If hunger is a reaction produced in the brain, based on visual perceptive clues, then can you explain the behaviour of
e. coli bacteria, which changes based on population density measured against food availibility?
Because, for all intents and purposes, even bacteria show behaviour consistant with hunger cues, despite having no nervous system whatsoever.
I think you're putting the cart before the horse - the cells signal a lack of nutrients; that signal is then processed by the brain, not the other way around. The cells say "we need to eat," the brain asks "what shall we eat," and the (mind, "I," self, whatever) signals the body to move towards obtaining and ingesting food.
By defining hunger as the "desire to eat," you allow for no other explanation of the phenomenon. Personally, I would say that the "desire to eat" is the conscious culmination of a long chain of events, most of which happen on biological levels far below cognition.
So, at the end of the day, it is the craving for food that makes you hungry.
No. It's the body's need for energy sources that cause hunger; it's the brain that turns that hunger to a desire for specific foods.