system
Given the following post, respond as if you're commenting on Reddit:
human
[eli5] Why is it we generally tend to want certain foods at certain times during the day?

Are we just conditioned to have cereal/porridge/toast etc for breakfast, a sandwich for lunch and, for example, a hot meal for dinner?
gpt
Part of it has to do with you specifically; people grow up and get used to certain things, and so the body starts to expect those things along with your brain.

The rest has to do with what your body needs at that moment. If you’re craving milk really really bad, you may be low on calcium, or if steak seems like the best idea it might be iron. Your body uses a lot of nutrients and calories throughout the day, and cravings are usually how the body and brain tells you what you need.