Is There an Obligation to Eat Bread at a Circumcision and a Wedding

To the questioner, 

This is the language of the Rema in Yoreh Deah, section 265, subsection 12:

"And anyone who does not eat at a circumcision feast is as though excommunicated by Heaven (Tosafot, chapter Arvei Pesachim), and this applies specifically when there are present there proper people; but if there are present improper people, there is no need to eat there (ibid.)."

The source of this matter is Tosafot, Pesachim (114a). And there they wrote that a "wedding feast of a Torah scholar and of a daughter of a priest to a priest" is included as well. 

And all this is based on the words of the Gemara in Pesachim (113b), which said: "And some say: one who does not recline in a company gathered for a mitzvah [is under excommunication]." 

From this it appears that any gathering of a company for some mitzvah is included.

However, there are those who hold that one does not need to eat at the meal, only to recline - that is, to sit and participate a little. (In the name of the Chazon Ish, of blessed memory).

There are also those who hold that even if one must eat, there is no obligation to eat bread, and eating mizonot is sufficient. (In the name of Rabbi Chaim Naeh, of blessed memory).

With blessings,

Rab Nahum