1570s, from Latin diaeteticus, from Greek diaitetikos "of or pertaining to diet," from diaita (see diet (1)). As a noun from 1759.
dietetic di·e·tet·ic (dī'ĭ-tět'ĭk)adj.
Of or relating to diet.
Of or being a food that, naturally or through processing, has a low caloric content.