Alice is a giantess living amongst humans, and her size requires a lot of food.
Alice is pregnant.
Alice used to be anorexic and is now eating tons of calories to try to resume a normal body shape.
Alice has Prader-Willi Syndrome, which is a condition where the hypothalamus, which controls appetite, malfunctions, making the one who has it feel like he or she is starving no matter how much or often they eat.
Subverted: Alice is shown eating pounds and pounds of food. When asked why she ate so much, it was because she was starving for many days.
Double Subverted: ... Until Alice is shown eating that amount the next day.
A bad guy tries to use ironic torture, feeding Alice a literal mountain of food. The scene changes and returns five minutes later to show Alice, happily wiping crumbs off, next to the space where the mountain used to be.
Alice eats at a restaurant and the camera cuts to the inside of the kitchen showing the chefs struggling to keep up with Alice's excessive orders or running out of ingredients and rushing to get more.
Zig Zagged: Alice eats heavily one meal, then eats very little the next. Then she eats all the food in a restaurant. Then she doesn't eat at all.
Averted: Alice eats the amount of an average woman her age.
Lampshaded: "Wow Alice, haven't you noticed that you're eating a bit too much?"
Invoked: "Hmm, if we disguise the vegetables as pizza and junk food, Alice will actually eat something healthy!"
Exploited: Alice's enemy poisons the supply of Alice's Trademark Favorite Food, confident in the knowledge that she will be the one to eat it.
Alice is given the choice to either eat a plate or food, or a whole table of food. She choses the plate.
"Of course I won't eat that much food! What do I look like?!"
Discussed: "Have you noticed that Alice eats more than a normal person would per day?"
Implied: Alice was left in a room with a huge table of food, when they came back, it was gone.
Alice's eating causes a localized food shortage, and therefore famine. Her eating also has serious health repercussions later down the road.
Alice becomes obese due to her heavy eating, and has all the health problems that come with it.
One of Alice's friend's meals is poisoned. Bob doesn't stop at his own meal, and eats her friend's poisoned meal, inadvertently saving her.
Alice's overeating turns out to be a (nearly) Fatal Flaw.
After consuming a inhumanly large amount of food, Alice vomits or her stomach bursts open.
Alice is a world-famous eating contest champion, and practices every day by consuming large amounts of food to expand her stomach, and drinking loads of water and exercising a lot to burn all the extra calories away.
Alice does her best to resist eating too much.
Alternatively, Alice finds a food known for being extremely filling, and eats mostly this.
Alice has an incredibly fast metabolism, and can eat quite a bit without gaining weight.
Played For Drama: Alice is bulimic or has Binge Eating disorder.