Many of the great ales of Europe originate in monastic breweries, and one of the purposes of those thick, malty brews was to help sustain the monks through periods of fasting. Odd as drinking beer while fasting may sound to modern American ears, when beer is seen mostly as a recreational drink, beer was drunk daily (often even at breakfast) in the pre-modern world as a nourishing and relatively disease-free quaff rather than an intoxicant. (Though goodness knows, a slight buzz doubtless brightened the day of many a peasant when the beer barrels were full. You need to find your job perks where they are.)
Homebrewer and beer-blogger J Wilson is tapping-into this tradition by setting out to fast on beer and water for the entirety of Lent this year, drinking a doppelbock modeled on German brews that originated in monasteries. (The most widely available of these is Pauliner's Salvator) You can follow his project at Diary of a Part-Time Monk.