The Mind reconfigures neural pathways.  Among those so configured are the pathways to/from the diencephalon where the Thalamus and Hypothalamus major control areas for the endocrine system are.  

Thus, what you think may become what you are.

Also, the Thalamus is the 'ante room' to the two cerebral hemispheres where higher cognitive functions are located.  As the body does its 'thing' messages are passed to the Thalamus through the Central Nervous System and the biochemical signals of the endocrine system.  Together these 'inform' the Thalamus which then transmits messages to the cerebral hemispheres.

Thus, what you are may become what you think.

Out of the googleplex of messages being transmitted eventually some of what you think will become what you are.  Out of the googleplex of messages being transmitted eventually some of what you are will become what you think.

On a simplistic level, the homeostasis system will generate signals to the Thalamus which send signals to the cerebral cortex which will result in the thought, "Let's go out for a pizza."

It works the other way as well.  That's how we can make the decision to hold our breath so we don't drown while swimming under water.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre