie Kelly's (Charlie Day) knowledge of "bird law," and the degradation of Cricket (Dave Hornsby), become ridiculous running gags since the show's premiere in 2005. What also makes the dark sitcom worth viewing from the start is how all of the gang's antisocial and selfish behavior only gets worse as the years go by. Dennis Reynolds (Glenn Howerton) is eventually implied to be a murderer, Dee Reynolds (Kaitlin Olson), much like her twin brother, declares herself "a Golden Goddess" in a recent season, and Frank Reynolds (Danny DeVito) happily lives an increasingly sleazy, dirty lifestyle bonded to the illiterate and strange Charlie.

Ronald "Mac" MacDonald (Rob McElhenney) arguably goes through the most changes of the main cast because of his need to be liked, as well as the insecure Philly resident's body dysmorphia and complete denial about his sexuality. Mac makes some unhealthy, radical fluctuations in weight, but, in a surprisingly positive step for an "It's Always Sunny" character, at last comes out as gay in Season 12.

McElhenney took on different regimens to draw laughs from Mac's absurd body transformations, but it wasn't easy. This is what the actor had to do every time he decided Mac should take on a new look.

Rob McElhenney told The AV Club in 2011 that he was inspired to make Mac gain 50 pounds for Season 7 of "It's Always Sunny" because of shows like "Friends" and "The Big Bang Theory." The actor and show creator noticed that as the characters got older, the ensemble cast members had more makeup on and looked better. "If anything, when you're in your late 20s, early 30s, and then mid-30s, you're getting less attractive," he joked.

McElhenney decided to write an arc where Mac believed he'd "gained mass" and now looked truly intimidating but, ever in denial, he'd merely put on an unhealthy amount of weight. The intent wasn't to make fun of overweight people but to mock Mac's absurd body image: "It was more about the character specifically."

To gain the weight for the episodes, McElhenney had to eat five 1,000 calorie meals a day. At first, this meant proteins like chicken breasts and vegetables. But as he confessed to actor Nick Kroll, he eventually started eating Big Macs and donuts instead (via The Wrap). It was a fun diet apparently, as he said, "I never felt lethargic. I felt great."

McElhenney went on a diet and was back to his standard size by Season 8, but he wasn't done using his body as a comedy prop. The next effort would be much more difficult however.

For Season 13, McElhenney once again underwent a special diet to play a whole new Mac, in part as a comment on the massive transformations in muscle and shape young actors will now go through for roles. McElhenney thought it would be hilarious if, unlike those movies and shows, "you show it off for essentially 45 seconds in one scene, and the [other] characters are not impressed. They tell you to put your shirt on. That seemed funny to me" (via Men's Journal). 

Mac's actor really did put months of effort into the gag too. He wisecracked via an Instagram post, "Look, it's not that hard," then listed his grueling workout and diet routines, which included avoiding any carbs or sugar, lifting weights six days a week, and three mile runs every day.

These may seem like radical changes as a performer for the sake of a few jokes, but McElhenney's intent with "It's Always Sunny" was always to go for extremes and for what felt funny to his sensibilities, even if it was shocking. As he told The AV Club, "We just try to find a comedic side to darker situations and hope that other people, you know, come along for the ride."