A gastric constriction device (160) comprises a sheet (131) extending over part of the wall of the stomach (24). Five bands (151) extend around the stomach (24) to fix the sheet (131) in position relative to the stomach (24). The lower two bands (151) extend from the first side (152) of the sheet (131) around the stomach (24) only partially towards the second side (153). These lower two bands (151) are not fixed to the second side (153). This arrangement results in an unconstricted portion of the stomach (161). In this manner, the device (160) restricts expansion of the majority of the stomach wall while facilitating expansion of this unconstricted portion (161). The unconstricted portion (161) is therefore free to expand or bulge outwardly upon ingestion. This expansion may trigger the feeling of satiation due to the presence of the vagal nerves in this portion (161) of the stomach (24).
