Complementary Feeding in Developed Countries: The 3 Ws (When, What, and Why?).

While a wide knowledge exists on the effects of breast milk or infant formula on growth and infant development, less attention has been paid to the importance of complementary feeding (CF). This review focuses on current recommendations for optimal introduction of CF in healthy full-term European infants and discusses the potential impact of this type of feeding on health outcomes. Overall, exclusive breastfeeding is recommended at least for 4 months and preferable for 6 months, followed by the introduction of CF alongside breast milk; infants' nutrient requirements must meet the differences between nutrients provided by breast milk and the estimated total needs. There is growing evidence that healthy feeding practices during the CF period have positive short- and long-term effects on optimal growth, body composition, neurodevelopment, healthy food preferences, and gut microbiota composition and function; adequate and healthy CF may also diminish the risk of infections, allergies, type 1 diabetes mellitus, as well as celiac and non-communicable diseases. Following the expert recommendations, the design of nutritional strategies must encourage parents to provide a healthy lifestyle for their offspring. Future research should aim to optimize timing, content, and methods of CF; furthermore, it is necessary to explore future CF-targeted health-promoting strategies in early life (appetite regulation, eating patterns, eating behavior, gut dysbiosis, etc.) to prevent growth/obesity outcomes, immune system related-diseases or non-communicable diseases in later life.