Measurement of gastric emptying rate of solid meal will be accomplished using 13C-octanoic acid breath test within 7 days after satiety test. After 12-hour fasting, the patient is required to ingest a pan-fried egg with 2 pieces of bread that contains 100 ul of 13C-octanoic acid dissolved in egg yolk. The exhaled gas will be collected at 15-minute intervals until 4 hours have passed. The 13CO2 content of the exhaled gas will be measured by a breath test device (FANci2, FAN GmbH.,Germany). 13CO2 is released after the 13C-octanoic acid enriched meal is emptied into the stomach and digested in duodenum.