The episode took six months to make, and was animated entirely out of construction paper.
You can actually see one of the animators left hand come into shot when chef starts singing his song to the boys.
In the pilot (which was edited down to "Cartman Gets an Anal Probe") there is more of Cartman's home life, including a scene at the dinner table where Cartman had at least a father and sister. In the series, Cartman was an only child.
The characters who are not speaking rarely move, saving time in the animation process.
The episode received poor results from test audiences and Comedy Central executives were uncertain whether to order additional episodes of the show. However, as the two original Christmas shorts, "Jesus vs. Frosty" and "Jesus vs. Santa", continued to produce internet buzz, the network paid Trey Parker and Matt Stone to write one more episode. In writing Weight Gain 4000 (1997), the duo sought to give the network an idea of how each episode could differ from the others. The network liked the script and agreed to commit to a series when Parker and Stone said they would not write another individual episode until Comedy Central signed off on a season of at least six episodes.