From the comic's website:

Q. Where do you get your story ideas?
A. I get the funniest ideas from my friends and especially my family. My daughter, at the age of six, announced at dinner that she could no longer eat chicken because she's a vegetarian. My wife told her that she'd have to start eating vegetables, because that's what vegetarians do. My daughter said something so funny, I used it in a strip without changing a word. She said, "I do eat vegetables. I eat macaroni and cheese."