In Saudi Arabia, those who have been diagnosed with CRC at a late stage were included in this study to investigate the gut microbial profile and its association to diet. This study also examines the risk factors for CRC in Saudi Arabia, focusing on diet quality, consumption of fruits and vegetables, and fat intake (total fat, saturated fat, monounsaturated fat, polyunsaturated fat, fat from plant food sources, and fat from animal sources). It also examines the role of dysbiosis in the gut microbiota and its potential link to the development of CRC.
Colorectal cancer (CRC) is a significant global health concern. Studies on the intestinal microbiota have demonstrated the important role that gut bacteria play in many cancers, particularly CRC. This study aims to assess the risk factors for CRC, particularly, diet quality and fat intake, as well as the role of dysbiosis in the gut microbiota and its potential link to the development of CRC in Saudi Arabia.  In this study, a cohort of 25 CRC patients diagnosed at late stage III and IV were enrolled. The diet quality and fat intake of participants included in this study was assessed using a modified version of the short-form food frequency questionnaire (SFFFQ) and a modified version of a food frequency questionnaire (FFQ) previously employed, respectively. To investigate the variety of fecal bacteria, 16S ribosomal RNA gene sequencing was employed, followed by clustering analysis. Simple linear regression was used to assess the association between diet quality and fat intake with the most abundant bacteria in CRC In order to find enriched pathways among the two groups, the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Cluster of Ortholog Genes (COG) functional annotation were utilized.  The findings showed the two groups' fecal microbiotas varied significantly in beta diversity. According to genera abundance of CRC compared to healthy participants, CRC was found to have enriched populations of Streptococcus, Lactobacillus, Klebsiella, Intestinibacter, Ralstonia, Alistipes, Pseudomonas, Peptostreptococcus, Faecalibaculum, Dubosiella, Erysipelatoclostridium, Enterobacter, Sellimonas, Lachnoclostridium, Eubacterium, Clostridium innocuum group, Aerococcus, Family_XIII_AD3001 Group, and Veillonella (p<0.05). Only Alistipes sp. was found to be positively linked to poor diet quality in CRC patients (p= 0.029; R-square= 0.47). According to the function and pathway prediction, the CRC group was linked to amino acid transport, signaling and metabolism, membrane biogenesis, DNA replication and mismatch repair system, and protease activity. These results suggested that the imbalance of intestinal bacteria and the elevated level of the predicated functions and pathways may contribute to the development of advanced CRC tumors. Further research is warranted to elucidate the exact role of the gut microbiome in colorectal cancer and its potential implications for diagnostic, prevention and treatment strategies.