system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do meal combinations become "boring" and unpleasant over time?

For example, if I eat rice and beans flavored with the same spices for several meals or days in a row, why do I get "sick" of that particular meal, yet enjoy it again if I go back to it after a hiatus?
gpt
Our bodies need a lot of different things in order to be healthy. Vitamins, minerals, etc. 

Different foods may have different toxins that the body has to deal with and expel, or it may have different vitamins that are absorbed differently and that enhance or inhibit absorption (ie: vitamin C and iron... calcium and iron).

Varying our diet means we're more likely to get what we need, not miss trace minerals, and not consume huge amounts of toxic substances that might be in a particular food (think of Taro root/cassava). 

We're probably genetically programmed to seek out and desire a variety of food sources to make sure our needs are met.