Background: The complementary feeding period, spanning from 6 to 24 months of age, marks the transition from an exclusive liquid diet in infants to a dietary pattern requiring the introduction of solid foods to meet nutritional demands. Complementary feeding coincides with other critical development windows, including the maturation of the gut microbiome. However, the effects of specific solid foods on gut microbiota and the subsequent influence on health outcomes require further investigation. Methods: This narrative review analyzes published research from January 2004 to October 2024 and aims to summarize the current evidence of the effects of complementary feeding on the infant gut microbiota. Results: A total of 43 studies were included in this review. Overall, multiple studies reported an increase in alpha-diversity after solid food introduction. Bifidobacteriaceae is the predominant bacterial family during the first 6 months of life, shifting to Lachnospiraceae, Ruminococcaceae, and Clostridium spp. after the introduction of solid foods. The timing of solid food introduction may also influence gut microbiota, though results were inconclusive. The effect of individual dietary components on the gut microbiota was conflicting, with limited evidence to make inferences. Conclusions: Because of variations in study design, dietary intake quantification, and minimal follow-up, a lack of conclusive evidence exists describing the relationship between complementary feeding and gut microbiota outcomes in infants. Future research to describe these relationships should focus on the impact of individual foods on microbial diversity and maturation, as well as the relationship between microbiota and infant health outcomes.

Throughout infancy, changes in growth and development are observed, including changes in nutritional requirements; at approximately 6 months of age, when complementary feeding begins, breastmilk and/or formula are no longer the sole source of energy and nutrients. Little is known about the impact of complementary feeding (CF) approaches used during this time on infant nutrition and growth. Baby-led weaning (BLW) has continued to gain popularity over the last two decades, emphasizing the importance of examining the adequacy of different CF methods. This narrative review of 19 studies from January 2010 to April 2024 aims to discuss the differences between BLW and conventional weaning (CW). The definition of BLW varied across studies, and no standard definition has been established. Though no differences in energy were reported, macronutrient and micronutrient intakes were variable between approaches, including for micronutrients such as iron and zinc. Of the few studies with growth data, results comparing BLW and CW were conflicting. Differences were seen in the demographics of parents who chose to follow BLW and breastfeeding prevalence and duration prior to complementary feeding. Additional research is needed to understand the impacts of BLW and CW on nutrient intakes and growth to inform recommendations for infant complementary feeding approaches.

Background: An urgent need exists for evidence-based dietary guidance early in life, particularly regarding protein intake. However, a significant knowledge gap exists in the effects of protein-rich foods on growth and development during early complementary feeding.Methods: This is a randomized controlled trial of infant growth and gut health (primary outcomes). We directly compare the effects of dietary patterns with common protein-rich foods (meat, dairy, plant) on infant growth trajectories and gut microbiota development (monthly assessments) during early complementary feeding in both breast- and formula-fed infants. Five-month-old infants (up to n = 300) are randomized to a meat-, dairy-, plant-based complementary diet or a reference group (standard of care) from 5 to 12 months of age, with a 24-month follow-up assessment. Infants are matched for sex, mode of delivery and mode of feeding using stratified randomization. Growth assessments include length, weight, head circumference and body composition. Gut microbiota assessments include both 16S rRNA profiling and metagenomics sequencing. The primary analyses will evaluate the longitudinal effects of the different diets on both anthropometric measures and gut microbiota. The secondary analysis will evaluate the potential associations between gut microbiota and infant growth.Discussion: Findings are expected to have significant scientific and health implications for identifying beneficial gut microbial changes and dietary patterns and for informing dietary interventions to prevent the risk of overweight and later obesity, and promote optimal health.Clinical Trial Registration:www.ClinicalTrials.gov, identifier: NCT05012930.

Introduction: Complementary feeding is a critical period marked by rapid changes in the infant’s diet, nutrient needs, and gut microbiota. However, the effects of specific foods introduced during complementary feeding, such as blueberries, on the developing infant gut microbiota remain unclear. Our primary aim was to evaluate the effect of daily consumption of freeze-dried blueberry powder during complementary feeding on gut microbiota development in U. S. human-milk-fed infants.Methods: In a double-blind, randomized, placebo-controlled feeding trial, infants from the Denver metro area (Colorado, United States) were randomly assigned to consume up to 10 g of freeze-dried blueberry powder or an isocaloric placebo powder, combined with liquid or semi-liquid and served as a puree, daily from 5 to 12 months of age. Stool samples were collected bimonthly to assess gut microbial diversity and composition. Novel taxa were identified through parsimony insertion into the SILVA reference phylogenetic tree. Infant length, weight and dietary intakes were also assessed.Results: Seventy-six caregiver-infant pairs consented and enrolled in the study and 61 completed the study (blueberry group n = 30, placebo group n = 31). There were no differences between groups in energy or macronutrient intakes from complementary foods. Growth z-scores were comparable between groups. Gut microbiota alpha diversity increased over time in both groups (effect of time p < 0.001). Several taxa, including Veillonaceae, Flavonifractor, Subdoligranulum, and Butryicicoccus (all more abundant in the blueberry group), and Actinomyces, Escherichia, Streptococcus, and Romboutsia (more abundant in the placebo group) had group-by-time interactions that trended toward significance.Conclusion: Introducing blueberries as one of the first complementary foods, in the form of freeze-dried powder served as a puree, exerts potential benefits in gut microbiota development and maturation in this cohort of human-milk-fed infants.Systematic review registration: https://clinicaltrials.gov/study/NCT05006989.

Background/Objectives: The complementary feeding period is a critical window for shaping infant diet, gut microbiota, and immune development. While allergic symptoms often emerge in the first year of life, the effects of specific foods, such fruits, on infant allergy symptoms, inflammation, immunity and associated microbiota remain unclear. This study aimed to assess the impact of daily blueberry consumption during the complementary feeding period on allergy-related symptoms, immune biomarkers, and gut microbiota in breastfed U.S. infants. Methods: In a double-blind, randomized, placebo-controlled trial, infants from the Denver metro area were assigned to receive up to 10 g/day of freeze-dried blueberry powder or an isocaloric placebo from 5 to 12 months of age. Stool, blood, and caregiver-reported allergy-related symptom data were collected at baseline and study end. Results: Of the 76 infants enrolled, 61 completed the study (Blueberry: n = 30; Placebo: n = 31). While more infants in the blueberry group had allergy-related symptoms at baseline, they had significantly different longitudinal symptom trajectories than the placebo (p = 0.05), showing a greater resolution rate of symptoms by study end. Pro-inflammatory serum IL-13 levels were significantly reduced (p = 0.035) and anti-inflammatory IL-10 levels borderline increased (p = 0.052) in the blueberry group. However, changes in allergy symptoms were not significantly associated with IL-10 or IL-13. The relative abundances of Lacticaseibacillus, Blautia, and Peptostreptococcaceae at 12 months were negatively correlated with IL-10, while Lactobacillus, Clostridiaceae, and Megasphaera were positively associated. IL-13 was positively associated with Citrobacter and negatively associated with Anaerostipes and Blautia. Conclusions: The consumptio9n of blueberries as an early complementary food may improve resolution of allergy symptoms, modulate immune biomarkers, and promote beneficial shifts in gut microbiota during infancy. Future research should aim to identify the specific bioactive components of blueberries responsible for these effects and explore the potential of other complementary foods to favorably influence developing biological systems involved in microbiota and immune development.

Early infant feeding and weight gain can impact the development of chronic diseases. 1,5 anhydroglucitol (1,5-AG) is a measure of hyperglycemic excursions (HEs) and decreases during HEs due to increased urinary excretion. We hypothesized that HEs as measured by 1,5-AG are associated with infant rapid weight gain (RWG). Infants from the Maternal and Infant Nutrition Trial, a randomized controlled feeding trial, participated in this exploratory secondary analysis. Saliva from 127 infants aged 5 mo was collected before the introduction of complementary foods. Saliva 1,5-AG concentration was measured using liquid chromatography-mass spectrometry and log transformed for statistical analyses. Demographic, anthropometric, and feeding mode [exclusively human milk-fed (EHMF), exclusively formula fed (EFF), and mixed fed (MF)] data were collected. RWG was classified as an increase in the weight-for-age z-score (WAZ) >0.67 from birth to 5 mo. Saliva 1,5-AG concentrations were negatively correlated with an increase of WAZ at 5 mo (r = -0.238, P = 0.01). EHMF and MF infants had significantly greater 1,5-AG values (-0.252 ± 0.639 and 0.332 ± 0.912, respectively) than EFF infants (-1.754 ± 0.705, P = 0.001). Birth weight, but not sex, age, or maternal body mass index, was positively associated with WAZ changes. Saliva 1,5-AG concentrations remained inversely associated with the change in WAZ values in adjusted regression models when controlling for birth weight (β: -0.214; 95% confidence interval: -0.38, -0.05), but not when mode of feeding was included. The odds ratio for 1,5-AG (0.50; 95% confidence interval: 0.28, 0.90) was also significantly associated with RWG using logistic regression controlling for birth weight. These results suggest that human milk-fed infants have fewer HEs than EFF infants. Lower saliva 1,5-AG concentrations were associated with an increase in WAZ and RWG. Additional analyses are needed to evaluate the underlying drivers of HEs and their association with infant growth and health. This study was registered at clinicaltrials.gov as NCT05012930.