To elucidate the mechanism of re-gaining body weight and possible ghrelin expressing cell hyperplasia, the investigators designed the prospective study to investigate the stomach tissue as well as plasma ghrelin in the patients who are going to have Billoth surgery. The items to be investigated include plasma for hormones (ghrelin, leptin, insulin, CCK, PYY), stomach tissue for ghrelin, diet evaluation and body weight (body mass index) changes for 7 months after gastrectomy.