The day before Purim is observed as a fast day, known as Ta'anit Ester. (When Purim occurs on Sunday, the fast is observed the previous Thursday.) Several Poskim addressed the question of whether someone who got married within a week prior to Ta'anit Ester must fast on this day, and, likewise, whether those participating in a Brit Mila celebration fast on Ta'anit Ester.
Regarding a groom, the scholar Rabbi Yitzchak Tayib, in his work Erech Ha'shulchan, ruled that he does not fast on Ta'anit Ester. Rabbi Tayib draws proof to this position from a comment of the Ritva (Rabbi Yom Tov Asevilli, famous Spanish Talmudic commentator, 1250-1330), who writes that a groom must observe the four fasts commemorating the destruction of Jerusalem (Tisha B'Av, Tzom Gedalia, Asara Be'Tevet, and Shiva Asar Be'Tamuz). The Ritva explains that the groom's "Regel De'yachid," or "private festival," cannot override the "Aveilut De'rabbim," or public observance of mourning, on these fasts days, and he must therefore join in fasting. This clearly implies that a groom would be exempt from fasts that do not constitute an expression in mourning. And so, when it comes to Ta'anit Ester, which does not involve mourning, but rather (at least according to one view) commemorates the fast observed by the Jewish people before waging war against their enemies in Persia, a groom would be exempt. This is also the ruling of the Chida (Rabbi Chayim Yosef David Azulai, 1724-1806).
If a Brit Mila (circumcision) is held on Ta'anit Ester, then the three "Ba'alei Brit Avraham," that is, the infant's father, the Sandak (person who holds the child during the Mila) and the Mohel (person who performs the circumcision), are exempt from fasting. All others participating in the celebration must fast.
May the three "Ba'alei Brit Avraham" eat before the circumcision, or does the exemption take effect only after the Brit Mila?
Chacham Ovadya Yosef rules that the exemption takes effect only after the circumcision, and therefore the "Ba'alei Brit Avraham" may not eat before the Brit Mila. Rabbi David Yosef Sh’lita mentions that his father once served as Sandak on Ta'anit Ester, and he indeed refrained from eating until after the Brit Mila.
A groom, however, is exempt from fasting on Ta'anit Ester altogether, and may eat already in the morning.
Is it worthwhile for a groom or one of the "Ba'alei Brit Avraham" to be stringent and refrain from eating despite their exemption? Chacham Ovadia Yosef rules that since in these situations the groom or "Ba'al Brit" celebrates a Yom Tov (festival), it is improper to fast. This is particularly so in the case of a Brit Mila, which signifies the thirteen covenants between the Almighty and the Jewish people.
In conclusion, then, a groom within seven days of his wedding is exempt from fasting altogether on Ta'anit Ester, and when a circumcision occurs on Ta'anit Ester, the father, Sandak and Mohel may eat after the Brit Mila. In either of these cases, the individual in question should not be stringent, and should rather eat to celebrate the happy occasion.