The Effect of Breast-Feeding with and without Formula Use on the Risk of Obesity at 4 Years of Age.

While there have been many studies examining whether breastfeeding is associated with a reduced risk of childhood obesity, it has not been clear how long mothers need to breastfeed to reduce their child’s risk of obesity, and whether the use of formula in conjunction with breastfeeding lessens its protective effect. In this study of 73,000 low-income children, researchers found that for breastfeeding to reduce the risk of obesity in preschool children, mothers must breastfeed for at least four months without using formula or for at least six months if they are also formula feeding. Breastfeeding, of any duration, was not found to be protective against obesity among black children or among children whose mothers smoked during pregnancy.