Spinach was an Earth plant whose vegetation was often consumed as a source of nutrition.
Tom Paris personally enjoyed it in the form of both spinach juice and creamed spinach. (VOY: "Eye of the Needle", "Meld")
Benjamin Sisko also used spinach in his cooking, having prepared meals consisting of spinach linguine, as well as creamed spinach. (DS9: "For the Cause", "Equilibrium")