This is the rule decided upon by the head of the Petach Tikva Hesder Yeshiva Rabbi Yuval Sherlow, right before Tisha B'Av.
The rabbi explained that “the assumption that nowadays women are weaker than they were in the past is not necessary so, and the medical logic says that in light of the nutrition and medicine that we live with today, the situation is exactly the opposite.”
Thus, he disputes the lenient Halachic position stating that women in these situations must be exempt from fasting in all cases, a stance supported in the recent years by popular rabbis of the religious-Zionist persuasion.
In the book that was recently published by doctor and Rabbi Nachum Rabinowitz the head of the Ma’ale Adumim Hesder Yeshiva, a different view is presented.
In the Halachic sentence published in the yeshiva’s website, Rabbi Sherlow negates a general dismissal and instead, calls upon women in these situations to better prepare themselves for fasting.
He suggests eating fruits, drinking fluids and consuming salts while listening to their doctors’ orders.
However, Sherlow clarified that, “as each case is examined specifically, we mustn’t be too strict because this is a fast prescribed by the Rabbis.”
“Generally-speaking, those pregnant or breastfeeding are eligible of participating in the memory of the (Temple’s) destruction and on this day of fasting,” wrote Sherlow. “They must.”
“If there is a danger to the pregnancy or to the termination of breastfeeding, they shouldn’t fast as not to cause such a reality,” he said.