Immunonutrition: Feeding the gut, skin, and immune system

Background: Early life is a critical period for the maturation of the gut microbiota, epithelial barriers, and immune system. Disruption of gut and skin barrier integrity during this window is increasingly recognized as a key mechanism contributing to the development of allergic diseases. Objective: This review summarizes evidence on how infant dietary patterns and macronutrients influence epithelial barriers, microbiota development, and immune programming for allergy prevention. Methods: A comprehensive search and analysis of current literature regarding macronutrients, including carbohydrates and fiber, proteins, and fats, dietary diversity, and Western-type dietary patterns, was conducted to explore their collective effects on epithelial barrier function, microbiota, and immune outcomes during pregnancy and early life. Particular attention was given to complementary feeding. Results: Dietary composition significantly influences epithelial barrier integrity and immune development through direct nutritional effects and microbiota-mediated pathways. Dietary fibers and human milk oligosaccharides promote short-chain fatty acid production and microbial diversity, strengthening epithelial junctions, mucus secretion, and regulatory immune responses. Adequate protein intake supports epithelial renewal, while microbial metabolism of amino acids such as tryptophan and branched-chain fatty acids enhances barrier integrity and immune homeostasis. Dietary fats critically shape epithelial lipid composition, with balanced omega-3 and omega-6 fatty acids supporting barrier resilience, whereas excess saturated and trans fats promote dysbiosis and inflammation. Furthermore, greater dietary diversity during pregnancy and infancy correlates with enhanced microbial maturation and reduced atopic risk. Conversely, Western-type diets rich in ultra-processed foods and additives disrupt epithelial barriers and promote pro-inflammatory immune programming with long-lasting consequences beyond infancy. Conclusions: Optimizing maternal and early life nutrition through breastfeeding support, timely and diverse complementary feeding, adequate intake of fiber, high-quality proteins and fats, and avoidance of Western-type dietary patterns represents a promising strategy to support gut and skin barrier and to reduce the risk of allergic diseases across the lifespan.