A number of studies have shown that breastfed babies grow slightly slower and are slightly slimmer than children who are fed with infant formula. Children who are breastfed also have a slightly lower incidence of obesity, allergies, diabetes and inflammatory bowel disease later in life. According to a new study by the National Food Institute and the University of Copenhagen this may be due to the fact that breastfeeding promotes the development of beneficial bacteria in the baby’s gut. “We have become increasingly aware of how crucially important a healthy gut microbial population is for a well-functioning immune system. Babies are born without bacteria in the gut, and so it is interesting to identify the influence dietary factors have on gut microbiota development in children’s first three years of life,” research manager at the National Food Institute Tine Rask Licht says. “The results from the study can be used to support initiatives that can be used to help children develop a type of gut microbiota, which is beneficial for the immune system and for the digestive system .”
Gut microbes change in the first years of life
The study shows that there are significant changes in the intestinal bacterial composition from nine to 18 months following cessation of breastfeeding and other types of food being introduced. However, a child’s gut microbiota continues to evolve right up to the age of three, as it becomes increasingly complex and also more stable.
“The results help to support the assumption that the gut microbiota is not – as previously thought – stable from the moment a child is a year old. According to our study important changes continue to occur right up to the age of three. This probably means that there is a ‘window’ during those early years, in which intestinal bacteria are more susceptible to external factors than what is seen in adults,” Tine Rask Licht explains.
Study Methods
Fecal samples were obtained from a cohort of 330 healthy Danish infants at 9, 18, and 36 months after birth, enabling characterization of 
interbacterial relationships by use of quantitative PCR targeting 31 selected bacterial 16S rRNA gene targets representing different phylogenetic levels. Nutritional parameters and measures of growth and body composition were determined and investigated in relation to the observed development in microbiota composition. The study found that significant changes in the gut microbiota occurred, particularly from age 9 to 18 months, when cessation of breastfeeding and introduction of a complementary feeding induce replacement of a microbiota characterized by lactobacilli, bifidobacteria, and Enterobacteriaceae with a microbiota dominated by Clostridium spp. and Bacteroides spp.
Classification of samples by a proxy enterotype based on the relative levels of Bacteroides spp. and Prevotella spp. showed that enterotype establishment occurs between 9 and 36 months. Thirty percent of the individuals shifted enterotype between 18 and 36 months. The composition of the microbiota was most pronouncedly influenced by the time of cessation of breastfeeding. From 9 to 18 months, a positive correlation was observed between the increase in body mass index and the increase of the short-chain-fatty-acid-producing clostridia, the Clostridum leptum group, and Eubacterium hallii. Considering previously established positive associations between rapid infant weight gain, early breastfeeding discontinuation, and later-life obesity, the corresponding microbial findings seen here warrant attention.
“The results from the study can be used to support initiatives that can be used to help children develop a type of gut microbiota, which is beneficial for the immune system and for the digestive system . This could for example be advice to mothers about breastfeeding or the development of new types of infant formula to promote the establishment of beneficial bacteria in the gut,” Tine Rask Licht says.
This is the first time researchers have used newer, culture-independent methods based on ‘signature sequences’ in the bacteria’s DNA to investigate changes in the gut microbiotia in such a large group of children over such a long period of time.
