This Shabad is by Bhagat Sheikh Fareed Ji in Salok Fareed Jee on Pannaa 1379
fareedhaa rottee maeree kaat(h) kee laavan maeree bhukh ||
Fareed, my bread is made of wood, and hunger is my appetizer.
jinaa khaadhhee choparree ghanae sehanigae dhukh ||28||
Those who eat buttered bread, will suffer in terrible pain. ||28||
i don't understand the metaphor or the message behind it?