Rosemary Ellen Guiley said this quote

“ They may also ask that you bring certain types of food, alcohol, or tobacco on a regular basis. It must be noted that although djinn in their natural state might be composed of plasma, most of them can take a physical shape for short periods of time. This means that a djinni is able to take in nourishment by absorbing energy or consuming food. It's thought that many djinn enjoy the taste of a variety of our everyday foods, especially ice cream and fruits. Human foods only partially provide subsistence, however: djinn must get most of their nourishment by absorbing various types of energy from living things. ”