Dietary Quality and Microbiome Profiles among Rectal Cancer Patients: A Cross-Sectional Pilot Study

Examining whether gut microbial taxa abundances and predicted functional pathways correlate with dietary quality scores at the end of neoadjuvant chemoradiotherapy (nCRT) for rectal cancer (RC); identifying differentially abundant bacterial species from the pantothenate and acetyl-coenzyme A biosynthesis pathways that differ among dietary quality groups in a subset of participants.

RC patients (n = 30) provided stool samples for 16S rRNA gene sequencing. To validate pathway predictions from the 16S rRNA gene data, stool samples from a subset of 17 participants underwent shallow shotgun metagenomics sequencing (SMS). Dietary quality was calculated using the Prime Diet Quality Score (PDQS; 24-hour recall). 16S rRNA gene data were analyzed using QIIME2, and SMS data were analyzed using HUMAnN2.

At the genus level, Parvimonas, Caproiciproducens, and uncultured Eggerthellaceae abundances positively correlated (Spearman's rho = 0.36 to 0.50) with PDQS scores, whereas abundances of Prevotella, Rothia, Peptostreptococcus, Paeniclostridium, Enterococcus, and Howardella correlated negatively (Spearman's rho = -0.43 to 0.36). Predicted pathways, including those related to B-vitamin biosynthesis and enzyme cofactor biosynthesis (e.g., B5/pantothenate [phosphopantothenate biosynthesis I]), were correlated with higher PDQS scores. Mean abundances of species predicted to encode the vitamin B5-CoA pathway were greater in the high- diet-quality group.

Findings suggest important associations between the taxa abundances of gut bacteria and the abundances of predicted B-vitamin biosynthesis pathways and dietary quality at the end of nCRT. Three bacterial species encoding vitamin B5-CoA biosynthesis pathways were prominent in high-dietaryquality participants.