Association between gut microbiota at 3.5 years of age and body mass index at 5 years: results from two French nationwide birth cohorts

Background/objectives The relationship between gut microbiota and changes in body mass index (BMI) or pediatric overweight in early life remains unclear, and information regarding the preterm population is scarce. This study aimed to investigate how the gut microbiota at 3.5 years of age is associated with (1) later BMI at 5 years, and (2) BMI z-score variations between 2 and 5 years in children from two French nationwide birth cohorts. Subjects/methods Bacterial 16S rRNA gene sequencing was performed to profile the gut microbiota at 3.5 years of age in preterm children ( n = 143, EPIPAGE 2 cohort) and late preterm/full-term children ( n = 369, ELFE cohort). The predicted abundances of metabolic functions were computed using PICRUSt2. Anthropometric measurements were collected at 2 and 5 years of age during medical examinations or retrieved from children’s health records. Statistical analyses included multivariable linear and logistic regressions, random forest variable selection, and MiRKAT. Results The Firmicutes to Bacteroidetes (F/B) ratio at 3.5 years was positively associated with the BMI z-score at 5 years. Several genera were positively ( [Eubacterium] hallii group, Fusicatenibacter , and [Eubacterium] ventriosum group ) or negatively ( Eggerthella, Colidextribacter , and Ruminococcaceae CAG-352 ) associated with the BMI z-scores at 5 years. Some genera were also associated with variations in the BMI z-scores between 2 and 5 years of age. Predicted metabolic functions, including steroid hormone biosynthesis, biotin metabolism, glycosaminoglycan degradation, and amino sugar and nucleotide sugar metabolism, were associated with lower BMI z-scores at 5 years. The unsaturated fatty acids biosynthesis pathway was associated with higher BMI z-scores. Conclusions These findings indicate that the gut microbiota at 3.5 years is associated with later BMI during childhood, independent of preterm or term birth, suggesting that changes in the gut microbiota that may predispose to adult obesity begin in early childhood.