The intervention in this study consists of 75-minute intraduodenal infusions of isosmotic solutions containing either saline (control), L-tryptophan, or calcium combined with L-tryptophan. Participants enrolled into the study will receive, in a randomised, double-blind fashion either (i) saline (control), (ii) L-tryptophan at a rate of 0.1 kcal/minute, (iii) combination of L-tryptophan (0.1 kcal/minute) + 500 mg calcium, or (iv) combination of L-tryptophan (0.1 kcal/minute) + 1000 mg calcium in four separate sessions, each of which will be separated by at least 4 (and up to 10) days. Each study session will be 4-6 hours. Studies will be carried out in the Clinical Research Facility of the Adelaide Medical School, the University of Adelaide, by staff and students trained in the required techniques.
Healthy, lean males (only men will be included in the study to avoid the confounding effects of the menstrual cycle on gastric emptying).
BMI: 19-25 kg/m2,
Weight-stable (i.e. <5% fluctuation) at study entry, which will be ascertained by a stable body weight in the preceding 3 months.
Significant GI symptoms, or history of GI disease or surgery
Current gallbladder or pancreatic disease
Cardiovascular or respiratory diseases
Any other illnesses as assessed by the investigator (including chronic illnesses not explicitly listed above)