Imbalance in Gut Bacteria May Play Critical Role in Obesity Development


A new analysis found differences in the gut bacteria seen in adults with obesity, suggesting that changes in the gut microbiota that predispose to adult obesity may begin in early childhood.

Gaël Toubon | LinkedIn

Gaël Toubon

Credit: LinkedIn

The make-up and volume of gut bacteria in toddlers at age 3.5 may be predictive of overweight based on body mass index (BMI) at 5 years old, regardless of whether they are born prematurely, according to new research.1

The analysis, presented at the 2023 European Congress on Obesity (ECO), identified differences in the bacteria that colonize the gut observed in adults with obesity, indicating that changes in the gut microbiota that predispose to adulthood obesity begin in early childhood.

“The gut microbiota is emerging as an important early-life factor able to influence weight gain in childhood and later life,” Gaël Toubon from Inserm at Université Paris Cité and Université Sorbonne Paris Nord, said in a statement.1 “Our findings reveal how an imbalance in distinct bacterial groups may play an important role in the development of obesity.”

As the composition of the gut microbiota evolves and changes in the first few months and years of life, disruption to its development is associated with conditions in later life, including inflammatory bowel disease, diabetes, and childhood obesity.2 Yet, the associations between gut microbiota and changes in BMI during childhood and pediatric overweight remain unclear, and data on preterm infants remains limited.

To better understand these associations, Toubon and colleagues investigated how the gut microbiota of children at 3.5 years from 2 nationwide birth cohorts in France was associated with their BMI at 5 years old and changes in their BMI between 2 and 5 years old. Adjustments for confounding factors were performed, including child age and sex, gestational age, delivery mode, breastfed status, maternal preconception BMI, and country of birth.

A total of 143 preterm infants (born ≤32 weeks of gestational age) were included from the national EPIPAGE2 study conducted in all maternity and neonatal units in France in 2011 and a total of 369 full-term infants (born ≥33 weeks of gestational age) from the national ELFE study tracking 18,000 children born in metropolitan France in 2011. Investigators collected stool samples from infants at 3.5 years.

Upon analysis, genetic microbiota profiling suggested a positive association between BMI z-score at 5 years and the ratio of gut bacteria Firmicutes to Bacteroidetes that are directly involved with obesity. More Bacteroidetes, compared to Firmicutes, were associated with greater leanness in individuals. Investigators noted these gut bacteria affect weight due to regulating how much fat an individual can absorb.

“Children with a higher ratio of Firmicutes to Bacteroidetes will absorb more calories and be more likely to gain weight,” Toubon said.1

Moreover, the analysis found that 6 types of gut bacteria were highly predictive of BMI z-score at 5 years old. Data showed greater abundances of 3 categories of bacteria (Eubacterium hallii group, Fusicatenibacter, and Eubacterium ventriosum group) were identified as a risk factor for a higher BMI z-score. Meanwhile, greater numbers of 3 types of bacteria (Eggerthella, Colidextribacter, and Ruminococcaceae CAG-352) were associated with a lower BMI z-score.

The investigative team found some bacterium types were associated with changes in BMI z-scores between 2 and 5 years old, suggesting that some were involved in a higher speed of progression in BMI z-scores between 2 and 5 years old and others were more protective against faster progression.

The analysis additionally showed that both the predicted biosynthesis of steroid hormones and the biotin gut microbiota metabolic pathways were associated with a lower 5-year BMI z-score. Being born prematurely made no difference to later BMI, according to investigators. Toubon noted that the gut microbiota is not only affected by which bacteria are involved, but what they are doing.

“Further research is needed to drill down into the specific bacterial species that influence risk and protection and to better understand when the switch to an obesity-favorable gut microbiota may take place, and therefore the right timing for possible interventions,” Toubon said.1


  1. Easoobesity. A toddler’s gut bacteria predict whether they will be overweight at 5 years old. EurekAlert! May 19, 2023. Accessed May 23, 2023.
  2. Geng J, Ni Q, Sun W, Li L, Feng X. The links between gut microbiota and obesity and obesity related diseases. Biomed Pharmacother. 2022;147:112678. doi:10.1016/j.biopha.2022.112678
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