Optimizing blue poo: A validated, cost-effective method for measuring whole gut transit time

Whole gut transit time (WGTT) provides essential insights into gastrointestinal health, but traditional measurement methods are often expensive or invasive. This study optimizes and validates the "blue dye method," an affordable and minimally invasive approach to WGTT measurement. Using "Hollinger Farbpulver Blau" (containing food colors E131 and E132), dye concentrations ranging from 30 mg to 241 mg were tested across four modes of delivery: capsule with liquid, gummy bear, muffin, and capsule with rice crackers and liquid. Each presented limitations: capsules taken with liquid led to inconsistent transit times, gummy bears caused staining, and muffins were perishable. Measured WGTTs varied between 18 and 29 h depending on the mode of delivery and dye concentration. Optimal protocol was a capsule containing 60 mg of dye taken with two rice crackers and liquid, ensuring accurate detection without practical inconveniences. The standardized and optimized blue dye method provides valid WGTT measurements, making it well suited for large-scale population studies and clinical applications. Uses a simple blue dye as a marker for gut transit. Tested several modes of delivery and concentrations to find the most practical option. Established a standardized protocol for reliable and reproducible measurement.