During and after birth, the body of a healthy infant is rapidly colonized by microorganisms and several factors can shape microbial colonization. The most studied ones include delivery method, antibiotics, and diet. Establishment of an adult-like microbiome is estimated to occur within the first 3 years of life, and the infant gut microbiome may play an important role in the development of some non-communicable diseases in later years. The effects of ethnicity on the gut microbiome in early life has not been fully explored.

A recent study, led by Dr. Jennifer C. Stearns from McMaster Univeristy in Hamilton (Canada), has found that ethnicity and infant feeding practices independently influence the infant gut microbiome at 1 year.

The researchers collected stool samples at 1 year of age from 173 white Caucasian and 182 South Asian healthy infants from two prospective Canadian birth cohorts (the Canadian Healthy Infant Longitudinal Development study, or CHILD Study, and the South Asian Birth Cohort, or START-Canada). The main objective was to investigate whether ethnicity (referring to certain racial, cultural, religious, or other traits that groups of people have in common) and breastfeeding affected the infant gut microbiome, while accounting for several variables that represent dietary differences as well as other exposures throughout infancy, including maternal antibiotic use, gestational diabetes, vegetarianism, infant milk diet, time of introduction of solid food, infant birth weight, and weight gain in the first year.

Abundance of microorganisms within all samples were found to be significantly affected by ethnicity after taking into account breastfeeding at time of collection. And although previous research in adults has shown that the host’s geographic location may impact the gut microbiome, the effect of ethnicity was larger than the effect of geographic location, as samples from South Asians were separated from white Caucasians from all study centres in the principal coordinate analysis. The strong effect of ethnicity persisted after stratifying samples by currently breastfed and not currently breastfed infants.

Breastfeeding status at the time of sampling, infant age at time of stool collection, and weight gain in the first year of life were the only significant predictors of the gut microbiome differences by ethnicity, according to the authors. After taking into account these variables, lactic acid bacteria, specifically Bifidobacterium, Lactococcus, Streptococcus, and Enterococcus, were more abundant within South Asians while several genera within the order Clostridales were higher in abundance in white Caucasians. Both the orders Lactobacillales and Clostridales are phylogenetically distinct, which suggests that the gut microbiomes of South Asian and white Caucasian infants exhibit different metabolic pathways that may be responding to their heterogeneous diets.

In conclusion, both ethnicity and breastfeeding are key determinants of the gut microbiome composition in the first year of life. After accounting for potential confounds, breastfeeding, infant age, and weight gain in the first year of life were shown to significantly influence the infant gut microbiome. Prospective follow-up studies are needed in order to clarify whether the effect of ethnicity on the gut microbiome may affect long-term health outcomes.




Stearns JC, Zulyniak MA, de Souza RJ, et al. Ethnic and diet-related differences in the healthy infant microbiome. Genome Med. 2017; 9(1):32. doi: 10.1186/s13073-017-0421-5.