A medical apparatus comprises a control system allowing storage of a number of shaping profiles. Each shaping profile is stored as a plurality of pairs, including a shaping profile reference value and a time interval value. The reference value is represented as fraction, for instance a percentage, of the total weight loss the apparatus should achieve at the end of a treatment time. Each time interval value is represented either as fraction of the total treatment time or as a prefixed actual time interval. The control system calculates the actual weight loss rate versus time profile based on the desired total weight loss, on the desired total treatment time as well as on selected desired shaping profile.