What with all the exotic biologies hanging about, it's not exactly surprising that some Speculative Fiction characters need to eat things not in the ordinary run of things. This can vary widely, ranging from real-life trace elements or certain specific plants to food grown on another planet, Unobtanium or magical substances.
Failure to keep up with these diets can vary in effects. Less extreme cases will cause sickliness or the loss of special abilities. More extreme ones terminate in death by starvation.
This trope is often exploited by characters seeking to enslave or otherwise control a character or creature. If a being needs to consume a very specific type of thing to survive, then by controlling their supply of this substance one can force their obedience under threat of starvation. In some cases, this will be deliberately invoked during the creation of genetically engineered Bioweapon Beasts or Servant Races, which will be made dependent on the intake of rare, specialized or artificially-produced dietary supplements in order to create a tailor-made means of controlling them.
This is also especially common for aliens and other otherworldly beings. As these entities originate in environments very distinct from Earth's, whether simply alien biospheres or worlds with very different chemical or magical makeups from our own, their bodies will often be adapted to living with constant intakes of substances that on Earth are either rare or entirely absent. Thus, when traveling abroad, they will often have to regulate their diets to make sure that they don't find themselves lacking in something they need to live. This can lead to inversions of this trope if humans find themselves in alien worlds or other dimensions whose food simply doesn't nourish the human body as well as that grown on Earth.
A number of subtropes exist for this trope, as some specific types of diet are especially common in fiction; examples of those kinds go on their appropriate pages.
- Abstract Eater: Some characters need to feed on abstract concepts, such as ideas, emotions, colors or stranger things.
- Eat Dirt, Cheap: Some of these diets are, shall we say, more down to earth than others.
- Emotion Eater: Those that sup on sadness and dine on delight.
- Ingesting Knowledge: Knowledge itself — whether ideas in others' minds, words in books or the abstract concept of information itself — makes up the diet of some.
- Life Drinker: A character who stays alive indefinitely by consuming some vital force from their victims.
- Magic Eater: Some beings feed on arcane energies, whether they consume spells as they are cast or drain magic from creatures and objects.
- Metal Muncher: Many people need a bit of iron in their diet; some need quite a lot more.
- Phlebotinum Muncher: Whatever abstruse substance is important in the story, that's what these guys eat.
- Planet Eater: Some beings feed on nothing short of entire worlds, preferably inhabited ones.
- Soul Eating: Pneumavores, who consume the spiritual selves of their victims.
- Spacetime Eater: Some beings require no lesser food than the fabric of reality.
- Vampiric Draining: Some creatures need to feed directly from others, whether they drink blood or more abstract life forces.
This is Truth in Television for various terrestrial animal species. Related to Horror Hunger when their diet requirement is hard to get and/or is something questionable to eat. Compare Alien Catnip (drugs for fantastic creatures) and Wizard Needs Food Badly. See also Picky Eater and Picky People Eater. Sub-Trope of Food as Characterization. Compare Extreme Omnivore; while the Extreme Omnivore can eat almost anything, but doesn't typically require any one specific intake, someone with a Fantastic Diet Requirement needs to eat something unusual, either exclusively or as part of their diet. Contrast with I Do Not Drink Wine, in which a fantastic character cannot eat "normal" food. Compare and contrast Weird World, Weird Food, in which a fantastic culture is established through the use of strange food.
Examples
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Anime and Manga
- YuYu Hakusho: Some of the youkai races have to eat humans periodically in order to survive. Raizen dies of starvation after swearing off human as a result of falling in love with Yusuke's ancestor. It eventually turns out that the "cultivated humans" first shown in the Saint Beast arc are nutritionally equivalent without the issue of killing sentients for food.
Comic Books
- Mickey Mouse Comic Universe: Eega Beeva, one of Mickey's alien friends, survives on a diet of mothballs — or, to be precise, naphthalene — when he stays on earth.
- Star Wars (Marvel 1977): Hoojibs, aliens resembling mouthless rabbits, feed directly on energy, which they absorb through a flexible antenna on their heads, without needing to metabolize organic food for it. They normally feed on Power Crystals that occur naturally on their homeworld, but can also drain energy from machines.
Fan Works
- The Dragon King's Temple: Asyuntians and Go'auld have naquadah in their biochemistry, and as such require naquadah in their diets much as humans require iron or sodium.
- A Song of Silk and Saplings:
- Hornet, being part spider, is an obligate carnivore and liquivore. She cannot digest plant-based food at all, and can only digest animal-derived matter if it has been liquefied and partly pre-digested. Normally, she eats by simply hunting of her own accord in the way that spiders do — that is, webbing up her prey, injecting it with digestive enzymes, and then drinking up the remains — but in Bugaria, where carnivorous bugs are feared and hated, this causes her problems.
- Carnus the carrion beetle has a similar issue. He's a scavenger, which means that he can only digest decomposing meat. Unlike Hornet, who can at least hunt for herself, he's often reduced to robbing graves in order to eat the corpses.
- Under the Northern Lights:
- Nidhoggs eat nothing but frozen wood.
- Skolls feed on heat, preferentially that within other living creatures.
Film — Live-Action
- Jurassic Park (1993): The dinosaurs are deliberately given a genetic mutation that prevents them from producing lysine in order to keep them from spreading outside of InGen's control. Without lysine supplements provided by scientists on the island, they would all die off. At least, that's the plan — in practice, herbivorous dinosaurs adapted to feed on lysine-rich plants, while the predators get their lysine from their prey. Notably, in real life, no animals can actually produce lysine fast enough to meet metabolic demands, and all rely on their diet to supply themselves with it.
- The Smurfs 2: The Naughties need to drink a few drops of "smurf essence" (a liquid harvested from the sweat, tears, and hair of smurfs) or else they will get dizzy and weak and eventually die. This becomes a plot point when Gargamel refuses to give them any Smurf essence until Smurfette gives him the formula to turn them into real Smurfs.
- Star Wars: Mynocks feed directly on energy. In their natural environment, they subsist mainly on stellar energy emissions, but they will happily siphon off power from spaceship power circuits as well.
Literature
- Alice's Adventures in Wonderland: The Bread-and-Butterfly feeds itself with weak tea with cream in it, while the Snap-Dragonfly feeds on frumenty and mince pie.
- Animorphs: The Yeerks are sluglike parasites who wrap themselves around other creatures' brains to control them. Their main weakness is that they need to exit the host and absorb Kandrona rays in a pool every three days, with the host left caged by other Controllers or enjoying themselves in the case of voluntary Controllers. If the Yeerk isn't fed in time, it dies slowly and horribly, mentally torturing its host all the while.
- The Book of Dragons: In " We Don't Talk About the Dragon", the dragon is constantly wracked with burning, all-consuming hunger strong enough to be projected onto anyone in its vicinity. In the end, this is revealed to be because it needs to feed on gold, which even in small amounts can sate it entirely; the iron it was being fed on was enough to keep it alive, but wasn't enough to actually meet its dietary needs.
- Catseye (1961): Kyger claims that the Terran animals can not survive without the special food he provides, explaining to a patrolman why stealing one would be folly. Later, Troy sees them hunting and eating freely in the wild, revealing that this was a lie.
- A Certain Magical Index: The Artificial Humans known as Chemicaloids need their lollipops, because they neutralize toxins and were engineered that way.
- The Elric Saga: Elric requires a special diet of rare herbs and other things just to stay alive and envigoured. All this ends when he wins the hell-sword Stormbringer, which provides his energy from then on.
- The Giraffe and the Pelly and Me: The Giraffe belongs to a fictional subspecies known as the Geraneous Giraffe, which feeds exclusively upon the flowers of the tinkle-tinkle tree. It is noted that while the Monkey and Pelican can go without their preferred foods of walnuts and salmon, the Giraffe is doing poorly because the trio hasn't found any tinkle-tinkle trees since they arrived in England.
- The Godwhale: The genetically modified Super-Soldier was deliberately made unable to synthesize six of the seventeen amino acids necessary for him to stay alive. This means that he is dependent on the government/ruling class to provide him with a specially-compounded bread or he will die.
- Jurassic Park (1990):
- The dinosaurs were created to be dependent on artificial intake of lysine supplements to keep them from breeding outside of InGen's control.
- One of the characters from the rival companies speculates that InGen's greater plan is to genetically engineer toy breeds of their dinosaurs to sell as pets. They could get around the problems of the larger animal's diets by creating the toy breeds in such a way that they would only eat a special dinosaur food... which only InGen would sell.
- Known Space: The tree-of-life's microscopic symbiotes need soils rich in thallium oxide, a mineral common in the galactic core and rare everywhere else, to live. In turn, protectors need to consume tree-of-life root as their primary food source, and will starve without it.
- Little Fuzzy: The race of small furred aliens on the planet Zarathustra is slowly dying out when the humans first make contact with them, as their physiology demands nutrients with a specific chemical signature that's unavailable where they are living. This turns out to be proof they aren't native to Zarathustra. Luckily, the humans brought a processed food to their world that contains the needed substance, and the fuzzies quickly become addicted to "esteefee".
- The Railway Series: Henry the Green Engine is sickly and constantly under-performing in his duties due to his poor design and inability to burn coal properly, until he's finally given special high-grade "Welsh coal".
- Sharing Of Flesh: Every culture on a planet practices cannibalism as a coming-of-age rite for boys. The computer deduces that, because none of them have given it up despite the dangers it exposes them to, they must be biologically dependent on it.
- Starfog: One clue that the ship's crew are no longer human but have speciated is the salt they use. It contains traces of arsenic and other heavy metals they need and find food bland without.
- Star Trek Expanded Universe:
- In Doctor's Orders, Dr. McCoy reveals to Captain Kirk that not only is arsenic not a deadly poison for Klingons, but that it's a necessary part of the Klingon diet and Klingons have health problems if they don't consume enough arsenic.
- In the Star Trek: The Next Generation novel Debtor's Planet, Riker forgets that there's a whole list of Klingon foods that humans simply cannot consume because they are toxic to humans. He winds up needing to take a trip to sick bay after consuming the first dish on that list.
- Star Wars Legends:
- The Arcona species come from a planet rich in ammonia and need to supplement their diet with dactyl, a crystalline ammonia compound, while offworld. Conversely, common table salt is a potentially deadly Alien Catnip to them.
- Energy spiders feed on energy. By preference they prey on a type of non-sapient Energy Beings that share their homeworld, but they're equally happy draining the heat and life from organic lifeforms or absorbing blaster bolts.
- Strata: The Shandi have to eat a protein only found in other Shandi. If they don't they fly into a feeding rage. Fortunately they can synthesise the protein with a Dumb Waiter, good thing it couldn't possibly break down...
- The Witling: Inverted. The humans who are trapped on an alien planet know that they are being slowly poisoned by the high concentration of heavy metals in all of the food, which the aliens are unaffected by.
- Xanadu (Storyverse): A character who finds herself transformed into a slake moth ends up living on a diet of hallucinogen drugs — for her, it's that or human souls.
Live-Action TV
- The Addams Family: In "Uncle Fester's Illness", it's revealed that, without occasionally consuming mercury, Uncle Fester becomes lethargic and loses his electrical powers.
- Dark Angel: The X-5s have a genetic tryptophan deficiency. Max neglects to mention to her roommate, resulting in a couple of Mistaken for Junkie situations.
- My Favorite Martian: In one episode, Martin reveals that he needs trace amounts of gold in his system to remain healthy. Getting the necessary diet drives the episode.
- Star Trek:
- Star Trek: The Next Generation: In "Allegiance" the aliens holding Picard and two other aliens captive provide discs for their captives to eat, but the Chalna Esoqq cannot consume them as they are poisonous to him. This does nothing to improve Esoqq's mood, and he quickly comes to the point of being more violent than usual for members of his race.
- Star Trek: Deep Space Nine: The Jem'Hadar don't need to eat per se, but they need IVs of a drug called ketracel-white, or "white" for short, to survive. The drug not only provides a key enzyme that is missing from their systems, but also provides all the nutrition they need. This was done on purpose by the Founders who genetically engineered them to make them dependent and ensure their loyalty.
Mythology and Religion
- Norse Mythology: The gods need to eat mystical apples from the goddess Idun to retain their eternal youth.
Tabletop Games
- Changeling: The Lost: Characters with the merit "Arcadian Metabolism" are adapted to the Land of Faerie, so they begin to starve if they don't eat at least one goblin fruit per week on top of their usual diet. However, the fruit's healing properties are greatly magnified.
- Mechanical Dream: All races depend on a constant intake of eflow, a form of spiritual force, to survive. With the singular exception of the plant-based Frilin people, who generate it by meditating, they can also only obtain it by consuming orpee, a fruit-like plant found deep underground. Without daily intake of this food, a rapid and excruciating death is guaranteed. The politics, economics and culture of Kaïnas are almost soley driven by the collection and distribution of orpee, as it is an absolute requirement for life.
- Monte Cook's World of Darkness: Every demon has either a Kryptonite Factor or a daily craving for a specific odd substance, which can range from alcohol to uranium. It's a side effect of the power they use to create their earthly bodies.
- Warhammer 40,000: According to the first edition sourcebook Waaargh! Orks, the advanced intelligence of the ancient Orkoids was due to eating a very specific kind of fungus that stimulated brain growth. They were themselves unaware of this and, when they allowed the fungus to die out, they promptly regressed into their modern, primitive selves.
- Warhammer Fantasy Roleplay: The "Unnatural Appetite" Chaos mutation leaves the victim able to gain sustenance from only one thing. Options include grass, paint, and pets.
Toys
- BIONICLE: While not quite food, after being mutated by the waters of Aqua Magna, Krika has to constantly absorb heat from his environment; otherwise, his density power will go out of control and he will fade into nothingness. It's later rendered useless when Gorast gets angry and uses her Mask of Disruption, which makes his density power go out of control anyway and he promptly fades from existence.
Video Games
- Mass Effect:
- The asari homeworld Thessia has such high concentrations of element zero that traces are found in their food. The codex mentions that Thessian eateries make two separate menus, one with eezo, one without, and that asari living offworld have to take eezo in dietary supplements.
- All organic life is based on either dextro- or levo-oriented proteins, and can only digest and metabolize food with a matching chirality. Most sapients are levo-oriented and can live off of each other's foods easily enough, but turians and quarians come from dextro-based biospheres and have to take care not to eat foods meant for levo protein-oriented species.
"Don't eat the nuts in the red bowls. They're for turians and quarians only. You'll get cramps."
- Star Trek Online: The Victory Is Life expansion eventually reveals that the key ingredient in the Jem'Hadar life-giving drug ketracel-white is derived from a fungus originally from the Hur'q homeworld, and is a critical nutrient to the Hur'q. The Female Changeling rendered it extinct in nature in hopes of using the need for it to turn the Hur'q into Slave Mooks, but it Went Horribly Wrong and rendered the formerly civilized Hur'q an Ax-Crazy Horde of Alien Locusts instead.
- Xenoblade Chronicles 1: All life on the Bionis requires ether to survive in addition to food and water.
Webcomics
- Unsounded: Vliegeng, dragon like flying creatures, live off a strange giant grass called Frostgiants and while they'll sometimes eat a whale their necessary diet is Frostgiants which only live in northern Alderode limiting their range.
Western Animation
- Cybersix: All of Von Richter's creations require a substance called Sustenance to continue functioning, including the titular Cyber and her ally/brother Data-7. In fact, her initial reason for tracking Von Richter's group to Meridiana was less to stop his hostile takeover of the city and more to get Sustenance from his Mooks. Cybersix as Adrien can eat normal food and drink, but what, if anything, she derives from it beyond blending in is never explained.
- The Owl House:
- Inverted with Luz Noceda. As a human, she's unable to digest most of the food on the Boiling Isles and the food she can eat is implied to be rather pricey. This becomes a problem at the beginning of the second season after she destroyed the Earth portal at the end of the previous season to keep it out of Emperor Belos's hands, since the portal was previously used by Eda to collect either Earth food for Luz or human junk which she sold for money.
- Played straight with the Hexsquad after they are stranded on Earth for a few months during "Thanks to Them". Like Luz in the Boiling Isles, they are unable to eat most of the local dishes, forcing Camila to make lists in an attempt to narrow down the Hexsquad's palates.
- Steven Universe: Steven guesses that Lars and Lion might need to eat special crystal bugs to survive.
