Dietary Gradient, Blastocystis Colonisation, and Gut Microbiota Ecology in Mexican University Students: An Exploratory Cross-Sectional Study

Gut microbiota is shaped by interactions among diet, host characteristics, and microbial colonisation. This exploratory cross-sectional study examined associations between a dietary gradient, Blastocystis colonisation, and gut microbiota in 41 university students, seven (17.1%) of whom were colonised with Blastocystis. Dietary intake was assessed using a validated food frequency questionnaire, and a diet-ratio was derived from the relative energy contribution of industrialised and non-industrialised foods. Gut microbiota was characterised by 16S rRNA gene sequencing. The multivariable model including diet-ratio, age, and body mass index was associated with microbiota structure in the primary genus-level analysis (PERMANOVA: R2 = 0.090, p = 0.041), although this association was attenuated after adjustment for abdominal pain and was not retained using the de novo DADA2 ASV table. Blastocystis colonisation was not associated with overall microbiota composition but was associated with greater alpha diversity (Shannon: p = 0.033; Gini–Simpson: p = 0.043). These alpha-diversity associations remained statistically significant after additional adjustment for abdominal pain and genus-level rarefaction, although they were less consistent in other sensitivity analyses. Genus-level associations with the dietary gradient did not remain significant after false discovery rate correction. No statistically significant diet-ratio × Blastocystis interaction was detected, although the small number of colonised participants limited assessment of effect modification. Overall, these findings suggest that dietary and Blastocystis-related associations may involve different ecological dimensions of the gut microbiota and warrant confirmation in larger studies.