[2] Some Aĥaronim maintain that, le-khatĥila, even on Tisha Be-Av a sick person should preferably eat quantities of less than a shi’ur, so that he does not technically break his fast and can thus recite the Aneinu and Naĥem additions to the prayer (cited in Sdei Ĥemed and in Tzitz Eliezer 10:25, 16:2). bhl 554:6 rules similarly, quoting Pitĥei Olam as saying that in a place where cholera is not already rampant and the doctors say that people must eat in order to avoid catching the disease, one should eat portions that are smaller than the shi’ur on Tisha Be-Av. Similarly, mb 554:14 states in the name of Eliya Rabba that a postpartum woman should preferably fast for a few hours, if possible. Ĥatam Sofer oĥ 157 concurs, saying that if a sick person can suffice with just drinking, he should not eat, and if eating once will satisfy his needs, he should not eat twice. According to Maharil Diskin (Kuntres Aĥaron §75), there is room to be stringent in this matter, not as far as the obligation to fast is concerned, but in order to avoid separating from the community.

In practice, if a sick person wants to be stringent and eat portions that are smaller than the shi’ur, he may later recite Aneinu and Naĥem, and some indeed go above and beyond in following this practice. Although the general rule is that sick people do not need to eat portions that are smaller than the shi’ur. So states ahs 554:7. Furthermore, even bhl only ruled that one should eat less than the shi’ur in reference to one who is not considered sick at all. Nishmat Avraham 4:554 and Tzitz Eliezer 10:25:16 concur.

Sometimes it is not certain whether a person is sick or not. It seems that if the uncertainty stems from the person’s weakness – i.e., that it is likely that he will become truly sick over the course of the fast, as in the case of a pregnant woman who feels weak – it is proper to instruct him to begin eating and drinking less than the shi’ur in the morning, in accordance with the ruling of bhl. If, however, the uncertainty stems from the person’s fear, there are grounds to instruct him to begin fasting, but to eat and drink if his illness intensifies.

[3] Rema 554:6 writes that a woman should fast if seven days have passed since childbirth, unless she is in great pain. mb ad loc. 14 quotes ma as saying that she may be lenient only if Tisha Be-Av is postponed. Nevertheless, ahs 554:7 states that nowadays a woman should not, God forbid, fast within thirty days of giving birth. Other Ashkenazic poskim rule this way as well. A woman who is lenient in this regard does not lose out at all.

[4] Many Ashkenazic poskim maintain that one recites Naĥem before the ending of the berakha of U-venei Yerushalayim (Rema 557:1). Others questioned this, claiming that the Sages never instituted the recitation of Naĥem in Birkat Ha-mazon (Vilna Gaon, quoted in mb 557:5). Still others say that it is best to recite it after all the berakhot of Birkat Ha-mazon are finished, together with the Ha-raĥaman prayers (Kaf Ha-ĥayim 557:11).