The story
By extension from the Biblical phrase “break the staff of bread” (Hebrew מַטֶּה לֶחֶם (maté lékhem)), staff (“long, straight rod”) in this context meaning something that acts as a support: see, for example, Leviticus 26:26 (King James Version; spelling modernized): “And when I have broken the staff of your bread, ten women shall bake your bread in one oven, and they shall deliver you your bread again by weight: and ye shall eat, and not be satisfied”; and Ezekiel 4:16: “[…] Son of man, behold, I will break the staff of bread in Jerusalem, and they shall eat bread by weight, and with care, and they shall drink water by measure, and with astonishment: […]”. Compare Egyptian ḫt n ꜥnḫ (“grain; food”, literally “stick or wood of life”).
Etymology from Wiktionary, CC BY-SA 4.0.