How the blue dye fared
The researchers analyzed data from 866 twins and unrelated adults from the United States and the United Kingdom who were enrolled in the PREDICT 1 study, which quantified metabolic responses to standardized meals. Participants underwent fasting and then ate two blue muffins, along with a glass of chocolate milk, then logged the first sign of blue coloring in their stool using an app. Participants also answered a questionnaire detailing the frequency and consistency of bowel movements. The researchers also conducted sequencing of stool samples to determine microbiome profile.
There was a strong correlation between stool consistency and frequency, as well as microbial diversity and the composition of the gut microbiome. The dye measurement identified different fast and slow transit time clusters (area under the receiver operating characteristic curve, 0.82), which were associated with the composition of the gut microbiome, including species like Akkermansia muciniphila, Bacteroides species, and Alistipes species (false discovery rate–adjusted P values < .01). Transit times measured with the blue dye was a better predictor of gut function than either stool consistency and stool frequency, suggesting that the dye may be a more useful method for large cohorts of healthy individuals.
Although associations with diet and cardiometabolic factors were more modest, longer transit times appear predictive of greater visceral fat and higher postprandial responses, “which are key measures of health.”
The authors cited some limitations, including the fact that the blue-dye method has not yet been compared with other transit methodologies. However, the gut transit time in this study was found to be strongly correlated with stool consistency and frequency.
“To conclude, our findings indicate that the blue dye method is a novel, inexpensive and scalable method of gut transit assessment providing valuable gut health and metabolic insights,” they wrote. “Its wide use in both research and clinical settings could facilitate the advancement of our understanding of gut function and its determinants, as well as the complex interactions between gut physiology and health outcomes.”
The study authors received funding from a wide range of nonindustry sources. Dr. Roager had no relevant financial disclosures.