To determine whether there is an association between the inflammatory potential of the diet, measured by the dietary inflammatory index (DII®), and the composition of intestinal microbiota in adults with functional constipation (FC).

A cross-sectional study was carried out with 68 adults with FC. Energy-adjusted DII (E-DII) was calculated from data obtained from food surveys, serum inflammation markers were measured and the composition of the intestinal microbiota was evaluated using the 16S rRNA gene sequencing method. Participants were assigned into two groups: anti-inflammatory diet (AD: E-DII < 0) and pro-inflammatory diet (PD: E-DII ≥ 0). Associations of E-DII scores with microbial diversity and composition were examined using differences between the E-DII groups and linear and hierarchical regression.

E- DII was inversely correlated with relative abundance of Hungatella spp. and Bacteroides fragilis and positively correlated with Bacteroides thetaiotaomicron and Bacteroides caccae (p < 0.05). B. fragilis was positively correlated with IL-10. The AD group had higher relative abundances for the genus Blautia and Hungatella, lower abundances of Bacteroides thetaiotamicron and Bacteroides spp. (p < 0.05), as well as higher frequency of evacuation (p = 0.02) and lower use of laxatives (p = 0.05). The AD group showed a reduction in the abundance of Desulfovibrio spp. and Butyrivibrio, Butyrivibrio crossotus, Bacteroides clarus, Bacteroides coprophilus and Bacteroides intestinalis (all p < 0.05). The greater abundance of Bacteroides clarus increased the individual's chance of performing a manual evacuation maneuver.

Therefore, the results of this study demonstrated that the inflammatory potential of the diet is associated with the gut microbiota in individuals with FC.