The link between obesity and the oral and gut microbiota is well established in adults and adolescents, but is not well studied in children. A new paper published in Scientific Reports aimed to redress this imbalance, and found that the composition of the oral microbiota is associated with weight trajectories over the first 2 years of life.

“Together with our co-author paediatrician Ian Paul, we have been following a cohort of almost 400 children from their birth to the age of 3 years as part of the INSIGHT study,” explains author Kateryna Makova. Some parts of the INSIGHT study have focused on the behavioural and dietary variables that influence the development of obesity, while the present paper focused on characterizing the oral and gut microbiota.

The researchers analysed oral and stool samples from ~200 children and measured weight and length at seven time points. “We used functional data analysis to analyse childhood weight-gain trajectories longitudinally,” says author Matthew Reimherr. In children who gained weight rapidly, bacterial diversity was decreased and the Firmicutes to Bacteroidetes ratio was increased in the oral microbiota, but not the gut microbiota. This pattern is known to occur in the gut microbiota of adults with obesity, so the finding suggests that an obesity-associated microbiota composition is established in the oral microbiota before it becomes established in the gut microbiota. “The links we were able to demonstrate between oral microbiota and weight gain are novel, and could lead to non-invasive clinical screens to identify children at a particular risk of obesity, who would be candidates for early preventive interventions,” says author Francesca Chiaromonte.

The team are now planning to expand their study, including analyses of the siblings and mothers of the original cohort. “Expanding the study will allow us to have a fuller understanding of early life microbiota development and how that influences child growth,” concludes author Sarah Craig.