If I fed you the same diet of (let's say) rice, lentils, carrots, broccoli, and cheese for every meal, every day, you'd soon get sick of it. You might start dreading mealtimes, knowing that the food will be the same. It's not that you specifically crave something else; you just want something different.
I get the impression that this "food boredom" phenomenon occurs in every culture, which would indicate a genetic rather than cultural basis. But what evolutionary advantage could there be to rejecting a perfectly healthy meal, just because it's the same one you had yesterday?
Consider a typical omnivore, or any other creature that eats a highly variable diet. It forages (and maybe hunts), but isn't guaranteed to find any one type of food. Food may appear suddenly in large quantities (a full apple tree produces a windfall, a deer is hit by a car), and at those times the animal must gorge on the bounty. Sometimes the time of plenty lasts much, much longer, and the animal forgoes normal foraging behavior.
Given unlimited fat and sugar, humans will eat to morbid obesity. Our ancestors could not be guaranteed a steady diet of these precious substances, so there was no danger in unchecked cravings.
Other animals at the middle trophic levels will of course exhibit the same behavior. If the food source does not contain fats, carbohydrates, balanced protein, and a full complement of vitamins and minerals, but instead a limited subset of these, then continued feeding will result in a deficiency or imbalance.
This, I believe, is where food boredom comes in. If an animal continues to eat the same food day after day, it is probably losing out on other, more challenging food opportunities that would lead to a balanced diet. By becoming increasingly dissatisfied with the easy food, the cravings are specifically suppressed and redirected elsewhere. Other food sources become much more appealing, even ones that are much less attainable.
So if food boredom acts to reduce "lopsided" gorging, why does it kick in for balanced diets, too? My explanation is that complete, fully balanced diets do not occur as "windfalls" in the natural world, and thus there is no reason for the body to make an exception.
What are your thoughts? Is the phenomenon truly cross-cultural? Is there an alternative explanation?