Apparently it was the custom of the Nephites to "assemble . . . to mourn and to fast at the burial of the chief judge" (Helaman 9:10). Bishop Diego DeLanda, a sixteenth century Mesoamerican historian, says of the Mayas:
"But when in time they came to die, it was indeed a thing to see the sorrow and the cries which they made for their dead, and the great grief it caused them. During the day they wept for them in silence; and at night with loud and very sad cries, so that it was pitiful to hear them. And they passed many days in deep sorrow. They made their abstinences and fasts for the dead, especially the husband or wife; and they said that the devil had taken him away, since they thought that all evils came to them from him, and above all death. [Milton R. Hunter and Thomas Stuart Ferguson, Ancient America and The Book of Mormon, p. 327]
“To Mourn and to Fast”
According to Stephen Ricks, both the Bible and the Book of Mormon record instances of fasting as a sign of mourning following a death. After the defeat and death of Saul and his sons, the men of Jabesh Gilead fasted seven days (1 Samuel 31:13; 1 Chronicles 10:12), as did David and his companions (2 Samuel 1:12). Similarly, public fasting occurs in the Book of Mormon in conjunction with prayer and mourning after the murder of the chief judge Seezoram (Helaman 9:10). No specific reason is mentioned in the Book of Mormon for these prayers, but they may have been to obtain solace for the living rather than mercy for the dead. Individual fasting following a death is also attested in ancient Israel (2 Samuel 3:35).
The practice of fasting as a sign of mourning following a death appears to have been a customary feature of pre-exilic Israelite religion (cf. 1 Samuel 31:13; 2 Samuel 1:12; 3:35; 1 Chronicles 10:12). However, the practice is not recorded for the post-exilic period or in the New Testament. It is also of importance that fasting as a sign of mourning is recorded in the Book of Mormon only in pre-Easter passages (so Helaman 9:10), but never following the appearance of the risen Christ to the Nephites. [Stephen D. Ricks, "Fasting in the Book of Mormon and the Bible" in The Book of Mormon: The Keystone Scripture, pp. 129-130] [For a listing and description of all references to fasting in both the Old Testament and the Book of Mormon, see the commentary illustrations for Alma 45:1; see also the commentary on Mosiah 27:22; Alma 17:3]