Gut physiology and environment explain variations in human gut microbiome composition and metabolism.

The human gut microbiome is highly personal. However, the contribution of gut physiology and environment to variations in the gut microbiome remains understudied. Here we performed an observational trial using multi-omics to profile microbiome composition and metabolism in 61 healthy adults for 9 consecutive days. We assessed day-to-day changes in gut environmental factors and measured whole-gut and segmental intestinal transit time and pH using a wireless motility capsule in a subset of 50 individuals. We observed substantial daily fluctuations, with intra-individual variations in gut microbiome and metabolism associated with changes in stool moisture and faecal pH, and inter-individual variations accounted for by whole-gut and segmental transit times and pH. Metabolites derived from microbial carbohydrate fermentation correlated negatively with the gut passage time and pH, while proteolytic metabolites and breath methane showed a positive correlation. Finally, we identified associations between segmental transit time/pH and coffee-, diet-, host- and microbial-derived metabolites. Our work suggests that gut physiology and environment are key to understanding the individuality of the human gut microbial composition and metabolism.