Halacha forbids eating or drinking on Shabbat before reciting Kiddush, as well as eating or drinking on Mosa'e Shabbat before reciting Havdala. The question arises, if a person prepared to eat during one of these periods, and immediately after reciting the Beracha remembered that eating is forbidden, should he take a bite of the food? If he does not eat any of the food, then his Beracha will have been a "Beracha Le'vatala," a "wasted" Beracha. Should he therefore partake of some of the food to "save" his Beracha, despite the prohibition against eating before Kiddush or before Havdala?
The authorities agree that in this case, the individual should indeed partake of a bite of the food, so that his Beracha will not become a "Beracha Le'vatala." Even though Halacha forbids eating before Kiddush or before Havdala, in such a case one is told to eat a bite of the food in order to avoid transgressing the prohibition of reciting a "Beracha Le'vatala." This Halacha similarly applies in a case of a personal fast. If an individual accepted upon himself a fast, and at some point during the fast he prepared to eat, recited a Beracha, and then recalled that he is forbidden from eating, he should eat some of the food. Here, too, it is preferable that he eat a bite of food despite the prohibition that applies in order to avoid the transgression of "Beracha Le'vatala."
However, as Rabbi Moshe Halevi (Israel, 1961-2001) rules in this work Birkat Hashem, this Halacha does not apply in a case where one planned to eat and recited a Beracha before praying in the morning. If the individual remembers after reciting the Beracha that it is forbidden to eat because he has yet to pray, he should not eat any of the food, despite the fact that as a result his Beracha will become a "Beracha Le'vatala." Rabbi Moshe Halevi explains that according to the Sefer Ha'hinuch (anonymous work commonly attributed to Rabbi Aharon Halevi of Spain, 1235-1300), eating before praying in the morning constitutes a Torah violation, and therefore one should not eat in this case even in the interest of "saving" his Beracha. And even though there is a view among the Rishonim (Medieval Halachic authorities) that reciting a "Beracha Le'vatala" also constitutes a Torah violation, it cannot be determined which of these transgressions is considered more grievous than the other. Hence, when faced with such a situation, one should preferably remain passive and not partake of any of the food, given the uncertainty as to which of the two violations should override the other.
Summary: If a person recited a Beracha in preparation to eat, and then remembered that eating is forbidden because he has yet to recite Kiddush or Havdala, or because he observes a personal fast, he should take a bite of the food so that his Beracha will not have been recited in vain. If, however, one recited a Beracha in preparation to eat before praying Shaharit in the morning, he should not take a bite of the food, despite the fact that his Beracha will have been recited in vain.
