Effects of calcium and amino acids on gut hormone secretions and bone turnover in healthy males

INTERVENTION: The intervention in this study consists of a 150 min intraduodenal infusion of a calcium or control solution, combined with L‐tryptophan (0.1 kcal/min) from t=75‐150 min. Participants enrolled into the study will receive, in randomized, double‐blind fashion (i) 500 mg CaCl2, combined with L‐tryptophan (0.1 kcal/min) from t=75‐150 min (ii) 1000 mg CaCl2, combined with L‐tryptophan (0.1 kcal/min) from t=75‐150 min (iii) Saline (control), combined with L‐tryptophan (0.1 kcal/min) from t=75‐150 min each occurring at separate visits. Each visit will last 4.5‐6 hrs in duration and will be separated by 3‐7 days. Visits will be carried out in the Clinical Research Facility of the Discipline of Medicine, the University of Adelaide by staff members trained in the required techniques, and will be conducted on an individual basis. Participants will be asked to consume a standardised dinner meal (Beef lasagne; total energy content: 602kcal; McCain Food, Wendouree, Victoria, Australia) the night before each visit by no later than 6 pm, After fasting for 14 hrs overnight and refraining from exercise and alcohol for 24 hrs, participants will arrive at the laboratory at 8 am. Upon arrival, participants will be intubated with a 17‐channel manometric catheter that will be inserted through an anaesthetised nostril and allowed to pass through the stomach and into the duodenum by peristalsis. The manometric catheter consists of 16 side holes spaced at 1.5 cm intervals, measuring pressures in the antrum, pylorus, and duodenum (APD pressures). An additional channel (with the side hole positioned approx 14 cm distal to the pylorus when the catheter is in position) is used for intraduodenal infusions. The correct positioning of the catheter will be maintained by c CONDITION: Diet and Nutrition ‐ Obesity Healthy human gastrointestinal physiology;Healthy human bone turnover physiology; ; Healthy human gastrointestinal physiology ; Healthy human bone turnover physiology Metabolic and Endocrine ‐ Normal metabolism and endocrine development and function Musculoskeletal ‐ Normal musculoskeletal and cartilage development and function Oral and Gastrointestinal ‐ Normal oral and gastrointestinal development and function SECONDARY OUTCOME: Antropyloroduodenal (APD) pressures. ; [This will be measured continually for 150 min (t = 0‐150 min) using the manometric catheter, measuring pressures in the antrum, pylorus, and duodenum. ] Appetite ratings (hunger, fullness, desire to eat, and prospective consumption), and GI symptoms (nausea and bloating). ; This outcome is of an exploratory nature so that specific parameters to be measured may be decided upon based on the effect of the intervention on this and other outcomes, therefore, this is a composite outcome. ; [This will be measured using a 100mm Visual Analogue Scale (VAS). This VAS has been extensively employed in published studies conducted by the investigators. ; VAS will be collected before infusion (t= ‐15) and during study at regular time points for 3 hours (t= 0,15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 180)] Energy intake at a buffet lunch. ; [ At t=150, participants will be presented with a standardised cold, buffet‐style meal, which is used to assess energy intake. The meal comprises 4 slices ( 120 g) of whole‐meal bread, 4 slices ( 120 g) of white bread, 100 g sliced ham, 100 g sliced chicken, 85 g sliced cheddar cheese, 100 g lettuce, 100 g sliced tomato, 100 g sliced cucumber, 22 g mayonnaise, 20 g margarine, 1 apple ( 170 g), 1 banana ( 190 g), 175 g strawberry yogurt, 100 g chocolate custard, 120 g fruit salad, 375 mL iced coffee, 300 mL orange juice, and 600 mL water. The meal has a total energy content of 2300 kcal ( 27% fat, 52% carbohydrate, and PRIMARY OUTCOME: Markers of bone remodelling and calcium homeostasis (CTX, PTH)[These will be assessed from venous blood samples taken before infusion ( t = ‐15, ‐5) and during study at regular time points for 3 hours (t= 5, 15, 30, 45, 60, 75, 80, 90, 105, 120, 135, 150, 180 min)] Plasma concentrations of GI hormones (gastrin, CCK, GIP, GLP‐1, and potentially other, including yet to be identified, gut hormones), and glucose.; This outcome is of an exploratory nature so that specific hormones to be measured may be decided upon based on the effect of the intervention on this and other outcomes, therefore, this is a composite outcome.[These will be assessed from venous blood samples taken before infusion ( t = ‐15, ‐5) and during study at regular time points for 3 hours (t= 5, 15, 30, 45, 60, 75, 80, 90, 105, 120, 135, 150, 180 min)] 21% protein)and weight of 2924 g. Participants will be allowed 30 min to freely consume food until they are comfortably full. Each food item will be weighed before and after being offered to the participants and energy intake and macronutrient composition calculated using commercially available software (Foodworks 8.0, Xyris Software, Highgate Hill, QLD, Australia). ] INCLUSION CRITERIA: Healthy Lean weight (BMI 19‐25 kg/m2)