In Garfield, the title character devours a lot of food even for him, but the shape he gained was more flabby than round.
One strip featured a skinny Garfield bragging that he had finally found a diet that actually worked. He decides to reward himself by eating one single potato chip, which somehow causes him to immediately gain all of the weight back.
Happens on a few occasions to Nemo and Flip in Little Nemo in Slumberland after they eat something unusual.
Red from Red And Rover is known to binge on Halloween candy every few years.
In Peanuts, Snoopy frequently developed one by overeating:
In a 1960s arc, he indulged in dog food in hope of forgetting a failed romance at the outdoor ice skating rink.
In the June 24, 1962 strip, after attempting to mow his lawn by grazing it.
In a shorter 1980s arc, it's stated that he ate 23 hot dogs that Lucy had sold to him during one of their baseball games.
Not to be outdone, Snoopy's brother, Spike, ballooned up in weight when Lucy, who was disgusted with how thin he was, attempted to fatten him up. He was skinny again within a week.
In one storyline in June of 1982, Sally is sent to Beanbag Camp for two weeks, where all the kids do all day is lie around in beanbags, watch tv, and eat junk food. She returns home fat, and revealing that she also signed up for the following summer.
In a storyline in Pearls Before Swine, Rat, angry that the staff at an Old Country Buffet-style restaurant ripped him off, eats the entire buffet's stock out of spite.