In fiction, being hungry and eating well often means being healthy. Adult characters are especially pleased with their children's healthy appetite. Conversely, if it's noted that a character hasn't eaten anything or that they have no appetite, there's a good chance that they're sick.
This has a basis in reality because there are many diseases that cause lack of appetite as a symptom (although there are also quite a few that have Inappropriate Hunger as a symptom as well), ranging from everything from the common cold to cancer. Certain mental illnesses, as well as simple stress, can suppress both the appetite and the immune system. It's also a good sign since, presumably, if the mind's free enough to worry about the stomach, it might not be consumed with other problems such as other types of discomfort.
Compare with Hyperactive Metabolism which is a video game dynamic that takes the ideas behind this and extends them to unrealistic levels. Compare to Forgets to Eat, where a lack of appetite indicates obsessive interest in a topic, rather than (or at least not necessarily) ill health, and Too Unhappy to Be Hungry where a lack of appetite indicates poor mood rather than health.
- Dragon Ball Super: a sign that something is seriously wrong with Goku after his use of Super Saiyan Blue and Kaio-Ken at the same time is the fact that he's not as hungry as he usually is. Keep in mind that for Goku and other Saiyans, a typical meal would feed a village for weeks on end, yet on this occasion, he's full after only one course. Chi-Chi is worried that it's a sign that Goku is dead, and King Kai later diagnoses him with a condition that interferes with his ability to use his ki.
- Rurouni Kenshin: After Yahiko recovers from a poisoned dart, Megumi, the medic who healed him, notes that his renewed appetite is a sign that he's recovering.
- Wolf Children: When toddler Yuki eats something she shouldn't have, Hana frantically calls a poison hotline. Fortunately the item was relatively harmless, and the person on the other end asks about Yuki's appetite. Since the girl is hungry, no harm is done.
- John Pinette, in his DVD I'm Starvin'! talks about how he had to shave his eyebrows to play the lead in a Broadway production of Hairspray, and how socially awkward it was (for context, it's important to remember Pinette weighed upwards of 350 pounds):
"When you have no eyebrows... people don't know what's wrong with you. They just see that you have no eyebrows, and maybe we should take the next elevator, honey. "He has no eyebrows! What's wrong with him? ...Well, if it's chemo, he's doing very well. He's keeping his appetite, God bless him!"
- Obelix gets this in conjunction with O.O.C. Is Serious Business:
Getafix: Did he eat anything?
Asterix: Two boars.
Getafix: Right, he didn't eat anything.
- In "The Chieftain's Shield", Vitalstatistix suffers an attack of biliarycolic that leads him to be sent to a spa in central Gaul. Unfortunately, he takes the gastronomic route to go there (with a montage of him eating while claiming the trope applies), with the result that a leaf landing on his gut triggers another attack, and he has to be carried to the spa. It only gets worse afterwards, since Asterix and Obelix aren't beholden to the patients' diet of boiled vegetables and thermal water and keep gorging themselves on roast boar in full view of the patients.
- Obelix gets this in conjunction with O.O.C. Is Serious Business:
- Towards the end of the last arc of Runaways, Klara is seen eating and drinking, showing that she is recovering from the various injuries and ailments that she suffered in the previous two issues. Of course, not long afterwards, she ends up vomiting it all up after developing motion sickness while riding around in the Leapfrog. Poor girl can't catch a break!
- A Day Without Leonardo: Leo's absence at the breakfast table is the first sign that he's not well.
- Dungeon Keeper Ami: In "Trouble Is Brewing":
"Worry about that later! Let' go back to the inn, we are missing breakfast!" Cathy suggested, tugging insistently on the smaller girl's sleeve.
"I can transport you back, but I'm still full from yesterday's celebration," Ami answered, lowering her gaze.
"Bullshit! You barely touched your meal. You didn't defeat that Reaper just so you could get done in by a lack of appetite! I'm making sure that you are eating right, and that's final!"
- In the Plants Vs Zombies 2 fanfic Glowing Reflections, one of the signs that Enchant-mint is ill is that he doesn't come to breakfast. He even Lampshaded this.
"Sorry, I'm not hungry."
- In Healin' Good 💖 Host Club, Honey being sick is revealed via him refusing breakfast.
- During the Kelp Forest arc of the Octonauts fanfic Junior Officers, Shellington being ill is signaled by his refusal to come eat breakfast.
- Ma Fille:
- In "Sick Day", Joe mentions being unable to eat a thing while he has a bad bout of the flu.
- Flipped around in "Showing Kindness", where Aran is shown to be feeling better via his appetite returning.
- In the Rugrats fanfiction Rugrats and the Gray Plague, one of the early signs Tommy has the titular ailment is him not wanting his sandwich.
- In the Encanto fanfic Sanded Down, the first sign that something's wrong is Bruno's absence at breakfast.
- In the sequel, Reflections in a Cloudy Sky, a similar situation occurs to signal Camilo being sick, however here it's his small portions rather than being absent from the table altogether.
- In The Season's My Reason, Rosemary's illness is first indicated via him being unable to eat breakfast due to nausea. Of course, coming from a food-based kingdom and being a Big Eater, he gets very scared and worries he may never be able to eat again.
- In the Supernatural fanfic A Winters Tale, despite the fact that Castiel was starving, he was having a hard time eating soup, indicating that he was getting sick.
- Inverted in Alien, when John Hurt's character is sitting down to dinner with a hearty appetite, the reason isn't that he's healthy, but (unbeknownst to the hapless victim) he's really eating for two... cue the Chest Burster.
- Early in Gone with the Wind, Mammy brings Scarlett a tray with food before the O'Haras leave for the Wilkes' barbecue; Mammy insists Scarlett shouldn't be seen eating much at the party to maintain a ladylike appearance. Scarlett initially refuses because, in her words, "Ashley said he likes to see a girl with a healthy appetite."
- Alice, Girl from the Future: In One Hundred Years Ahead, Fima Korolyov's grandmother is always afraid he is sick because he doesn't particularly want to eat. That's because by the time he arrives for his regular meals, he's usually had a lot of snacks with his friends.
- In one of the Amelia Bedelia books set in Amelia's childhood called "Amelia Bedelia Goes Wild", Amelia is sick with an unknown bug and is given lunch but she has no appetite and only eats a banana.
- Animal Farm: When discussing the issue of Mollie shirking her responsibilities, the narrator states, “[S]he complained of mysterious pains, although her appetite was excellent.”
- Charlotte's Web:
- When Wilbur feels too lonely and depressed to eat his slops, Mr. Zuckerman and Lurvey are concerned that he might be sick and give him sulphur and molasses as a tonic.
- When Mrs. Arable consults a doctor about her daughter Fern, concerned that her interest in spending time with farm animals rather than other children is unhealthy, one of the first things the doctor asks is whether she is eating well, to which Mrs. Arable replies that she has as large an appetite as ever.
- In the Dirty Bertie story "Pants!", Bertie doesn't want a potato crisp, so Darren says, "Are you ill?".
- In Emma, Miss Jane Fairfax is a girl with shattered health and she's also depressed because Love Hurts. Her doting aunt Miss Bates is worried constantly about the small amounts of food she eats.
- In Harry's Mad by Dick King-Smith, Harry's mother gets worried about the health of one of their parrots, Fweddy, because the latter has suddenly lost his appetite. Turns out, she is about to lay an egg.
- In Heidi, the invalid Clara never enjoyed her meals in her huge Frankfurt house much, rich and well made as they were. Being confined to a wheelchair and pampered like a doll didn't help her self-esteem or appetite. After going to the mountains with Heidi and getting some fresh air and simple, hearty food, her spirits are raised. The discovery that she had taken a second helping of toasted cheese is treated as a momentous event.
- Humanx Commonwealth: In Phylogenesis, Desvendapur claims to be too cold to eat after a strenuous escape in bad weather. He's coaxed into taking food, but dies overnight from exertion and exposure.
- In the sequel book to The Hundred and One Dalmatians, something weird has put all the non-dog animals to sleep and put all the dogs in this unusual state where one of the signs that something's up is that they no longer need or want to eat. Missus reassures Pongo that she's "not ill, just un-hungry."
- In Les Misérables, when the gravely ill Fantine thinks she's about to be reunited with her daughter Cosette, her condition improves, and for the first time in a long while she feels hungry. Even the doctor begins to have hope that she might survive. Unfortunately, she isn't reunited with Cosette, and succumbs to Death by Despair.
- In Little Women, Beth's appetite becomes "capricious" during her last year of life.
- In the kids book Mumps, the first sign that the boy has the titular disease is him saying, "I'm not hungry".
- In the Roys Bedoys book "Get Well Soon, Roys Bedoys", the title character is sick with what appears to be either a serious cold or a very mild flu. He is offered chicken soup, but doesn't want it as his appetite is gone.
- In The Secret Garden, a sign that Mary is getting fitter (though she was never sick) is feeling hungry.
- In the Sesame Street book Nobody Cares About Me, two of the reasons why Big Bird envies the sick Ernie are that Bert makes soup just for him and Cookie Monster brings him cookies. But when Big Bird catches Ernie's cold, and Bert and Cookie Monster visit him with soup and cookies, he feels too sick to eat.
- In Shakespeare's Scribe, Widge, a former doctor's apprentice, examines a girl name Tetty who fears she's caught the plague. After a brief inspection for plague symptoms, finding none, Widge asks if she's lost her appetite. She confirms she's hungry, reassuring her that she's not plague-infected.
- In Six of Crows, Nina Zenik (whose introduction in the book is marked by her wolfing down a slice of cake, and brings toffees when told to pack essentials) is a noted Big Eater. After she takes the jurda parem, she loses her appetite from withdrawal. In Crooked Kingdom, her regaining her appetite is a sign that she's recovering.
- In the fifth book of the Sword of Truth series, Zedd claims he is fine, but then immediately goes on to refuse food. Since he is the Big Eater of the series, the rest of them get worried.
- Temeraire: Among other symptoms, the sick dragons in Empire of Ivory lose their appetites, which actually exacerbates their illness due to malnutrition. Their human companions try to fight this by over-spicing their food so they can still enjoy it despite their deadened sense of taste.
- The Wheel of Time: When Mat is cursed by an Artifact of Death, his appetite disappears until he is Nothing but Skin and Bones. After the curse is removed, he has to eat several times the normal amount, both to restore his body and to fuel the magic that is healing him.
- Gilligan's Island: In "Gilligan Gets Bugged", the castaways think Gilligan has been bitten by a deadly bug, the mantiscani. One of the symptoms of a mantiscani bite is total loss of appetite. The girls think Gilligan is exhibiting symptoms when he doesn't eat a coconut cream pie they bring him (especially given that it's his favorite), but actually he's just been snacking on bananas and has no room left.
- M*A*S*H: After Klinger has a Fever Dream Episode and talks to a dead soldier, at the end of the episode he wakes up in post-op and reports that he's hungry. Margaret: "That's a good sign."
- Sesame Street:
- In one episode, Barkley has the dog equivalent of a cold and isn't eating. Maria and Big Bird think this is serious.
- Played for Drama when a little girl's fish looks sick and doesn't eat his food, then dies.
- In a live-action skit with the song "You Have to Be Patient to Be a Patient", a little girl is seen refusing her porridge, so her father takes her temperature and shakes his head.
- In Sesame Street Home Video Visits the Hospital, when the hospital is working to diagnose Big Bird's lung infection, Maria is asked about his appetite and replies that lately it's been so-so. Toward the end of the special, he's shown ordering every item on the hospital menu for lunch: an obvious sign that he's getting better.
- In the eighth episode of Squid Game, Sae-byok barely touches her steak dinner, claiming that it doesn't taste good, despite it being leagues above anything else they've had during the games (the previous meal was a raw potato). This turns out to be because her stomach was pierced by a shard of glass after the previous game. Her health quickly dwindles afterwards, leaving her defenseless when Sang-woo comes to kill her.
- Star Trek: The Next Generation: In "Thine Own Self", aliens wonder if Data is unwell because he has no appetite. Actually, it's because he's an android, but he couldn't inform them because he didn't know so at the same time: a malfunction had caused him to lose his memory.
- In Supernatural, Dean Winchester is a notorious Big Eater. This is why it's such a concern in "My Bloody Valentine" when Dean is the only one who doesn't have a voracious appetite. The horseman Famine is causing people to gorge themselves to death and his power is so strong it even affects the angel Castiel who normally doesn't need to eat, but suddenly finds himself uncontrollably downing red meat, a favorite food of his vessel, Jimmy Novak. In the end, Famine claims that the reason Dean isn't affected like everyone else is that Dean is already dead inside, so there's no hidden desire or appetite to stoke.
- Inverted in the episode of It's Always Sunny in Philadelphia "Mac and Dennis: Manhunters", where Dee and Charlie get a craving to eat meat after thinking they've eaten a person. Their extreme hunger is a symptom. Eventually, it turns out that they're infected with a tapeworm.
- Seinfeld: Elaine hears that an ex-boyfriend of hers is deathly ill and goes to visit him in the hospital. She had previously broken up with him for being too fat, but his illness has made him lose his appetite, so he is now skinny. Finding him more attractive this way, she gets back together with him. By the end of the episode, he has made a miraculous recovery, and is seen stuffing his face with the implication that he's going to quickly gain all of his weight back. Elaine sits there watching him eat, looking incredibly regretful of her decision.
- In the children's song On Being Sick, one lyric is "You may not have an appetite". Despite this, they mention the child enjoying treats.
- In one children's song, Fred Penner's Ebeneezer Sneezer, loss of appetite is one of the title character's symptoms after he gets sick from playing outside in the cold without warm clothes.
- In the 1929 song I Got a Code in My Doze (most famously sung by Betty Boop in "Betty Boop's Ker-Choo" and by Barbra Streisand in Funny Lady), one lyric is "I can't sleep, I can't eat./Get a pail and soak my feet."
- Zigzagged in Neopets: While the pets can be hungry and sick, and they're often healthy and not hungry, some diseases have "refuses to eat" as a symptom.
- In Star Ocean: Till the End of Time, after Cliff and Mirage rescued Maria after she escaped from a spaceship wreckage, after which she had lost both her parents, after she wakes up, they worry that she might still be injured. When she replies that she's hungry, both laugh in relief, and Cliff tells Mirage to get her some food.
- In the Pokémon Mystery Dungeon series, Hunger is its own stat that will deteriorate your character if not fulfilled for long enough.
- Inverted in Red Dead Redemption II. When Arthur gets really sick with TB, his health and stamina cores actually empty faster than when he's healthy. This is most likely to imply he gets tired quicker, not that he's hungry, but the cores are replenished when you eat.
- In Better Days, increased appetite is used as a sign that Persia is recovering after Fisk rescues her from prostitution and heroin.
- In Freefall, Florence gets wounded and loses a lot of blood. The doctor says that she's going to have no appetite for a while, while her body concentrates on regenerating said blood, and they'll know she's fine when she suddenly becomes ravenous. Cue Oh, Crap! from Sam as he realizes that means that in a few days he's going to have an extremely hungry large predator that can open doors loose in his ship, and it'll probably happen when he's asleep.
- Charlie and Lola: In "I'm Really Ever So Not Well", Lola has a cold and says, "I don't feel like eating or drinking anything!".
- In Hey Arnold!, one of the symptoms that worries Helga that she might have monkeynucleosis is a lack of appetite. However, this is a subversion, as it turns out that the entire thing was all in her head. Since lack of appetite can also be a symptom of stress, it's likely that's where the lack of appetite came from.
- In the Little Princess episode "I Don't Want a Cold", the narrator thinks it's a good sign when the Princess says she's hungry.
- In the original Madeline special, when Madeline is first showing signs of being sick, she refuses to take her usual bite from the snowman's carrot nose at the skating pond, and at dinner, she slips her bread to her two mouse friends. Particularly justified, since she has appendicitis, which is characterized by an upset stomach.
- Owen from Total Drama is a Big Eater. However, in Total Drama Action, there were two instances when he had trouble eating.
- After eating the prop food that he mistook for actual food in the first episode of Action, the next episode he suffers from indigestion and he lost his appetite. Everybody was surprised when he chose to eat some prunes over pancakes.
- After Chef threw a massive book at Owen that broke his jaw in the disasters challenge, he was forced to only drink blended food through a straw for a while, which caused him another digestive problem. After he heals, he's back to enjoying normal food.
- The Simpsons: In one episode, the family decides to do their grocery shopping from Cletus vegetable stand (the Kwik-E-Mart was in the middle of a robbery), which results in everyone except Lisa getting sick with symptoms resembling the flu and unable to keep any food down, even Homer. As it turns out, the rest of the Simpsons are so used to processed food that organic vegetables containing actual vitamins and minerals was a massive shock to their system. Lisa, being a vegetarian, was immune, and spends a few days taking care of the others while they recover, which is shown by them happily devouring a bucket of fried chicken.
- Elizabeth I is reported to have completely lost her appetite and refused all food and drink in her final days.