Heavy Voice

A character gains a lot of weight in a short time, gaining mass in every part of their body, even their voice. Their voice will get deeper and thicker as if some of the extra pounds ended up in their larynx. Generally only found in animated works, and very common in anime. Not to be confused with the Heavy's voice.

Anime and Manga

 * Lampshaded by Hachibei in chapter 88, page 14 of Ai Kora when he tells Kirino, after she has gained weight due to a drug slipped into the dorm's water supply, that her "voice is fatter". This is a pun in the original Japanese version of the manga, in which Hachibei tells Kirino "koefuto", which can usually mean "to grow fat", but in this context it includes the word "koe" meaning "voice".
 * In episode six of Wandaba Style, The Professor is in a slump, so his pilots (the girls of Mix Juice), have nothing to do, and thus gain weight from just sitting around. This is hinted at (before we see them completely) by their voices. (Note: averted in the English dub)
 * In an episode of Wagamama Fairy Mirumo De Pon!, Mirumo and Kaede both gain weight thanks to Kaede's rival sending her cakes. Kaede doesn't gain too much weight, but Mirumo, being a Lilliputian, has a more substantial weight gain with a lowered voice to match.
 * During an episode of MAR, the team (specifically, Princess Snow) fights against an ugly little girl whose signature ARM is the Gingerbread House - a house of sweets. Eating it makes her grow to sumo-like proportions, gaining superhuman strength and toughness in the process. And of course, as she grows bigger, her voice grows deeper and thicker. (Also, she turns into a Gonk.)
 * In the seventh episode of Di Gi Charat, Gema falls in the river and drinks a lot of water, making him grow huge and giving him a deep voice.
 * Zura from Mamotte Lollipop is a little seahorse-thing that can blow up like a balloon and float. When it does this, it can still talk, but its voice is much deeper than usual.
 * This happened to Stocking in episode 4-A, after she balloons into an obese giant.
 * Samurai Champloo's Fuu gets this whenever she gorges herself in at least the Japanese and English versions of the show (not so much in the German version).
 * One Piece, Usopp on the Bowin Islands.

Film

 * Inverted in The Nutty Professor, in which the obese Sherman Klump gets a lighter voice as his skinnier alter-ego Buddy Love.

Live-Action TV

 * After The Daily Show came back from a 3-week hiatus in September 2009, Jon Stewart ended up like this.
 * In Super Sentai (less often in Power Rangers) the Monster of the Week often gets a deepened voice after Make My Monster Grow time.

Video Games

 * In Super Smash Bros Brawl, when a characters gets a mushroom and grows larger, their voice deepens. Justified in that the mushroom doubles the size of their entire body, including the voicebox.
 * In the Uncharted series, the Doughnut Drake costume makes Nathan very, very fat. As a side-effect, his voice is pitch-shifted downward by about 15%.
 * In Mario and Luigi Bowsers Inside Story, the Toads infected by the blorbs have deeper speech vocalizations than those who are uninfected.
 * In Sly 3: Honor Among Thieves, when Carmelita Fox is wearing the Mask of Dark Earth, her voice gets deeper as she gets larger.
 * As the titular princesses of Fat Princess get heavier, their voices change accordingly.

Western Animation

 * In the second episode of South Park Cartman gains a lot of weight, and his voice gets deeper (and thicker).
 * It also happened to all of them in "Make Love, Not Warcraft".
 * Inverted in "Spontaneous Combustion", with Cartman's voice getting higher after losing a lot of weight.
 * Bender from Futurama may be a robot and thus find it hard to get fat but in one "What if..." episode where he becomes human and then lives as he normally does (which is to excess) he becomes extremely fat with a deeper, less excited voice.
 * Subverted in one episode of Scaredy Squirrel, where, after gorging on nutbars, Scaredy seems to have a deeper voice, but he just had a (still-wrapped) nutbar in his throat.
 * Mammoth Mutt in Krypto the Superdog whenever she inflates herself.

Real Life

 * Opera singers are often large, for one reason or another. At least one postulate is that they need the fat around their vocal cords to make those big sounds, and it's kinda hard to have a fat throat without having a fat everything.