Doctors are finding not all breast milk is the same.
There's growing evidence, the gender of the baby affects the quality of the milk.
Studies done in Massachusetts and Kenya show mothers produce milk with more fats and nutrients for boys than for girls.
In Kenya, there were also economic differences - in richer families, mothers of sons had more nutrients in breast milk.
For poorer families, that was found in mothers with daughters.
Another study is also looking at how these differences affect growth.
Experts say it's a whole new perspective on the impact of breastfeeding.
Studies reveal new links between gender, breast milk
HEALTH & FITNESS
More Health & Fitness