Gastric apparatus, comprising: one or more sensors (70, 72, 74), adapted to generate respective sensor signals responsively to a gastrointestinal tract physiological parameter of a gastrointestinal tract of a subject; an implantable control unit, comprising a rechargeable battery and a first set of one or more transducers, the implantable control unit adapted to receive the sensor signals, and transmit data responsively thereto, using one or more of the transducers of the first set; and an external control unit, comprising a power source, a second set of one or more transducers, and a display screen, the external control unit adapted to: drive the power source to wirelessly transfer energy via one or more of the transducers of the second set, and receive the transmitted data, using one or more of the transducers of the second set, wherein the implantable control unit is adapted to receive the transmitted energy, using one or more of the transducers of the first set, and charge the battery using the energy, characterized in that: the external control unit is further adapted to be in connective interface with a remote service provider over a connection over which the external control unit is recharged, and send information to and receive information from the remote service provider, the external control unit is configured to send to the remote service provider eating-related information including a number of meals consumed per time period by the subject, and the external control unit is configured to (a) receive, from the remote service provider, subject-specific recommendations generated by the remote service provider based on an analysis of received eating-related information, and (b) display the subject-specific recommendations on the display screen. one or more sensors (70, 72, 74), adapted to generate respective sensor signals responsively to a gastrointestinal tract physiological parameter of a gastrointestinal tract of a subject; an implantable control unit, comprising a rechargeable battery and a first set of one or more transducers, the implantable control unit adapted to receive the sensor signals, and transmit data responsively thereto, using one or more of the transducers of the first set; and an external control unit, comprising a power source, a second set of one or more transducers, and a display screen, the external control unit adapted to: drive the power source to wirelessly transfer energy via one or more of the transducers of the second set, and receive the transmitted data, using one or more of the transducers of the second set, drive the power source to wirelessly transfer energy via one or more of the transducers of the second set, and receive the transmitted data, using one or more of the transducers of the second set, the external control unit is further adapted to be in connective interface with a remote service provider over a connection over which the external control unit is recharged, and send information to and receive information from the remote service provider, the external control unit is configured to send to the remote service provider eating-related information including a number of meals consumed per time period by the subject, and the external control unit is configured to (a) receive, from the remote service provider, subject-specific recommendations generated by the remote service provider based on an analysis of received eating-related information, and (b) display the subject-specific recommendations on the display screen.