The speed at which waste moves through your digestive system, whether rapidly or leisurely, might have more significant effects on your health than initially apparent.
A 2023 review analyzing data from numerous studies reveals notable differences between the gut microbiomes of individuals with fast and slow digestive transit times.
Given the crucial role of the gut microbiome in health, these findings could have previously overlooked implications.
Specifically, slow digestive transit and constipation are associated with metabolic and inflammatory disorders, and even neurological conditions like Parkinson’s disease.
Identifying microbiome profiles linked to these transit times could pave the way for new treatments and management strategies for these conditions.
“By considering both individual and within-individual variations in gut transit time, we can enhance our understanding of diet-microbiota interactions and disease-related microbiome patterns,” state nutritionists Nicola Procházková and Henrik Roager from the University of Copenhagen in their report.
“A comprehensive understanding of the complex, bidirectional interactions between gut microbiota and transit time is essential to grasp variations in gut microbiomes concerning health and disease.”
The gut microbiome’s composition and activity are crucial to health, influenced by factors such as exercise, diet, and disease.
Procházková and her team explored whether the duration that gut microbes interact with waste before excretion might affect gut health.
The researchers utilized existing data on participants’ gut transit times, stool consistency (as a proxy for transit time), dietary habits, microbiome composition, and metabolite production.
Their findings, encompassing thousands of patients with and without conditions like irritable bowel syndrome, constipation, and liver cirrhosis, highlight the complexity of understanding gut transit time.
Determining gut transit time can require advanced methods, such as ingestible capsules with sensors that track their digestive journey.
Another tool is the Bristol Stool Scale, which visually categorizes stool consistency from hard pellets (indicating long transit time) to watery mush (indicating short transit time). Some studies use markers like blue dye or sweet corn to track the time taken to pass through the digestive system.
The aim is to estimate the duration food remains in the colon. A longer stay gives bacteria more time to ferment contents, regulate acidity, and produce health-impacting metabolites.
The analysis revealed intriguing results: individuals with faster transit times had distinctly different microbiomes from those with slower transit times. Including transit time data improved predictions of gut microbiota compared to diet analysis alone.
Those with quicker transit typically had microbiomes dominated by fast-growing species thriving on high-carbohydrate, low-fat diets. Conversely, slower transit times often correlated with microbiomes thriving on protein-rich diets.
Both extremes exhibited lower microbiome diversity than those with average transit times, suggesting that varying transit speeds foster environments favoring certain species.
This creates a feedback loop where dominant species release metabolites that sustain their favorable environment.
Overall, these findings suggest that gut transit time is a crucial yet often overlooked factor in understanding gut functionality, its impact on health, and patients’ responses to treatments like probiotics.
Related: Your Poop Schedule May Be Shaping Your Body From The Inside Out
This could explain why standardized gut health advice might not work universally, as individuals processing the same meal at different speeds can experience varied results.
Transit times may also affect the body’s response to probiotics, supplements, or medications interacting with the gut. Understanding a patient’s gut rhythm could lead to more personalized treatment and dietary recommendations.
“By incorporating gut transit time measurements in studies related to the gut microbiome, we can deepen our understanding of the connections between the microbiome, diet, and disease,” the researchers state in their paper.
“These insights may be pivotal for preventing, diagnosing, and treating various diseases within and outside the gut throughout life.”
The study was published in 2023 in the journal Gut.
An earlier version of this article was published in December 2025.
