The WHO recommends that complementary feeding (weaning) should begin between four- to six-months-old. It is important that weaning progresses during this window in order to optimise growth and the development of the digestive system.17
The introduction of solid food causes a change in the gut microbiome. The infant’s microbial composition transitions from an abundance of Bifidobacteria to Bacteroidetes and Firmicutes dominant communities.16 By three-years-old, a child’s microbiome composition resembles that of an adult.18
The gut microbiomes of children (three- to ten-years-old), compared with those of infants are much less dynamic. Geographical location and cultural dietary differences are prime factors that alter the microbiota in childhood. Children living in economically developed countries have been found to have poor microbial diversity and a dominance of microbes which are associated with high animal protein and high-fat diets (i.e. Bacteroides and Firmicutes).16
Children living in less economically developed countries have been found to have higher microbial diversity and a dominance of microbes associated with carbohydrate-rich diets (i.e. Prevotella). These differences in microbial composition may coincide with increased incidence of autoimmune diseases such as Inflammatory Bowel Disease (IBD) in developed countries,16 however further research is required.