Over the years, obesity has become a major public health concern. The increasing rates of obesity are associated with an enhanced demand for weight-loss with bariatric surgery as a treatment option. Bariatric surgery procedures alter the anatomical structure of the gastrointestinal tract, which contributes to the postoperative weight loss. However, it is not sure how obesity and the anatomical alterations of bariatric surgery affect the gastrointestinal physiology including gastrointestinal pH, gastric emptying, intestinal transit time and concentration of enzymes.

During the visit in the obesity clinic, eligible patients will be approached for participation by the sub-investigator. Interested patients will receive information regarding the study and receive the information sheet containing the informed consent form. After signing the informed consent form, volunteers will be invited to come to the clinical research center:

• Healthy volunteers: Gastrointestinal physiology will be analyzed during two visits using a telemetric capsule. During the first visit, the physiological conditions of interest will be analysed in fasted state using the telemetric capsule. During the second visit, the physiological conditions of interest will be analysed in fed state using the telemetric capsule.
• Obese volunteers: Gastrointestinal physiology will be analyzed during two visits using a telemetric capsule. During the first visit, the physiological conditions of interest will be analysed in fasted state using the telemetric capsule. During the second visit, the physiological conditions of interest will be analysed in fed state using the telemetric capsule.
• Obese volunteers: Gastrointestinal physiology will be analyzed during three visits using a telemetric capsule, scintigraphy and via the collection of gastrointestinal samples. During the first visit, the physiological conditions of interest will be analysed in fasted state using the telemetric capsule. During the second visit, gastrointestinal samples will be collected at the level of the stomach, the duodenum and jejunum via aspiration through multiple lumen catheters in fasted and fed state. During the third visit, gastric emptying will be observed via scintigraphy in fed state.
• Volunteers after Sleeve Gastrectomy: Gastrointestinal physiology will be analyzed during three visits using a telemetric capsule, scintigraphy and via the collection of gastrointestinal samples. During the first visit, the physiological conditions of interest will be analysed in fasted state using the telemetric capsule. During the second visit, gastrointestinal samples will be collected at the level of the sleeve, the duodenum and jejunum via aspiration through multiple lumen catheters in fasted and fed state. During the third visit, gastric emptying will be observed via scintigraphy in fed state.
• Volunteers after Roux-en-Y gastric Bypass: Gastrointestinal physiology will be analyzed during three visits using a telemetric capsule, scintigraphy and via the collection of gastrointestinal samples. During the first visit, the physiological conditions of interest will be analysed in fasted state using the telemetric capsule. During the second visit, gastrointestinal samples will be collected at the level of the pouch, the Roux limb and the common limb via aspiration through multiple lumen catheters in fasted and fed state. During the third visit, gastric emptying will be observed via scintigraphy in fed state.

Inclusion Criteria:

- 18 years or older

Exclusion Criteria:

• History of gastric ulcers
• Disorders of swallowing
• Suspected strictures, fistulas or physiological GI obstruction.
• GI surgery within past three months
• Severe dysphagia to food or pills
• Crohns disease or diverticulitis
• Use of implanted or portable electro-mechanical medical devices
• Known intolerance to the SmartPill device
• Known food allergies to any component of the meal
• History of multiple bariatric surgeries
• Pregnant or lactating women