Could similar gut symptoms hide different biological stories?
Two people can have very similar bowel symptoms, but are the same biological processes at work? Irritable bowel syndrome (IBS), functional constipation and functional diarrhoea are typically grouped by symptoms, even though people with the same diagnosis may respond differently to treatment. A New Zealand research team asked whether looking at the microbiome alongside other biological signals could uncover differences that symptom labels miss.
Researchers analysed data from 300 adults, including healthy controls and people with these lower-gut conditions. They combined symptom questionnaires with shotgun metagenomic profiling of stool samples and measurements of metabolites in stool and blood. Using machine learning, they searched for patterns that grouped participants by both their reported symptoms and biology, rather than relying on their existing diagnoses alone.
The combined analysis identified 11 clusters, eight of which were stable during internal testing. These groups did not map neatly onto familiar IBS or constipation categories. One subgroup with substantial gastrointestinal pain showed changes in microbial pathways and blood metabolites suggesting altered nitrogen and ammonia handling. Other patterns included reduced microbial richness and differences in pathways involved in nutrient metabolism, even in participants with a comparatively lower symptom burden. In other words, similar symptoms did not necessarily point to the same biological profile.
The findings suggest a possible reason why people with the same diagnosis do not always respond to treatments in the same way. However, this was a cross-sectional, observational study, and the clusters were only weakly separated overall. Larger, longitudinal studies will be needed to determine whether these differences are reproducible over time or useful for guiding care. For now, the study highlights the potential value of looking beyond symptoms alone – towards the gut microbiome, its functional potential and its interactions with the wider body.
