The impact of gut microbiota on human health, including the risk of obesity, has been analyzed primarily with animal models and adults. Recent research indicates that early in-life colonization can play an essential role in the establishment and maturation of gut microbiota. Early complementary feeding ( around 5–12 months of age) is when solid foods are slowly introduced to infants since they do not solely rely on infant formula or breast milk. Shifts and growth trajectories in gut microbiota during such periods have been reported to program body composition, long-term weight, and disease risks.
Study: Different gut microbiota in U.S. formula-fed infants consuming a meat vs. dairy-based complementary foods: A randomized controlled trial. Image Credit: Lopolo / Shutterstock
One large cohort study indicated that deviation from the normal gut microbiota in Malawian infants can result in growth impairment. Moreover, transplantation of such gut microbiota from stunted infants to germ-free mice also impaired phenotypes in mice. Two more studies have also reported slower weight gain in Malawian infants and growth failure in preterm infants associated with low diversity of gut microbiota. However, it is still unclear how complementary foods impact the gut microbiota of infants since most of the research has taken place in cohort studies and low-resource settings.
Although diet impacts the gut microbiota, very few studies have analyzed the impact of solid or complementary foods on the development of infant microbiota. For example, one study reported that a meat-based complementary diet increased the abundance of certain commensal strains compared to a conventional iron-fortified infant cereal-based diet from 5 to 9 months of age. However, whether such diet-induced gut microbiota changes can impact infant growth is still unknown.
A recent study that carried out a comparison of meat and dairy as the primary source of protein from complementary foods in infants between 5 to 12 months of age reported an increase in the length-for-age Z score (LAZ) increase in the meat group while an increase of the parameter weight for-length Z score (WLZ) along with an increased risk of overweight was observed in the dairy group. Increases in circulating insulin, IGFBP3, and IGF-1 were observed from 6 to 12 months, but no difference was observed between the two groups at 12 or 24 months. Additionally, no differences in biomarkers or association between metabolites and infant growth parameters were observed between the two groups.
A new study in the journal Frontiers in Nutrition aimed to analyze the impact of complementary foods on the development of infant gut microbiota and whether it is associated with infant growth.
About the study
The study recruited full-term, healthy, and exclusively formula-fed infants who were then randomized to consume a dairy or meat-based complementary diet from 5 to 12 months of life. The meat group consumed pork, beef, and poultry (provided), while the dairy group consumed cheese, yogurt, and whey protein powder (provided). The length and weight of the participants were assessed at baseline (5 months), at the monthly home visit, and end of the intervention (12 months). Collection of stool samples took place at 5, 10, and 12 months of age, along with soiled disposable diapers fitted with biodegradable liners.
Bacterial profiles were assessed through DNA extraction from the stool samples, broad-range amplification, and sequence analysis of 16S rRNA genes. This was followed by alignment using Illumina Miseq paired-end reads to human reference genome hg19 with bowtie2 and assessment of fecal short-chain fatty acids (SCFAs).
The results indicated that a total of 64 infants completed the study out of which 59 stool samples were collected at baseline, 52 at 10 months, and 57 at 12 months. No differences were observed regarding sex, birth length, maternal education, or maternal BMI between the two groups. Mothers were reported to be overweight on an average, with BMI between 25 and 29.9. An increase in LAZ was reported in the meat group compared to the dairy group, while WAZ was reported to increase in both groups.
Age-dependant differences were observed in both groups between 5 and 10 months and between 5 and 12 months. However, no significant differences were observed between 10 and 12 months. Significant differences in beta diversity were observed at 12 months between the meat and dairy groups. A significant increase in alpha diversity was reported in a comparison of 5 vs. 10 months and 5 vs. 12 months. Moreover, a significant increase in alpha diversity was observed between 10 and 12 months. A difference in alpha diversity between the two groups was observed only at 12 months.
The four most abundant phyla at all three-time points were reported to be Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes. No differences in phyla were observed at 5 months between the diet groups. However, the abundances of Firmicutes were observed to increase with time while Proteobacteria and Actinobacteria decreased. Akkermansia, of the phylum Verrucomicrobia, was reported to be the only taxon with a significant group-by-time interaction at the genus level. An increase in abundance of this genus was observed with age in the dairy group, while a decrease was observed in the meat group.
Seventeen taxa were reported that were associated with age among all infants after adjusting for the diet group. Four of the five differentially abundant taxa of the phylum Proteobacteria were observed to decrease in abundance with age. Additionally, 10 out of 11 Firmicutes taxa were observed to increase with age. Moreover, a significant fold change of butyric acid was observed in the meat group from 5 to 12 months, while no change was observed in the dairy group. Finally, Chao1, which is an alpha diversity indicator, was observed to be negatively associated with WLZ and WAZ.
Therefore, the current study demonstrated that complementary feeding is a critical developmental phase for infant growth and gut microbiota maturation. Complementary food choices can impact the diversity and community strictures of gut microbiota, impacting infant growth. Further research is required to understand whether such effects have long-term impacts.
The study has certain limitations. First, the sample size of the study was small. Second, the collection of microbiota samples was infrequent. Third, the study included only formula-fed infants but no breastfeeding reference group. Fourth, different protein quality between meat and dairy can result in differing availabilities of dietary proteins as well as different amino acid compositions, which might impact the gut microbiota structure differently.