That's conditioned food and taste aversion, similar to Pavlov's dog. They say use a strong food stimulate before treatment like candy or something just before treatment so not to remind you of the bad taste later on from the last food you ate or even smelled. It is very psychological, sometimes, even color of room, ambience, food appearance, eat food that are familiar not exotic or new. Meats, certain proteins have more taste aversion, certain carbs less. Like Ed mentioned, counseling, psychologist is used to the see reason why there may be a mental reason causing anorexia, wasting or cachexia.