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 whether food grown on other planet, or trace elements, or certain specific plants.
Truth in Television
for various terrestrial animal species. Supertrope of Horror Hunger
. Compare Wizard Needs Food Badly
- The dinosaurs in Jurassic Park are deliberately given a genetic mutation that prevents them from producing lysine. Without lysine supplements provided by scientists on the island, they would all die off. (Only not really, because the dinosaurs figured out a way around that.)
- Gamma, one of Mickey Mouse's alien friends, survives on a diet of moth balls, or to be precise, naphthalene when he stays on earth.
- In Andre Norton's Catseye, 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 -- it was a lie.
- In Poul Anderson's "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.
- In Poul Anderson's "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.
- In T.J. Bass's dystopic Science Fiction novel The Godwhale, the genetically modified super-soldier was deliberately made unable to synthesize five (I think it's five) of the 17 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.
- The race of small furred aliens from the Fuzzy novels 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 the planet Zarathustra. Luckily, the humans brought a processed food to their world that contains the needed substance, and the fuzzies quickly become addicted to "esteefee".
- Martin from My Favorite Martian in one episode reveals that he needs trace amounts of gold in his system to remain healthy. Getting the necessary diet drives the episode. (One wonders why he didn't just buy and swallow some gold leaf used for gilding?)