Xerophagy

Ze-roph-a-gee

Noun

The strictest Christian fast which is observed chiefly in the Eastern churches during Lent or especially Holy Week and in which only bread, salt, water, and vegetables may be eaten and meat, fish, milk, cheese, butter, oil, wine, and all seasonings or spices are excluded

Craig raised eyebrows when he asked for ketchup during dinner with his fiancé’s orthodox family on Good Friday.

I could not find when this term came into use in English but it comes from the Greek words from xēros meaning dry and phagein meaning to eat.