In their study the Wansink brothers examined 52 of the most famous Last Supper paintings dating from as early as the year 10,000 till 2000. They analyzed the size of the food on the table and the size of the heads in the painting. What they discovered was that the size of the entrees increased by as much as 69% while the bread increased by 66%. They concluded that as food became more plentiful in society it was reflected in the paintings of the Last Supper.
The study yielded other interesting observations. Not only did the amount of food increase, so did the variety. In one painting there is a plate of eels and basket of fluffy bread. The problem, of course, is that neither are the kind of food you would expect at a kosher celebration of the Feast of Unleavened Bread.
This study serves as a good example of how our interpretation of the Bible is often influenced by the time and culture we live in. The artists assumptions about the amount and type of food that was present at the Last Supper were influenced by the availability of food to him. All of our efforts at interpretation are conditioned by the external forces around us. It is not that these forces are bad in and of themselves. But we need to be aware of them when we read the Bible and try not to let them influence how we read the text.