Methods, devices, tools and assemblies for treating a patient to effect weight loss. One method embodiment involves passing a device including an expandable member in a collapsed configuration and a buoyancy member through an opening in the skin of a patient and into the abdominal cavity of the patient, and anchoring at least a portion of the expandable member, relative to at least one structure in the abdominal cavity. Devices including at least one expandable member and at least one buoyancy member are provided.