Breastfed babies cry more, laugh less, and generally have "more challenging temperaments" than formula-fed infants, a study has found.
But such behaviour is normal, and mothers should learn to cope with it rather than reach for the bottle, said researchers.
Bottle-feeding was akin to "comfort eating" -- producing quieter and apparently more content babies who may be over-nourished and putting on weight too rapidly.
The study rated the temperament of 316 babies at age three months using a 191-item behaviour questionnaire completed by their mothers.
Study leader Dr Ken Ong, from the Medical Research Council Epidemiology Unit in Cambridge, England, urged breastfeeding mothers to persevere despite the difficulties -- and seek help if they need it.
"There is an overwhelming body of evidence supporting breastfeeding as the normal and most healthy form of infant nutrition, and our findings do not contradict this," he said.