Fasting for a Nursing Mother Who Is Weak
Question
Greetings, Rabbi! My wife is six weeks postpartum and still feels weak. In addition, she is breastfeeding fully. Does she need to fast? I should mention that she says she has no idea how she will manage to fast, especially because of the full breastfeeding. Thank you.
Answer
Shalom!
If she is extremely weak, to the point where she needs to lie in bed, she should not fast.
If she is somewhat weak, and has not yet regained her strength, she should try to fast, prepare well by drinking a lot beforehand, and avoid exertion.
If she starts to feel significantly weaker during the fast, or if it is observed that there is a lack of milk for the baby, she should start drinking immediately.
Source
Shulchan Aruch, section Orach Chaim, chapter 554, paragraph 6.