Diet evaluation gastric apparatus (18) is provided, which detects when a patient (10) swallows, and detects the type and amount of matter ingested. The apparatus includes electrodes (74, 100) adapted to be coupled to the fundus and antrum of the patient and to measure electrical and mechanical activity therein, and a control unit (90) to analyze such electrical and mechanical activity and optionally apply electrical energy to modify the activity of tissue of the patient.