Immunonutrition in Early Life: The Role of Complementary Feeding, Dietary Patterns, and Nutritional Exposures on the Health of Young Children—An EAACI Scoping Review

BACKGROUND: Immunonutrition examines how diet influences immune development. Complementary feeding represents a critical window for long-term health. We aimed to map evidence linking complementary feeding to immune outcomes, allergy, infection, and growth in infants and toddlers (≤ 3 years). We conducted a scoping review and evidence-gap mapping, following PRISMA-ScR. MEDLINE and Epistemonikos were searched from inception to November 2024. Concepts included diet diversity/patterns, feeding practices/models, and timing of allergen introduction, timing of complementary feeding, macronutrients, micronutrients, foods, supplementation, and ultra-processed foods. We included systematic reviews and recent primary studies meeting criteria. RESULTS: From 13,512 records screened, 108 systematic reviews were included, comprising 99 randomized controlled trials, 41 cohorts, 22 case-control, and 14 cross-sectional studies. Most reviews addressed nutrient intake, supplementation, or timing of allergen introduction, while fewer reviews explored diet diversity, foods, or ultra-processed food intake. Responsive complementary feeding was consistently associated with healthier growth and lower obesity risk, whereas restrictive practices showed adverse effects. Greater diet diversity was linked to reduced asthma and food allergy risk, though eczema findings were inconsistent. Western-style diets high in processed foods, fat, sugar, and meat correlated with higher allergy risk, while home-prepared diets were protective. Micronutrient supplementation (iron, zinc, vitamin D) reduced infection and anemia risk but had mixed effects on allergy. Early allergen introduction reduced food allergy incidence. CONCLUSIONS: Complementary feeding research now extends beyond calorie counting, macronutrients, and early allergen introduction to dietary patterns and early life nutrition that supports the microbiome. Evidence supports dietary diversity, timely food allergen introduction, and responsive feeding, while discouraging restrictive practices and ultra-processed foods. Future work should harmonize definitions and investigate plant-based diets, advanced glycation end products, and processed food exposures.