CITIZEN science has established the feasibility of the Blue Muffin test as a potential population-level clinical biomarker for whole gut transit time (WGTT). This cross-sectional, citizen-generated data study, presented at UEGW 2026, also investigated WGTT and its associations with several anthropometric and physical performance measures.
Given the lack of real-time health measures in traditional public health surveillance, researchers devised the Blue Muffin test to measure WGTT and assess its feasibility as a population-level biomarker. They recruited 1,055 citizens through an open invitation to a two-day public event in Leuven, Belgium, where participants aged 6–81 years completed 14 standardised health assessment stations.
At the gastrointestinal station, participants answered six questions on habitual diet and bowel movement frequency before consuming a blue muffin containing a non-absorbable dye. They then reported when blue coloured stool was first observed and classified their stool form using the Bristol Stool Scale. WGTT was defined as the time between ingestion and the first appearance of blue stool.
Additional anthropometric and physical performance measures included waist circumference, body mass index (BMI), and handgrip strength, measured using a JAMAR hand dynamometer. Statistical tests assessed group differences, univariate associations, and multivariable relationships.
Of the 1,055 participants recruited, 831 completed the gastrointestinal assessment, with a median age of 49 years. Median WGTT was 23.9 hours, and 81.3% of participants fell within the data-derived normative range of 13.3–51.2 hours.
WGTT decreased with increasing stool looseness (p=2.6×10⁻²⁰), from a median of 45.4 hours for Bristol Stool Scale Type 1 to 18.4 hours for Type 7. Longer transit times were also associated with less frequent bowel movements (p=1.1×10⁻⁸). Females had significantly longer WGTT than males (25.9 vs 21.9 hours; p=9.9×10⁻⁶).
WGTT showed significant negative correlations with body mass index (BMI; Spearman’s rank correlation coefficient [r]=−0.11; adjusted p=5.8×10⁻³), waist circumference (r=−0.09; adjusted p=1.8×10⁻²), and handgrip strength (r=−0.15; adjusted p=5.2×10⁻⁵). In multivariable linear regression, age (regression coefficient [β]=0.005; p=0.001), sex (β=−0.156; p=0.009), and BMI (β=−0.004; p=0.047) remained significantly associated with WGTT, while handgrip strength did not (p=0.212). No significant associations were found between dietary habits and WGTT.
These findings support the Blue Muffin test as a potential population-level biomarker for WGTT, with associations observed across bowel habits, age, sex, and BMI.
Further research, including more detailed dietary assessments, is needed to validate the test, clarify the role of nutrition in gut transit, and inform personalised nutritional strategies.
Verstockt S et al. One blue muffin, thousand engaged: citizen science validates a clinical biomarker of gut transit time. Abstract OP241. UEGW Congress, 17-20 October 2026.
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