Problem:
I'm wondering if mammals that can eat many different kinds of food (omnivores) vary their preference for food not only based on the availability, but also based on dietary needs.
I'm looking at this site Food nutritional content and see that "not all foods are created equal" - the vitamin/mineral and amino acid contents can vary dramatically.
Question: Is there some part of an omnivore brain/digestive system that "monitors" the micronutrient density of digested food and adjusts food preferences towards foods that make the diet more complete? Please suggest some answers.