Genius' Sweet Tooth

Thinking requires energy, right? Some characters, of course, do more thinking than others. These characters will need to have a quick pick-me up on hand, and most decide to eat some sweets. Perhaps the origin of this trope is the idea that showing a character eating sweets is a way to give the viewer clues as to his hyperactive nature, and it is harder to show the genius's mental hyperactivity on screen than another character's physical hyperactivity. Geniuses on TV also tend toward the socially immature and the eccentric, and showing them eating candy may be a clue to this. Even if a genius character isn't constantly binging on sweets, if he has a Trademark Favorite Food, it is likely to be sweet in flavor.

Actually Truth in Television: the brain uses glucose as its primary source of energy and not getting enough is bad. Therefore, if you need to make your brains work a lot, you may need at least some sweet food...

Contrast Is It Something You Eat?, where a character reveals his love of food, and his idiocy.

Anime and Manga

 * L and Mello from Death Note both ate sweets constantly. (In Mello's case, he was always ominously biting into some chocolate.)
 * Skuld in Ah! My Goddess, who can actually gain divine energy from ice cream.
 * Burn Up's Nanvel Candlestick: a world-renowned, award-winning inventor who demands Godiva chocolates and other sweets before she can work on anything. She never misses her three-o'clock snack, or her After-Dinner Dessert.
 * Professor Nova in Battle Angel Alita - pudding.
 * In Pokémon Special's Sinnoh arc, Professor Rowan is shown to have a fridgeful of sweets in his lab in Sandgem. In one early scene, he devours a cupful of sweets in less than 5 panels... and asks his lab assistant if he could also have the untouched serving.
 * Spanner from Katekyo Hitman Reborn loves lollipops and chain-eats them.
 * Yakumo Saitou from Psychic Detective Yakumo, though it differs between versions; in the Oda Suzuka manga, it's ice cream and muffins, and in the Miyako Ritsu manga, it's doughnuts.
 * Itachi Uchiha from Naruto plays with this trope. His favorite food is cabbage and onigiri (rice balls) with seaweed, but his hobby is visting sweet shops.
 * Once Bleach's Ikkaku bribed Urahara with a lolipop, said guy was seeing happily eating it with no problems.
 * Orihime Inoue is a Genius Ditz who loves doughnuts, according to the latest manga arc.
 * The Professor in Nichijou can always be expected to either be eating junk food of some kind, or trying to get someone to give her some.

Comic Books

 * Incredible Hercules' Amadeus Cho needs sugar to power his Hyper Awareness. He prefers chocolate, to the point that he fills the Olympus Corp building with chocolate vending machines and instructs employees to report any shortages immediately.
 * Chew takes this trope to new levels with characters who literally become geniuses when chowing down.

Film

 * Ghostbusters: Dr. Egon Spengler's sweet tooth was a little more obvious in the original cut. Still, it can be noticeably observed throughout the final product. (Venkman rewarding him with a candy bar, munching on a box of Cheez-Its, and of course, the Twinkie.)
 * In God of Gamblers, one of the titular genius gambler's distinctive trait is his love for chocolate (with an even distinctive way of eating) which he keeps even after he got amnesia. The chocolate eating habit is followed by his students in later movies, and in one particular movie, an impostor (though he eats the wrong kind of candy in different way of eating).

Literature

 * Dumbledore from Harry Potter loved all sorts of candies, and the passwords for his office were always names of sweets.
 * The exception being Every-Flavored Beans, seeing as he always seems to have the misfortune of eating one of the nasty ones.
 * The title character in "Swellhead" by Kim Newman.
 * The mentats in Dune use sapho juice to boost their already considerable mental abilities. It is desribed as cranberry-coloured and highly energetic, so it is probably sweet.
 * Hercule Poirot would sip down chocolate drink every morning, disgusting his partner Hastings.
 * Lord Auditor Georg Vorthys from Lois McMaster Bujold's Vorkosigan Saga is regarded as one of the Barrayaran Empire's top experts on Engineering Failure Analysis and has a Professor Emeritus post at Vorbarr Sultana University. He is very fond of desserts and makes regular trips to local bakeries to ensure that his supply of pastries does not run low. He also keeps a stash of cookies in his study.

Live-Action TV

 * In Doctor Who, the Doctor loves his jelly babies. The Second Doctor was the first to mention them, but "Would you like a jelly baby?" was the Fourth's Catch Phrase. The Eighth and Eleventh Doctors and John Simm's Master have both homaged it.
 * Jarod from The Prentender runs on PEZ.
 * Dr. K of 'Power Rangers RPM'' has actually sent the Rangers on shopping trips to the candy store. Her purchases are so large, the rangers must use a cart.
 * Reid from Criminal Minds always seems to be munching on something unhealthy, especially when he's thinking. It gets to be a running joke - the team will be investigating a crime scene without any obvious food sources, and then suddenly, sure enough Reid will pop up in the background, having located a vending machine or snagged a piece of leftover birthday cake.
 * In NCIS, both Abby and Gibbs seem to run on caffeine rather than sugar, though those Caf-Pow's are probably loaded with both.
 * Fringe: Walter Bishop loves his sweets.
 * Brenda Leigh Johnson in The Closer has a thing for processed sugar products, as well as (unsuccessfully) trying to cut back. In one episode, her team gives her snack cakes to help with the case.
 * The Leverage team tech-geek Hardison loves his orange soda and gummi frogs.

Video Games

 * Kokonoe of BlazBlue is a Mad Scientist Deadpan Snarker who is usually drawn holding a lollipop. Her lab, when the player finally sees it, has a few sweets laying around, too.
 * While not a "genius" in the traditional sense, the King's Quest guide says that Graham has a big sweet tooth.
 * In Apollo Justice: Ace Attorney, Ema Skye conducts her forensic investigations while snarfing down her Snackoo's.
 * Caillou from Recettear is a child wizard who keeps an eye out for promotional mud pies and used to go to church for the candy.

Western Animation
"Francine: I brought brownies Scientist#2: BROWNIES!!!. Scientist#1: ...He makes it hard to negotiate."
 * American Dad has one of the two CIA scientists who is more than willing to give away classified and potentially dangerous technology if offered brownies, at least Francine's.

Other Media

 * Julia Medvienekov, the Wrench Wench from an untitled R&S production, is a mechanical genius, who can frequently be seen eating chocolate.

Real Life
""“I'm going to eat crème brûlée and a huge number of chocolate truffles, and fight very hard to get you to see how wonderful Wagner is and how Brahms is not so wonderful.""
 * The human brain largely runs on sugar (among other things). Long periods of intense concentration burn through this sugar at a faster rate, making minor sugar cravings common for people involved in such work.
 * In his autobiography, Stephen Fry spoke of a long enduring love for sweets, especially as a child.
 * Andy Warhol was known for this. He visited pastry shops daily, sometimes buying an entire birthday cake for himself. He often refused more substantive meals, one time explaining to Tom Wolfe, "Oh, I only eat candy."
 * According to an interview conducted by the BBC in the 1990s, if Stephen Hawking were stranded on a deserted island with a very limited selection of luxuries and amusements, one of them would have been crème brûlée.
 * This is also referenced in the BBC drama Hawking (with Benedict Cumberbatch).