Causes of possible excessive weight gain in exclusively breastfed infants in the first six months of life.

Background: The aim of this study was to describe factors related to the infant, mother, and breastmilk composition that may be associated with excessive weight gain in a cohort of exclusively breastfed infants younger than 6 months of life with excessive weight gain, and to compare these findings with data from a group of normal-weight exclusively breastfed infants.

Methods: Thirty-six exclusively breastfed infants younger than 6 months of life seen at two health-care centers between July 2016 and 2017 were enrolled in the study. The clinical features of the infants, their mothers, and the macronutrient composition of the breast milk were evaluated. We classified infants according to weight gain velocity between birth and 6 months of life into an excessive weight gain (EWG) and an adequate weight gain (AWG) group.

Results: Mean age at protocol entry was 3.8 months. Thirteen patients were classified as EWG and 23 patients as AWG. Co-sleeping was more often observed in EWG than in AWG infants. Mothers in the EWG group were younger and more often had gained more than 18 kg during pregnancy than those in the AWG group. No significant differences were found in the macronutrient content of the breast milk between both groups.

Conclusions: Greater weight gain in infants under 6 months of age may be related to greater weight gain of the mother during pregnancy, younger age of the mother, and co-sleeping of the mother and child.