The fast season of Lent was not nearly as unique in the medieval year as it is in the modern. Fast days punctuated the year, and the entire four weeks before Christmas was also a fast. Lent was merely the longest fast.
When I was young, I used to hear Catholic friends talk about choosing something to give up for Lent. In the Middle Ages, there were no such choices; they always gave up the same thing: animal products. You might think “meat,” but that only annoyed the rich. The poor never had meat anyway, and their chickpea or lentil porridges were “fast food” for every day year round. But the real problem was butter.
Butter and cheese were sheep, not cow, products, usually. In much of northern Europe, butter was the main cooking oil, not counting lard, which of course was out for Lent. Zones of Europe that depended on walnut or olive oil were less deprived, but butter regions had no solutions. Over time, their rulers bought indulgences from Popes that gave automatic forgiveness for using butter during Lent. Some cathedrals were funded by butter indulgences.
The wealthy didn’t have to give up anything except products from mammals and birds. Wine and sweets were still just fine. In theory, they ate less. In reality, their cooks just substituted almond milk for dairy and spiced the fish to match venison dishes. Fresh fish sold for a premium during Lent. By the middle of the 14th century, inland parts of Europe were so covered with fish farms (mostly for carp, a big meaty roaster of a fish) that they were getting malaria.
Monks, in richer and softer monasteries, had an out from the everlasting fast diets. Monasteries served normal food in their hospital wings, including meat. An amazing number of monks got sick during Lent.
But the prevailing attitude to the fast was deeply pious and observant, in all walks of life. No weddings were held during Lent, since weddings required feasts. Eggs were hard-boiled and saved in cold sheds, awaiting the day when they could once again be eaten. (I’ll cover Easter week when it comes around.)