Humans need food to survive. Many of the characters of the Star Wars universe, human or otherwise, are depicted eating for just that reason. Despite being mostly human, however, there is no clear way for Darth Vader to get sustenance to the part of his face that accepts food. This is, of course, a mystery easily solved.
I don't read or speak French, but the visuals are mostly self-explanatory: Due to the presence of moisture and milk-producing mammals in Star Wars, we can clearly conclude that on any given day, an iconic space villain walks around with grated cheese stuck to his face.