Analyzing a "vast amount of food waste" discovered during a dig at the kitchen in Durham Cathedral, archaeologists have recreated the diet of the monks and other people who lived there over the centuries (app. 14th cent - Second World War).
According to The Journal (UK), "[f]ish would have been an important part of the religious order’s diet, and the finds showed that the monks were eating North Sea cod, herring, sole, turbot, and salmon and trout from the River Wear."
Other menu items included "'white meat' calves" and "a wide range of birds" that ranged "from domestic fowl to game and wild birds from the estuaries and moors of the region." The monks may have also eaten puffins and lapwing.
Comment: This menu is necessarily incomplete because things like fruit, vegetables, bread, etc., wouldn't have been preserved after so many years, but it sounds to me like these monks and the other inhabitants of the castle ate better than most people do today. Their food was undoubtedly more healthy than today's diet of sugar-coated lard and processed "meat products" saturated with preservatives, artificial flavoring and other toxic waste.
Note: "Durham Cathedral was built in the late 11th and early 12th centuries to house the relics of St Cuthbert (evangelizer of Northumbria) and the Venerable Bede. It attests to the importance of the early Benedictine monastic community and is the largest and finest example of Norman architecture in England. The innovative audacity of its vaulting foreshadowed Gothic architecture. Behind the cathedral stands the castle, an ancient Norman fortress which was the residence of the prince-bishops of Durham." Source: UNESCO World Heritage List.