Nourishing the Microbiome at Preschool age: Dietary influences from infancy to present

Nourishing the Microbiome at Preschool age:  

Dietary influences from infancy to present 

Anne Salonen  

Diet is a key driver of the gut microbiota composition and diversity throughout the lifespan.  

In infancy, the gut microbiota development follows largely predictable patterns of maturation shaped by early exposures, such as birth mode, exposure to intrapartum antibiotics and breastfeeding (Fahur et al., 2025). During the first 6 months of life, exclusive breastfeeding is associated to lower gut microbiota diversity and higher relative abundance of bifidobacteria, while formula feeding associates to earlier and higher microbiota diversity and maturity (Ho et al., 2018). Formula feeding promotes infant gut microbiota maturity by increasing Bacteroidetes and adult type Clostridia that otherwise become abundant only after the introduction of (plant-based) solid foods.  

Mixed feeding is common in infants, but very little is known about how partial breastfeeding, and especially the variations in the timing, frequency, proportions of formula supplementation affect the infant gut microbiota development. Most infant microbiota studies have not recorded early diet in sufficient granularity to address these questions. In the Finnish Health and Early Life Health (HELMi) birth cohort (NCT03996304), we collected extremely frequent data on diet in initially 1151 infants: Weekly until the age of four months, then biweekly until 7 months, and monthly until 12 months. As many as 95% of the infants were breastfed at age of 3 months and 70% still at 12 months (Jokela et al., 2023). Altogether 44% reported formula use at least once. Our unpublished data based on unsupervised clustering of the reported volume and frequency of formula use, derived from the mean of 14.8 weekly reports from 1023 families with ≥ 8 reports from birth to age of 17 weeks, reveals three main patterns of formula use during the neonatal period: Limited to the first days or weeks after birth, occasional and scattered over the follow-up, and supplementation that starts or increases along the growth and advancing age of the infant.  

Next, these patters will be studied for their effects on infant gut microbiota development, with major potential for informing tailored feeding guidelines and scientific basis for the development of stage-specific formulas or microbiota-supporting supplements. 

The transition from milk-based diet to solid foods in infancy is probably the most drastic dietary change in humans. This transition offers an interesting opportunity to study dietary influence on the gut microbiota. Somewhat surprisingly, composition of infant gut microbiota is more pronouncedly influenced by the cessation of breastfeeding than introduction of the solid foods (Bäckhed et al., 2015 and other more recent studies). We addressed the effect of continued breastfeeding and time since starting solids on the 2^nd year of life in the HELMI cohort. Interestingly, breastfeeding had a statistically significant effect of child microbiota still at 18 months, with a larger effect size than early or late start of the solids (Jokela et al., 2023). Collectively, these results suggests that early nutrition have lasting effects on gut ecosystem development, and overall underscore the potential for early dietary exposures to shape developmental trajectories with implications for later health. 

While infant and adult gut microbiota and their dietary determinants are relatively well understood, the preschool age remains under-studied despite continued gut microbiota development and maturation (Roswall et al., 2021). We analysed food frequency questionnaires and gut microbiota compostion and functionality from 336 HELMI children at 4-5 years of age. Top genera in the gut microbiota of Finnish preschoolers included Faecalibacterium, Agathobacter, Bacteroides, Bifidobacterium and Ruminococcus. Our preliminary results indicate that consumption of unhealthy foods, especially salty snacks, contribute to the main differences in diet in this age group. Considering the gut microbiota, the proportion of variation attributable to breastfeeding history appears comparable or even larger than the current diet assessed with FFQ.    

 References