A randomized double blinded controlled study including infants at the age of 1 month . Infants are assigned randomly to either infant formula supplemented with B. breve CECT7263 or L.fermentum CECT5716 (Probiotic groups), or the same formula without the probiotic strain (Control group). The primary outcome of the study is the body weight gain of infants. Secondary outcomes are incidence of infections, symptoms related with intestinal function, and fecal microbiota