Is stool frequency associated with the richness and community composition of gut microbiota?

BACKGROUND/AIMS: Recently, a number of studies have reported that the gut microbiota could contribute to human conditions, including obesity, inflammation, cancer development, and behavior. We hypothesized that the composition and distribution of gut microbiota are different according to stool frequency, and attempted to identify the association between gut microbiota and stool frequency. METHODS: We collected fecal samples from healthy individuals divided into 3 groups according to stool frequency: group 1, a small number of defecation (≤2 times/wk); group 2, normal defecation (1 time/day or 1 time/2 day); and group 3, a large number of defecation (≥2–3 times/day). We evaluated the composition and distribution of the gut microbiota in each group via 16S rRNA-based taxonomic profiling of the fecal samples. RESULTS: Fecal samples were collected from a total of 60 individuals (31 men and 29 women, aged 34.1±5.88 years), and each group comprised 20 individuals. The microbial richness of group 1 was significantly higher than that of group 3 and tended to decrease with increasing number of defecation (P<0.05). The biological community composition was fairly different according to the number of defecation, and Bacteroidetes to Firmicutes ratio was higher in group 1 than in the other groups. Moreover, we found specific strains at the family and genus levels in groups 1 and 3. CONCLUSIONS: Bacteroidetes to Firmicutes ratio and the abundance of Bifidobacterium were different according to the stool frequency, and specific bacteria were identified in the subjects with large and small numbers of defecation, respectively. These findings suggest that stool frequency might be associated with the richness and community composition of the gut microbiota.