It’s not specific or precise. You cast a wide net to meet needs based on what your brain thinks you need and where you can get it. The part of your brain that says I’m thirsty might not work well but some other part convinces you to drink anyway, otherwise you wouldn’t be alive. Your nutrient needs can get met by a variety of sources. Maybe your system adapts well to just the basics. If it gets x proteins and y carbs, it’s happy. The part of a brain that develops cravings in other people hasn’t needed to develop in you. Or maybe stomachs needs a certain nutrient that yours produces naturally while others have to seek it out.