Research examines whether meat or dairy-based complementary foods affect gut microbiota and growth

The impact of the intestinal microbiota on human health, including the risk of obesity, has been analyzed mainly with animal models and adults. Recent research indicates that early colonization may play a critical role in the establishment and maturation of gut microbiota. Early complementary feeding (around 5-12 months) is when infants are slowly introduced to solid foods because they are not solely dependent on infant formula or breast milk. Gut microbiota changes and growth trajectories during these periods have been reported to program body composition, long-term weight, and disease risk.

Study: Different gut microbiota in US formula-fed infants consuming meat versus dairy-based complementary foods: a randomized controlled trial. Image Credit: Lopolo/Shutterstock

A large cohort study indicated that a deviation from the normal gut microbiota in Malawian infants can lead to stunted growth. Moreover, transplantation of such gut microbiota from stunted infants to germ-free mice also altered phenotypes in mice. Two other studies also reported slower weight gain in Malawian infants and stunted growth in preterm infants associated with low gut microbiota diversity. However, it is still unclear what impact complementary foods have on the gut microbiota of infants, as most research has taken place in cohort studies and in low-resource settings.

Although diet impacts the intestinal microbiota, very few studies have analyzed the impact of solid or complementary foods on the development of the infant microbiota. For example, one study reported that a meat-based supplemental diet increased the abundance of certain commensal strains compared to a conventional iron-fortified cereal-based diet for infants 5–9 months old. However, it remains unclear whether these diet-induced changes in gut microbiota can impact infant growth.

A recent study that compared meat and dairy products as the main source of protein from complementary foods in infants aged 5 to 12 months reported an increase in length Z score for the age (LAZ) in the meat group. while an increase in the weight-for-height Z score (WLZ) parameter as well as an increased risk of overweight were 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 the association between metabolites and infant growth parameters were observed between the two groups.

A new study in the journal Nutrition Frontiers 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, exclusively formula-fed infants who were then randomized to consume a complementary dairy or meat-based diet from 5 to 12 months of age. The meat group consumed pork, beef, and poultry (provided), while the dairy group consumed cheese, yogurt, and whey protein powder (provided). Participants’ height and weight were assessed at baseline (5 months), at the monthly home visit, and at the end of the intervention (12 months). Collection of stool samples took place at 5, 10 and 12 months of age, as well as soiled disposable diapers with biodegradable liners.

Bacterial profiles were assessed by DNA extraction from stool samples, broad-spectrum amplification, and 16S rRNA gene sequence analysis. This was followed by alignment using Illumina Miseq paired reads to the hg19 human reference genome with bowtie2 and assessment of fecal short-chain fatty acids (SCFAs).

Study results

The results indicated that a total of 64 infants completed the study, of which 59 stool samples were collected at baseline, 52 at 10 months and 57 at 12 months. No differences were observed in gender, birth duration, maternal education or maternal BMI between the two groups. Mothers are on average overweight, with a BMI between 25 and 29.9. An increase in LAZ was reported in the meat group compared to the dairy group, while WAZ increased in both groups.

Differences according to age were observed in the two groups between 5 and 10 months and between 5 and 12 months. However, no significant difference was observed between 10 and 12 months. Significant differences in beta diversity were observed at 12 months between 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. In addition, a significant increase in alpha diversity was observed between 10 and 12 months. A difference in alpha diversity between the two groups was only observed at 12 months.

The four most abundant phyla at the three time points were Proteobacteria, Bacteroides, Actinobacteria, and Firmicutes. No difference in branching was observed at 5 months between the diet groups. However, it was observed that the abundance of Firmicutes increased with time while Proteobacteria and Actinobacteria decreased. Akkermansia, of the phylum Verrucomicrobia, was reported to be the only taxon with a significant group-time interaction at the genus level. An increase in the 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 in all infants after adjusting for diet group. Four of the five differentially abundant taxa of the phylum Proteobacteria have been observed to decrease in abundance with age. Additionally, 10 out of 11 Firmicutes taxa increased with age. In addition, a significant factor change in 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 indicator of alpha diversity, 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 gut microbiota diversity and community restrictions, impacting infant growth. More research is needed to understand if these effects have long-term impacts.

Boundaries

The study has certain limitations. First, the sample size of the study was small. Second, collection of microbiota samples was infrequent. Third, the study included only formula-fed infants, but no breastfeeding comparison group. Fourth, the different protein quality between meat and dairy products may lead to different dietary protein availabilities as well as different amino acid compositions, which could have a different impact on the structure of the gut microbiota.