Abstract
Body mass index (BMI) is frequently used to investigate associations between gut microbiota and nutritional status in children, although it primarily reflects adiposity and may not fully capture broader aspects of physiological development. Height-for-age z-score (HAZ), an indicator of linear growth, may provide complementary information on microbiota-host interactions during childhood. This exploratory cross-sectional study investigated associations between anthropometric indicators and gut microbiota composition in a cohort of healthy Spanish school-aged children. Forty-five children aged 8-12 years were included. Faecal microbiota composition was analysed by 16S rRNA gene sequencing, and associations with anthropometric variables were evaluated using correlation and multivariable regression analyses. The gut microbiota was dominated by Bacillota and Bacteroidota, with limited variability in overall community structure across the cohort. BMI-for-age was not associated with microbial diversity, taxonomic composition or the Bacillota/Bacteroidota ratio. In contrast, HAZ was negatively associated with the Bacillota/Bacteroidota ratio, and this association remained significant after adjustment for BMI-for-age. No significant differences in alpha or beta diversity were detected according to anthropometric indicators. These findings suggest a possible relationship between linear growth and gut microbiota composition in healthy children. Given the limited sample size and cross-sectional design, the results should be considered exploratory and hypothesis-generating. Further studies are needed to confirm these observations and clarify the potential role of gut microbial ecology in childhood growth.