It is well established that a breast-feeding women need more protein in their diet compared to non-lactating women, but how much additional protein is needed remains unclear. There is reason to believe that the current Dietary Reference Intake (DRI) recommendations for breast-feeding women are too low. To gain better understanding, we plan to study healthy breast-feeding women 20 - 45 yrs, between 3 - 5 months lactation and 6 - 8 months lactation. We will use the indicator amino acid oxidation technique (IAAO), which is a modern, quick and safe research method.