Four fasts were decreed by the sages to commemorate critical events in the destruction of the First and Second Temples and the dispersion of Jews into exile. Nursing women are exempt from fasting on three of these fasts: Tzom Gedaliah, the Tenth of Tevet, and the 17th of Tammuz. (They are also exempt from Ta'anit Esther.) There is a difference of opinion as to whether a nursing woman who feels well should try to fast even though she is not required to. The Rema seems to indicate that the custom is to fast if it is not too difficult for her. However, the Mishneh Brurah states that a nursing woman who feels any weakness should not fast.
On Tisha B'Av, the anniversary of the actual destruction of both Temples, the halacha requires nursing women to fast the entire day. Unlike the other fasts, which last from dawn to dusk, the fast of Tisha B'Av is a little over 24 hours long.
There has been little study of the effect of fasting on breastfeeding. The only published article to date showed minimal biochemical changes in the milk and a small reversible decrease in milk supply on the day following a 24-hour fast. Thus, healthy women who are easily nursing healthy babies should fast the entire day.
In the first week after childbirth, there is more room for leniency. For the first three days after childbirth, a woman is considered a cholah sheyesh bah sakanah, an ill person in danger, and should not fast at all. For the next four days, if she feels that she should not fast, she does not need to fast. There is some room for leniency on Tisha B'Av for the first 30 days after childbirth as well.
These are general guidelines. Halacha and medicine are both case based. If a woman has some complication of childbirth, if the baby is even mildly ill, or if she is having difficulty breastfeeding, she should consult with her physician about his or her concerns with not drinking or eating for 24 hours and relay these concerns to her rabbi. It is important that the physician be sensitive to the seriousness of this fast and give a well thought out answer.
The fast of Yom Kippur is Torah obligation (Vayikra 16:29 and 23:27). Therefore, the rules of this fast are the strictest of any fast during the year. The halacha assumes that nursing women will fast on Yom Kippur.
For most healthy women, based on the limited medical information available, this practice is unlikely to permanently affect breastfeeding. Thus healthy women nursing healthy babies without problems must fast. If the woman is not feeling well, or the nursing has not been going well, a specific halachic question should be asked.
In the first week after childbirth, there is much more room for leniency. For the first three days after childbirth, a woman is a cholah sheyesh bah sakanah (an ill person who is at risk), and is not allowed to fast. For the next four days, she may only fast if she both feels up to it and her health care provider does not object. The exact calculation of these time periods is a matter of halachic debate (whether 24-hour days, or nightfall to nightfall). Therefore, in borderline situations, a specific halachic question should be asked.
Shiurim (Minimum Quantities)
The prohibition against eating or drinking on Yom Kippur extends even to tiny amounts. However, the penalty for violating this prohibition applies only if a certain quantity (shiur) of food or drink is consumed. Therefore, one for whom fasting is dangerous may sometimes be instructed to eat or drink less than a shiur at one time.
The shiur for drinking is half of one mouthful (measured before the fast by filling the mouth and cheeks with liquid, emptying it into a measuring cup, and halving that). If eating is necessary, a woman may eat up to 30cc at a time. Ideally, these quantities should be consumed at intervals of at least nine minutes; however, opinions vary and some authorities permit intervals as short as four minutes. A woman who needs to break her fast should have in mind while eating that she is fulfilling the mitzvah of "vechai bahem", living for the sake of Torah (and not risking life).
These are general guidelines. Halacha as well as medicine is case based. If a woman has some complication of childbirth, the baby is even mildly ill, or she is having difficulty breastfeeding, she should consult with her physician about his or her concerns with not drinking or eating for 24 hours and relay these concerns to her rabbi. It is important that the physician be sensitive to the seriousness of this fast and give a well thought out answer.
Practical tips for fasting and breastfeeding include:
- Drink plenty of fluids for a number of days before the fast.
- Consider pumping some milk a day or two before, so that you have some expressed milk to offer the baby if you are tired at the end of the fast and feel you are producing less milk.
- After the fast, breastfeed frequently, drink and rest. Your milk supply should return to normal within 1-2 days.
- Do not start giving formula at this stage. This will give your body the message that less milk is necessary, and is likely to diminish your supply. If you are concerned the baby is not getting enough, give your pumped milk.
- A baby who produces wet and dirty diapers is well nourished.
- It is more important to stay home and fast and breastfeed than to break your fast and attend synagogue. It is also more important for you to fast than for your husband to attend synagogue.
- Discussion should take place prior to the fast about family arrangements (e.g., husband staying home a few hours, hiring a babysitter) that can help make it easier.