Although an ill patient is exempt from fasting on Tisha B’Av, the Mishna Berura (550:5) writes that the patient must eat and drink only as needed to sustain his or her health, and should not indulge in food and drink beyond what is necessary.
Rav Yitzchak Zilberstein (Chashukei Chemed, Yoma 73b) addresses the interesting situation of a frail patient who needs to eat on Tisha B’Av, but who could minimize his food consumption by eating meat. Meaning, if he eats meat, a small quantity would suffice to give him strength, but if he eats other foods, such as bread, he would require a larger amount. As Halakha forbids eating meat from the Motza’ei Shabbat before Tisha B’Av (or, according to Ashkenazic custom, from the beginning of Av) until midday on the 10th of Av, should this patient refrain from meat, and eat other foods to sustain his health? Or, does the interest in minimizing his consumption on Tisha B’Av override the prohibition against eating meat?
Rav Zilberstein begins by citing the theory advanced by Rav Velvele Soloveitchik (Chiddushei Ha-Griz, Hilkhot Ta’aniyot) that technically speaking, the prohibition against eating meat applies only to the se’uda mafseket – the final meal before Tisha B’Av. Although we customarily extend the prohibition to the week before Tisha B’Av, and until the day after Tisha B’Av, the technical halakhic prohibition pertains only to the meal eaten right before the fast. At this meal, Rav Velvele explained, we all have the status of an onein – a person whose family member has died but has yet to be buried – who is forbidden from eating meat, and this is when partaking of meat is strictly forbidden. According to this theory, it seems clear that in our case, eating a smaller quantity of meat is preferable to eating a larger quantity of other foods, as there is no technical halakhic prohibition against eating meat during this period (except, of course, by virtue of the requirement to fast, which is waived in the case of an ill patient).
However, Rav Zilberstein then proceeds to cite his father-in-law, Rav Yosef Shalom Elyashiv (Kovetz Teshuvot, 57), as claiming that Tisha B’Av itself is no different in this regard than the se’uda mafseket. In Rav Elyashiv’s view, partaking of meat is strictly forbidden on Tisha B’Av both by virtue of the fast, and also by virtue of the prohibition against eating meat in a state of aninut – before one’s deceased family member has been buried – the condition in which we are all in on this day of mourning. Accordingly, Rav Zilberstein cites his brother-in-law, Rav Chaim Kanievsky, as claiming that it would be preferable to eat a larger quantity of other foods in order to avoid the prohibition of eating meat on Tisha B’Av.
Rav Zilberstein then proceeds to note that this ruling may not apply in a case where the patient has the option of eating meat in a quantity smaller than the minimum quantity one needs to consume to violate the Tisha B’Av fast. The Chafetz Chayim, in Bei’ur Halakha (554:6), writes that like on Yom Kippur, one violates the Tisha B’Av fast by partaking of a kotevet (the size of a large date). The question then becomes, if a patient can sustain his strength on Tisha B’Av by eating less than a kotevet of meat, or a kotevet or more of other foods, which should he eat? It would seem, Rav Zilberstein writes, that in this case eating meat would be the preferable option, as one thereby does not technically break the fast. Since in this case the patient has the possibility of avoiding violating the fast, this would certain appear preferable to breaking the fast in order to avoid eating meat.