The invention comprises a gastric device having an outer region and a gas producing material. The gastric device hydrates within a patient's stomach and the gas producing material expands the device to a greater volume. Accordingly, the volume of the hydrated, expanded gastric devices occupy space in the stomach cavity and reduce the amount of food the patient will ingest before reaching the feeling of fullness. Preferably, the gastric device is made from food grade materials. The gastric device is configured to expand to a desired volume and then degrade after a residence time, allowing the device to be passed by the patient's normal digestive process.