Galanin is a protein found in the brain  In an experiment, rats that consistently chose to eat fatty foods when offered a choice between lean and fatty foods were found to have significantly higher concentrations of galanin in their brains than did rats that consistently chose lean over fatty foods
These facts strongly support the conclusion that galanin causes rats to crave fatty foods
The rats that preferred fatty foods had the higher concentrations of galanin in their brains before they were offered fatty foods.