Effects of Combined Administration of Calcium and L-tryptophan on Gut Functions and Blood Glucose in Healthy Humans

NCT07013656 | Not Yet Recruiting

• 1 other identifier: 13243
• Study Type: interventional
• Target: 16
• Locations: 1 country
• Sites: 1

Brief Summary

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.

Conditions

Healthy

Keywords

Intraduodenal; Calcium; L-tryptophan; Gastric emptying; Glucoregulatory hormones; Plasma glucose; Human

Outcome Measures

Primary Outcomes (1)

• Plasma glucose concentrations

  Plasma glucose concentrations (mmol/L) will be assessed using the glucose oxidase method.

  Blood samples will be collected over 4.5 hours: at baseline (time = -30 minutes), then at regular intervals before and after drink administration (times = -25, -15, 0, 10, 20, 30, 45, 60, 75, 90, 120, 180, and 240 minutes).

Secondary Outcomes (3)

• Gastric emptying

  Breath samples will be collected in sealed tubes over 4.5 hours: at baseline (time = -30 minutes), prior to treatment administration, every 5 minutes after the drink (times = 0 to 60 minutes), and then every 10 minutes until 240 minutes post-drink.

• Plasma concentrations of glucoregulatory hormones e.g. glucagon-like peptide (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), C-peptide, glucagon, insulin and cholecystokinin (CCK)

  Blood samples will be collected over 4.5 hours: at baseline (time = -30 minute), then at regular intervals before and after the drink (times = -25, -15, 0, 10, 20, 30, 45, 60, 75, 90, 120, 180, and 240 minutes).

• GI symptoms (nausea and bloating) will be assessed as a composite secondary outcome.

  VAS questionnaires will be collected over 4.5 hours: at baseline (time = -30 minutes), at regular intervals before and after the drink (times = -15, 0, 10, 20, 30, 45, 60, 75, and 90 minutes), then every 10 minutes until 240 minutes post-drink.

Study Arms (4)

L-tryptophan

ACTIVE COMPARATOR

In this arm, participants will receive a 75-minute intraduodenal infusion of an isotonic solution containing 1.83 g L-tryptophan, dissolved in 225 mL distilled water. Additionally, 2.2 g of sodium chloride (NaCl) will be added to ensure the solution is isosmotic (\~373 mOsm).

Other: L-tryptophan

L-tryptophan + Ca-500

ACTIVE COMPARATOR

In this arm, participants will receive a 75-minute intraduodenal infusion of an isotonic solution containing 1.83 g L-tryptophan and 1.84 g of calcium chloride dihydrate (CaCl₂·2H₂O), dissolved in 225 mL of distilled water. Additionally, 1.1 g of NaCl will be added to ensure the solution is isosmotic (\~373 mOsm).

Other: Combination of L-tryptophan + Ca-500

L-tryptophan + Ca-1000

ACTIVE COMPARATOR

In this arm, participants will receive a 75-minute intraduodenal infusion of an isotonic solution containing 1.83 g L-tryptophan and 3.68 g of calcium chloride dihydrate (CaCl₂·2H₂O), dissolved in 225 mL of distilled water. This solution has an osmolality of \~373 mOsm.

Other: Combination of L-tryptophan + Ca-1000

Control

PLACEBO COMPARATOR

In this arm, participants will receive a 75-minute intraduodenal infusion of saline (an isotonic solution containing 2.5 g of NaCl, dissolved in 225 mL of distilled water). This solution has an osmolality of \~373 mOsm.

Other: Control

Interventions

L-tryptophan OTHER

L-tryptophan, an aromatic amino acid and one of the building blocks of protein, is a part of our daily diet. The load of L-tryptophan (0.1 kcal/minute) is based on our previous study, in which L-tryptophan represented a submaximal load.

L-tryptophan

Combination of L-tryptophan + Ca-500 OTHER

Calcium, an essential mineral and a key component of dairy products, is a regular part of our daily diet. In this condition, both L-tryptophan and calcium will be administered as 'active'. Recent studies have shown that calcium in a dose of 500 mg enhances the effects of L-tryptophan to stimulate gut functions and reduce energy intake. This dose of calcium will be considered 'lower dose'.

L-tryptophan + Ca-500

Combination of L-tryptophan + Ca-1000 OTHER

In this condition, both L-tryptophan and calcium will be administered. In our study calcium in a dose of 1000 mg enhances the effects of L-tryptophan to stimulate gut functions and reduce energy intake. This dose of calcium will be considered 'higher dose'.

L-tryptophan + Ca-1000

Control OTHER

An isotonic solution containing 2.5 g of NaCl, dissolved in 225 mL of distilled water.

Control

Eligibility Criteria

• Age: 18 Years - 70 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• 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.

You may not qualify if:

• 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)
• Use of prescribed or non-prescribed medications (including vitamins and herbal supplements) which may affect energy metabolism, GI function, body weight or appetite (e.g. domperidone, cisapride, anticholinergic drugs (e.g. atropine), metoclopramide, erythromycin, hyoscine, orlistat, green tea extracts, Astragalus, St Johns Wort etc.)
• Lactose intolerance/other food allergy(ies)
• Individuals with low ferritin levels (\<30 ng/mL), or who have donated blood in the 12 weeks prior to taking part in the study
• High performance athletes
• Current intake of \> 2 standard drinks on \> 5 days per week (\>140g/week)
• Current smokers of tobacco (cigarettes, cigars, pipes, sheesha, chewing, vaping etc.)
• Current use of recreational drugs, e.g. marijuana
• Current intake of any illicit substance
• Vegetarians
• Inability to tolerate nasoduodenal tube
• Inability to comprehend study protocol

Sponsors & Collaborators

• University of Adelaide: lead

Study Sites (1)

Clinical Research Facility, Adelaide Health and Medical Sciences Building

Adelaide, South Australia, 5005, Australia

Location

MeSH Terms

Interventions

Tryptophan

Intervention Hierarchy (Ancestors)

Amino Acids, Aromatic; Amino Acids, Cyclic; Amino Acids; Amino Acids, Peptides, and Proteins; Amino Acids, Essential

Study Officials

• Prof Christine Feinle-Bisset

  Adelaide Medical School University of Adelaide Level 5 Adelaide Health and Medical Sciences Building, Cnr George St and North Tce, Adelaide, SA 5005

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Prof Christine Feinle-Bisset

CONTACT

+61 8 8313 6053; christine.feinle@adelaide.edu.au

Penelope Fitzgerald, MsC

CONTACT

+61883136278; penelope.fitzgerald@adelaide.edu.au

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: TRIPLE
• Who Masked: PARTICIPANT, INVESTIGATOR, OUTCOMES ASSESSOR
• Purpose: OTHER
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Professor Christine Feinle-Bisset (Professorial Senior Research Fellow)

Study Record Dates

• First Submitted: June 2, 2025
• First Posted: June 10, 2025
• Study Start: June 28, 2025
• Primary Completion (Estimated): June 28, 2026
• Study Completion (Estimated): November 25, 2026
• Last Updated: June 24, 2025

Record last verified: 2025-06

Data Sharing

• IPD Sharing: Will not share

Locations

AU (1)