Glenn Howerton, Charlie Day, Kaitlin Olson, Danny Devito and Rob McElhenney

Rob McElhenney had just one objective for the new season of It's Always Sunny in Philadelphia, but it was a big one.

"I tried to look as ugly as possible, basically," he said of his remarkable 50-pound weight gain for Season 7. So what exactly compelled the star to transform his alter-ego's normally fit physique into something a little flabbier? "It came when I was watching a very popular sitcom, and I noticed the people were getting better and better looking as the seasons were going on," McElhenney said at the Television Critics Association fall TV previews Saturday. "I always thought that what we were trying to do on Sunny was the deconstruction of the sitcom."

FX orders two more seasons of It's Always Sunny in Philadelphia

After years of making the Paddy's Pub gang as unlikeable as possible —  for example, characters have both become drug addicts to get on welfare and used a baby to score a big Hollywood payday — McElhenney wanted to achieve the same goal through aesthetics. Luckily, the extra pounds are not just a funny sight gag, but also a very believable evolution for the character. "The reality of five people in a dive bar in Philadelphia is that they won't get better abs," said executive producer and star Charlie Day.

And although he wasn't able to convince the rest of his castmates to do the same ("We all said no!" McElhenney's co-star and real-life wife Kaitlin Olson said), McElhenney had some major help in the form of Philadelphia Phillies baseball player Chase Utley. Utley set McElhenney up with a sports nutritionist who also works with offensive linemen in the NFL, and soon the actor was chowing down on 5,000 calories a day for five months.

It may have been a big sacrifice — McElhenney has since shed 20-25 pounds — but it seems it was worthwhile. Day said he feels the show is just hitting its creative peek in Season 7, a sentiment echoed by FX president John Landgraf, who announced Saturday that the network would order two more seasons of the show, with the option open for one more. "We knew, creatively, we're just sort of hitting our stride now," Day said. "Doing those two additional years doesn't feel like we're dragging it through the mud."

Watch full episodes of It's Always Sunny in Philadelphia

In the wake of the cast's recent success outside of the show — particularly Day's role in the surprise hit film Horrible Bosses — many wondered if the curtain would close for good this year. However, Day said because the show has largely been able to stay "underground," they felt there was an appetite for more. "If we were seven years into an overhyped television show, we would probably be as sick of it as the public," Day said. "There's no reason not to keeping making it if people still enjoy it."

The new season of It's Always Sunny in Philadelphia premieres on Thursday, Sept. 15 at 10/9c on FX.

Watch a preview with "Fat Mac:"