The "Realm of the Hungry Ghost".
A hungry brain is in "hunting mode" until it's satiated. "Sugar" does not satiate the brain.
Increased consumption of plants results in an increase in receptors. These receptors can also be affected in gestation by the mother's diet. An example would be the "endocannabinoid" system.
Organisms produce nuerochemicals so that the host will continue to feed said organisms.
This is not an either/or scenario. It is common to have all of the above scenarios when not on a "species appropriate diet".
This applies to ALL species.