Frequently aired television commercials have made it clear that one's gut flora, the microbes that live in the digestive tract, aids digestion and keeps things moving regularly. What isn't so widely broadcast is the immune-strengthening benefit of these same microbes. Infants begin developing their gastrointestinal microbiomes at birth by way of their mother's milk during breastfeeding. Their own little bodies take over production of these important microbiotas once breastfeeding ends. The development of these microbiota continues for three years and benefits greatly when breastfeeding is continued at least nine months.

Recent studies on adults indicate obesity and insulin-resistant diabetes may be encouraged when gastrointestinal microflora does not break food down well enough to be converted to energy in the bloodstream. The absence of the harmonious balance of the microbiota is also associated withinflammatory bowel disease and other chronic conditions.

Two events in adulthood alter the balance of gut flora — antibiotic use and dramatic change in diet — and researchers, led by Tine Rask Licht of the Technical University in Denmark, wanted to know if a dramatic change in diet — the end of breastfeeding — had the same effect on young children.

The Licht team tracked the proliferation of 31 gastrointestinal strains of microbiota in 330 healthy toddlers at three stages of early childhood. Feces samples of each of the children were collected for analysis when the child was 9 months old and again at ages 18 and 36 months. Weaning time for each child was also documented.

Licht and her team of researchers discovered that the single nutrition-related factor that had the highest impact on the child's microbial composition was the end of breastfeeding, with the biggest difference occurring at 9 months. The gastrointestinal microflora of children still breastfeeding at 9 months was markedly different from those who had already been weaned.

In all the children, the period between 9 months and 18 months of age was met with swings in the enterotypes in the children's digestive tracts. An enterotype is the balance of different strains of microflora. In adults, enterotypes are relatively stable. In the children in the study, enterotypes were unstable until about age 18 months.

Between 18 and 36 months, enterotypes stabilized a bit although enterotype composition changed a few times in between. At 18 months, certain bacterial strains were more dominant than others. At 36 months, other strains had claimed the dominant position and overall enterotype was becoming similar to that of an adult.

When the gut flora of children who were still breastfeeding at age 36 weeks were compared to those no longer breastfeeding, there was still a difference but the difference was not as distinct as the difference at 9 months.

The research team suggests that their findings could lead to enhanced supplementation of baby formula so as to promote a healthy gastrointestinal microbiome.

Source: Licht, Tine Rask, et al. "Establishment of intestinal microbiota during early life: A longitudinal, explorative study of a large cohort of Danish infants (manuscript)." Applied and Environmental Microbiology. American Society for Microbiology. Feb 28, 2014. Web. Apr 1, 2014.