Inclusion Criteria related to mother:  Residing in Aarhus area Above 18 years of age BMI above 18.5 kg/m2 Intention to breastfeed the first four to six months following birth Be able to communicate in Danish  Exclusion Criteria related to mother:  Smoking Multiple gestation Suffering from the following chronic diseases that demands medical treatment: diabetes mellitus, celiac disease, inflammatory bowel disease (Chrohn's disease or ulcerosa colitis) Taking medicaments for irritable bowel syndrome Taking medicine for metabolic disorders Taking medicine for psychological disorders Have had gastric bypass surgery Planned caesarean section Received antibiotics after week 12 in their pregnancy Utilizing significant amount of infant formula following birth  Inclusion Criteria related to infant:  Infants born after gestational age 37 weeks Infants with a birth weight between 2500 g and 5000 g  Exclusion Criteria related to infant:  • Inborn errors of metabolism