A dieting device which prevents or inhibits oral ingestion of food is disclosed. The device comprises at least one pair of frames which are secured to the maxillary and mandibular dentitions respectively, or part thereof, of a wearer. One of the frames has mounted to one side thereof one or more permanent split pole magnets which magnetically attract either a corresponding set of magnets or a ferromagnetic mass mounted to one side of the corresponding frame secured to the alternate dentition to ensure that the jaws are constrained to assume a permanently or semi-permanently occluded condition. The magnetic attraction between upper and lower dentitions to which the frames have been applied is not so great so as to be impossible to overcome by the wearer and thus the jaws can be opened in an emergency, but in use the frames will make mastication, and thus oral ingestion of food very difficult.