The objective of this dose-finding and feasibility study is to establish the optimal 13C-octanoate concentration to be used with slowly infused enteral nutrition to perform a prolonged gastric emptying test using the breath test. More specifically, the aim is to discover the 13C-octanoate concentration that induces a steady state hourly 13C-recovery. This would allow to implement the prolonged breath test protocol in a future clinical investigation in critically ill patients.

Inclusion Criteria:

• Signed Informed Consent
• At least 18 years old
• BMI between and including 18 and 29
• Understand and able to read Dutch
• In good health on the basis of medical history
• Refrains from herbal, vitamin and other dietary supplements on the day of the visits

Exclusion Criteria:

• Dyspeptic symptoms (assessed with PAGI-SYM questionnaire, Annex II)
• Using any medication that might affect gastric function or visceral sensitivity
• Known / suspected current use of illicit drugs
• Known psychiatric or neurological illness
• Any gastrointestinal surgery that could influence normal gastric function in the opinion of the investigator
• History of heart or vascular diseases like irregular heartbeats, angina or heart attack
• Nasopharyngeal surgery in the last 30 days
• Suspected basal skull fracture or severe maxillofacial trauma
• History of thermal or chemical injury to upper respiratory tract or esophagus
• Current esophageal or nasopharyngeal obstruction
• Known coagulopathy
• Known esophageal varices
• Have a known allergy or intolerance to cow milk, soy or any other ingredient of Isosource Standard.
• Known galactosaemia