Dietary Fibre Intake, Gut Microbiota, and Colorectal Health Biomarkers in Urban and Rural Cohorts in South West Nigeria

Dietary fibre exerts significant effects on gut microbiota composition and colorectal health through fermentation-derived short-chain fatty acids and modulation of intestinal epithelial integrity, but mechanistic evidence from African populations with distinct fibre intake levels and gut microbiota profiles is virtually absent. This study examines the relationship between dietary fibre intake, gut microbiota diversity and composition, and colorectal health biomarkers in comparative urban and rural cohorts in South West Nigeria. A cross-sectional comparative design enrolled 400 adults aged 30 to 60 years from Lagos Island as the urban cohort and Abeokuta rural settlements as the rural cohort. Habitual dietary fibre intake was assessed using a validated semi-quantitative food frequency questionnaire, with fibre values obtained from a Nigerian food composition database supplemented by laboratory analysis of local food items. Gut microbiota composition was characterised using shotgun metagenomic sequencing of stool samples. Colorectal health biomarkers measured from faecal samples included short-chain fatty acid concentrations, faecal calprotectin as an inflammation marker, and DNA integrity index as a surrogate of colon epithelial cell health. Serum lipopolysaccharide-binding protein was measured as a systemic gut barrier integrity marker. Structural equation modelling examined whether microbiota composition mediates the relationship between dietary fibre intake and colorectal biomarkers, adjusting for age, sex, body mass index, physical activity, and antibiotic use history. This study will produce the first Nigerian data on diet-microbiome-colorectal health relationships, contributing to the emerging African gut health research agenda. Keywords: dietary fibre, gut microbiota, colorectal health, metagenomics, South West Nigeria.