Exclusive breast milk is recommended from birth to 6 months of life to promote the development of a balanced intestinal microbiota. Human milk provides several bioactive components, from natural probiotics such as Bifidobacterium spp. and Lactobacillus spp., to their metabolites which colonize the intestine of the newborn. However, if breast milk is not available or insufficient, it is used formula milk as a substitute. Infant formula can be supplemented with postbiotics to promote maturation of immune, metabolic and microbial components, similar to breast milk. Postbiotics are preparations composed of both microbial constituents and their metabolites, produced during fermentation.

A balanced nutrition starting from early childhood significantly influences growth and psychomotor development. Exclusive breast milk is the recommended nutritional choice from birth to 6 months of life, as it guarantees everything necessary for growth, maturation, protection from infections, promoting the development of a balanced intestinal microbiota. Several prenatal and perinatal factors including the type of delivery, the use of antibiotics, diet and other environmental factors, can influence the microbial colonization of the newborn. Thus, it is generally accepted that the gut microbiota of the healthy, full-term, vaginally born, breastfed infant is the gold standard for a favorable microbial composition in the early years of life. Human milk provides several bioactive components, from natural probiotics such as Bifidobacterium spp. and Lactobacillus spp., to their metabolites ("natural postbiotics"), which colonize the intestine of the newborn. These metabolites regulate the development of the immune system and attenuate the inflammatory processes. However, if breast milk is not available or insufficient to meet the nutritional needs of the infant, formula milk is proposed and used as a substitute. Given the benefits, it is essential that infant formula is as close to human milk as possible, providing bioactive substances that target gut and immune system health. Current research focuses on optimizing artificial formulas, with the aim of resembling human milk in composition and functionality, with some on the market already including probiotics, prebiotics, synbiotics and postbiotics. However, it still remains to be clarified which is the best formulation and the exact consequences on the immune, metabolic and microbial system of the newborn. In particular, postbiotics are preparations composed of both microbial constituents and their metabolites, produced during fermentation. It has already been highlighted in the literature that the enrichment of formula milk with post-biotics would seem to offer advantages for feeding term infants. Furthermore, it promotes an immune, metabolic and microbial component maturation, similarly to human milk, thus making postbiotic supplements very promising and interesting in the nutrition of newborns and infants.

Inclusion Criteria:

• Weight appropriate to gestational age (percentiles >10th and <90th)
• Written informed consent

Exclusion Criteria:

• Cardiological diseases
• Liver disease
• Gastrointestinal diseases with malabsorption
• Endocrinological diseases
• Perinatal infections
• Metabolic and genetic diseases
• Born to mothers with endocrinological and metabolic diseases
• Withdrawal of informed consent

Infants born at Ospedale Buon Consiglio Fatebenefratelli, Naples