DUBLIN ― Gut microbiota, including species type and diversity, in children at age 3.5 years is associated with a higher body mass index (BMI) at age 5, and BMI changes between ages 2 and 5 reflect those seen in adults with obesity, shows a study presented at this year’s European Congress on Obesity (ECO) 2023.

No interaction was found with preterm birth status in the study, which was conducted by Gaël Toubon, a PhD student at Inserm, Université Paris Cité and Université Sorbonne Paris Nord, Paris, France, and colleagues.

“Our findings reveal how an imbalance in distinct bacterial groups may play an important role in the development of obesity,” Toubon said. “We found that some microbiota characteristics at 3.5 years were associated with BMI at 5 years and speed of progression of BMI between 2 and 5 years.”

The study shows that “the microbiota seen in an obesity phenotype in adults are already present in early childhood, suggesting that gut microbiota is a cause rather than a consequence of an obesity phenotype,” he added. “Differences in microbiota are observed before the onset of overt obesity and metabolic complications.”

More studies are needed in the pediatric population “to better understand when the switch to an obese-like gut microbiota may take place and, therefore, the right timing for possible interventions,” Toubon said.

Microbiota-BMI Link Investigated

The study aimed to understand whether the gut microbiota of children at age 3.5 years is associated with BMI at age 5, and whether preterm birth or term birth makes a difference, as suggested by other studies.

“The gut microbiota is a potential critical early-life factor able to influence long-term health; however, the relationship between the gut microbiota and change in childhood BMI is unclear,” Toubon said.

According to the WHO European Regional Obesity Report 2022, from the World Health Organization, one third of preschool children in Europe are living with overweight or obesity, he noted.

The study included 143 children and another 369 children from two general population birth cohorts, the EPIPAGE2 (preterm infants born less than 32 weeks of gestational age) and ELFE (infants born over 33 weeks’ gestational age) respectively. whose stool samples were collected at age 3.5 years.

Genetic profiling of gut microbiota was carried out and associations were explored with BMI z-scores (measures of relative weight adjusted for child age and sex) at ages 3.5 and 5, as well as the change between ages 2 and 5.

Researchers assessed species diversity generally and the ratio of Firmicutes to Bacteroidetes species because, by implication, the more Bacteroidetes (compared to Firmicutes) present in the gut, the leaner individuals tend to be.

Adjustments were made for confounding factors, including child age and sex, gestational age, delivery mode, ever breastfed, maternal preconception BMI, and country of birth. Toubon and colleagues also identified specific genera and inferred functional metabolic pathways associated with change in BMI z-score.

Bacteria Ratios Play a Role

The researchers found a positive association between the ratio of Firmicutes to Bacteroidetes and a higher BMI-z score at age 5.

Additionally, at age 5, the presence of some genera was highly predictive of BMI z-score and showed a linear relationship such that greater abundances of Eubacterium hallii group, Eubacterium ventriosum group, and Fusicatenibacter were associated with a higher BMI z-score, while greater abundances of Eggerthella, Colidextribacter, and Ruminococcaceae CAG-352 were associated with a lower BMI z-score.

“The reason these gut bacteria affect weight is because they regulate how much fat we absorb,” Toubon said. “Children with a higher ratio of Firmicutes to Bacteroidetes will absorb more calories and be more likely to gain weight, and it is seen in the adult population too.”

Analysis of the change in BMI-z scores between ages 2 and 5 years showed that specific genera were associated with a faster increase in BMI z-score, while other bacteria were more protective against a BMI-z score increase.

There was no interaction with preterm status in any of the described relationships, the researchers note.

“In addition, we demonstrated that the steroid hormone biosynthesis and the biotin gut microbiota metabolic pathways were associated with a lower BMI z-score at age 5 years,” Toubon said.

“These findings suggest that what matters with the gut microbiota is not only a question of which bacteria are involved but also what they are doing,” Toubon explained.

There is a need for further research to drill down into the specific bacterial species that influence risk and protection, he added.

Toubon reports no relevant financial relationships.

European Congress on Obesity (ECO) 2023: Abstract PO3.012.

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