Transition to Infant Formula Feeding on Gastrointestinal Regurgitation (TIGER) Study

Inclusion Criteria: * healthy full-term born infants (≥ 37 weeks + 0 days and \< 41 weeks + 6 days of gestation) * birth weight ≥ 2.5 kg and ≤ 4.5 kg * born from a singleton pregnancy * live in Bangkok or nearby with no plan for geographical migration before 6 months of age * for experimental and active comparator groups only: parent(s) has expressed the intention to partially (in combination with breastfeeding) or fully formula-feed the infant and ready to enroll in the study before the age of 4 months/120 days * for no intervention group only: parent(s) has expressed the intention to predominantly breastfeed (according to study definition) and ready to enroll in the study before the age of 4 months/120 days * infant has been predominantly breastfed for at least 2 weeks before enrollment * parent(s) has sufficient Thai language skills to understand the study information, the informed consent, and to comply with the study procedure * parent(s) is willing and deemed able to fulfil the requirements of the study protocol and procedures * at least one parent is of legal age of consent Exclusion Criteria: * infant has any disorder considered to interfere with nutrition, growth or development of the immune system * participation of the infant in any other interventional trial or participation of the mother in any intervention trial with infant follow-up * for experimental and active comparator groups only: infant has been formula-fed for more than 1 week before enrolment * for e…