Candace (groans): This must be what it feels like to be pregnant.
Candace's medieval counterpart, Candavere, along with her friends Stacehilda and Jenavene, gain some nice bulges after a large banquet at the end of Excaliferb: A Further Adventure.
In Two Lads in Dangrabah, Candace swallows a submarine sandwich whole, which causes her stomach to bulge out significantly. Because in this story, she is a genie, she uses magic to shift the fat in her gut into other places, but since she doesn't do this immediately, it appears that she doesn't seem to mind being bigger.
This is the plot of Queen-Sized Candace, after said character spends a week indulging herself in several desserts, the first meal resulting in Dinner Deformation (which resolves itself after said meal also gives her the hiccups). Later, Stacy and Jenny also get the same treatment.
There is in fact fanart of some of these fanfics, such as the ones here and here, among others.
The Invader Zim fanfic Feast of Doom so far has Zim being fattened up to enormousness for an ally planet's Moon Festival. So much so that GIR gets lost in his rolls of fat.
GIR: I just had the most wonderful adventure...
Sonic the Hedgehog's Rouge the Bat ends up accidentally fattening herself up in Rouge's Weighty Frustrations. She doesn't even notice her weight gain for quite some time, until moments before she decides to go on a heist, where her fat stomach ends up getting her stuck in a small space... twice.
Rouge: Well, this’ll be a red-letter day for the press, won’t it? 'Former Grand Thief, Rouge the Bat, Caught in the Act, Trapped by Her Own Weight'…
This happens to Dawn in the second chapter of the Total Drama fanfiction, Total Drama Prison. She drinks four whole bottles of aged soda as part of a challenge. Not only does her stomach bloat up and start aching, which lasts for the rest of the chapter, but she also gets the hiccups from drinking too much.
The Dragon Ball Z fanfiction Exercise Me focuses on Bulma's weight gain after her pregnancy with Trunks, and how Vegeta reluctantly helps her lose the extra pounds.
Plasma's Folly contains a non-comedic example: assuming his Zekrom form, a famished Ben swiftly devours a platter of food, swallowing whatever he can fit down his throat whole. This is good and fine, until he reverts to his human shape while retaining the contents of his stomach. Nearly leads to Death by Gluttony.