A Study on Gastrointestinal Transit Time at the Population Level (GITTPop)

Gastrointestinal Transit Time at the Population Level: A Cross-sectional Study

The goal of this study is to investigate the baseline of gastrointestinal transit time (GITT) and explore its relationship with other health indicators in 932 healthy adult volunteers.

The main questions it aims to answer are:

What are the population-level baseline values for GITT using the blue dye method? How is GITT associated with key physiological parameters including blood metabolic markers, life style, and stool characteristics?

Participants will:

Consume a standardized blue dye muffin after overnight fasting at the research center; Offer a finger prock blood samples for metabolic profiling; Collect stool samples for moisture measurement; Complete detailed questionnaires on diet, lifestyle, and bowel habits; Record the time of first blue stool appearance to determine GITT.

Study Overview

• Status: Not yet recruiting
• Conditions: Gastrointestinal Transit Time
• Intervention / Treatment: Other: Diet

Detailed Description

This explorative study is designed as a cross-sectional investigation aimed at establishing population-level reference values for gastrointestinal transit time (GITT). Adult participants from the general population will undergo GITT measurement using the blue-dye method. This muffin contains blue colorant that cannot be absorbed; after ingestion, it passes through the entire gastrointestinal tract and is eventually excreted in feces. Following a two-day lifestyle standardization period (including dietary and activity guidance) to minimize potential confounding effects on gastrointestinal motility, participants will attend a clinical visit where they will ingest a blue muffin. GITT will be determined by measuring both the time interval between ingestion of the blue muffin and the first appearance of blue-colored stool, and the duration from its first appearance to its complete disappearance.

The blue muffin method has been well-established in previous research for GITT assessment. Building upon the methodology developed by Berry et al., we will introduce stricter pre-test condition controls (includes dietary advice and lifestyle recommendations) and optimized the blue muffin formulation.These improvements allow for reliable measurement with a single muffin administration, which has been evaluated through KU Leuven Health Pass in a large sample size(S-70168).

To investigate potential determinants and correlates of GITT, we will collect biochemical parameters, fecal moisture, and resting metabolic rate. Additionally, participants will complete 24-h diet record and health questionnaires assessing bowel movement, physical activity habits, stress levels, sleep quality and hydration condition for subsequent correlation analyses.

• Study Type: Observational
• Enrollment (Estimated): 932

Contacts and Locations

• Study Contact: Name: Christophe Matthys; Phone Number: +32 016342655; Email: christophe.matthys@uzleuven.be
• Study Contact Backup: Name: Wei Li; Phone Number: +32 016344539; Email: wei.li2@kuleuven.be

Study Locations

• Belgium
  • Flemish Brabant
    • Leuven, Flemish Brabant, Belgium, 3000
      • Department of Chronic Diseases and Metabolism
      • Contact: Wim Janssens; Phone Number: +32 016252111; Email: wim.janssens@kuleuven.be
      • Contact: Evelyne van Etten; Phone Number: +32 016330855; Email: evelyne.vanetten@kuleuven.be

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Healthy volunteers from the Flanders region who volunteered to participate in the research

Description

Inclusion Criteria:

1. 18-65 years old
2. 18.5 kg/m² ≤ BMI ≤ 25 kg/m² or BMI ≥ 30 kg/m² (people with normal weight or obesity)
3. Provision of informed consent to participate.

Exclusion Criteria:

1. Gastrointestinal conditions which may affect nutrient absorption or gastric emptying, including coeliac disease, Crohn's disease, previous resection of the small intestine other than bariatric surgery, gastroparesis;
2. Using medications which effect gastric motility (e.g., domperidone, erythromycin, metoclopramide, prucalopride, opiates, loperamide, …)
3. The ingredients of blue muffins include gluten, nuts, baking powder, sugar, vanilla extract and sunflower oil. Participants with allergies to these ingredients;
4. Current diagnosis of cancer;
5. Advanced organ failure, including chronic kidney disease Stage 5, liver cirrhosis Child-Pugh B or C, intestinal failure, heart failure stage D, or chronic obstructive pulmonary disease stage 4;
6. Immobility;
7. Neuromuscular degenerative conditions associated with muscular atrophy, such as myasthenia gravis, muscular dystrophies, fibromyalgia, or multiple Sclerosis;

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Adult participants; Healthy adult participants without serious gastrointestinal diseases	Other: Diet; Participants will consume a regular muffin containing blue dye

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Gastrointestinal transit time	Calculate the transit time by the recorded muffin consuming time, first blue stool appearance time and last blue stool appearance time	From enrollment to the end of study at 2 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Height (cm)	Measured using a height meter, in centimeters.	baseline
Weight (kg)	Measuring using a scale, in kg.	baseline
BMI	weight and height will be combined to report BMI in kg/m^2	baseline
Blood glucose (mmol/L)	Measure blood glucose by CardioChek Plus in mmol/L	baseline
Fat mass (kg)	Using Bodystat quadscan 4000 to measure fat mass (kg)	baseline
Lean body mass(kg)	Using Bodystat quadscan 4000 to measure lean body mass (kg)	baseline
Fat percentage (%)	Using Bodystat quadscan 4000 to measure fat%	baseline
Total cholesterol (mmol/L)	Measuring by Mission cholesterol Meter in mmol/L	baseline
HDL-C (mmol/L)	Measuring by Mission cholesterol Meter in mmol/L	baseline
LDL-C (mmol/L)	Measuring by Mission cholesterol Meter in mmol/L	baseline
Triglyceride (mmol/L)	Measuring by Mission Cholesterol Meter in mmol/L	baseline
Food record	Participants record their 24-h diets through smartphone application	2 days after study
Stool form	Stool form will be evaluated by Bristol Stool Form Scale, the score is from 1 to 7, with values closer to the middle indicating more ideal stool shape.	baseline
Hydration status	Hydration status will be rated from 1 to 8 by Urine color chart, with higher numbers indicating that the body needs more water.	baseline
Perceived level of stress	The10-item Perceived Stress will be used to measures an individual's perceived level of stress over the past month. The total score ranges from 0 to 40. A higher score indicates a greater perceived level of stress.	baseline
Sleep quality	Pittsburgh Sleep Quality Index will be used to assess subjective sleep quality over the past month. The total score ranges from 0 to 21. A higher score indicates poorer sleep quality.	baseline
Activity level	The Baecke Physical Activity Questionnaire will be used to assess daily habitual physical activity, with a particular focus on work-related and exercise-related activities. It does not produce a single total score, but rather scores on three dimensions, each typically ranging from 1 to 5. On each dimension, a higher score indicates a higher level of physical activity in that area. Therefore, for assessing activity levels, a higher score is generally better.	baseline

Collaborators and Investigators

• Sponsor: KU Leuven

Study record dates

Study Major Dates

• Study Start (Estimated): December 1, 2025
• Primary Completion (Estimated): December 30, 2026
• Study Completion (Estimated): December 30, 2026

Study Registration Dates

• First Submitted: November 17, 2025
• First Submitted That Met QC Criteria: December 15, 2025
• First Posted (Actual): December 30, 2025

Study Record Updates

• Last Update Posted (Actual): December 30, 2025
• Last Update Submitted That Met QC Criteria: December 15, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: Gastrointestinal motility; Reference value; Baseline study
• Additional Relevant MeSH Terms: Diet, Food, and Nutrition; Physiological Phenomena; Nutritional Physiological Phenomena; Diet
• Other Study ID Numbers: S70908

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No