The Collaborative International Dictionary of English v.0.48:

Dietetic \Di`e*tet"ic\, Dietetical \Di`e*tet"ic*al\, a. [Gr. ?:
   cf. F. di['e]t['e]tique. See Diet.]
   Of or performance to diet, or to the rules for regulating the
   kind and quantity of food to be eaten.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dietetic
    adj 1: of or relating to the diet; "dietary restrictions" [syn:
           dietary, dietetic, dietetical]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "dietetic":
   cannibal, cannibalistic, carnivorous, commensal, dietary, dietic,
   dining, eating, feeding, flesh-eating, fruitarian, gastronomic,
   gluttonous, grain-eating, graminivorous, granivorous, grass-eating,
   herbivorous, insect-eating, insectivorous, lactovegetarian,
   man-eating, meat-eating, mensal, nourishing, nutritious,
   omnivorous, omophagous, pantophagous, phytivorous, phytophagous,
   plant-eating, postprandial, prandial, predacious, preprandial,
   vegetable-eating, vegetarian