Food at the Last Supper in picture

I find this interesting:
Food culture and the Last Supper | Culture Making:

"From the 52 paintings, which date between 1000 and 2000 A.D., the sizes of loaves of bread, main dishes and plates were calculated with the aid of a computer program that could scan the items and rotate them in a way that allowed them to be measured. To account for different proportions in paintings, the sizes of the food were compared to the sizes of the human heads in the paintings. The researchers' analysis showed that portion sizes of main courses (usually eel, lamb and pork) depicted in the paintings grew by 69 percent over time, while plate size grew by 66 percent and bread size grew by 23 percent."

What I'm thinking about is why this should be. I can think of two or three possible reasons but not yet decide between them.
One of the reasons could be that, rather like the following of social fashion around the production of the painting, the portions are reflecting a greater wealth in society. However, that doesn't necessarily work; these works would have been commissioned by the rich and they probably didn't have stingy portions. But then, how would the painter have viewed that ....

Which brings into play another line of explanation: culture, but culture of depiction. Perhaps it could be to do with ideological considerations about what amount of food one should portray saints as eating. In a culture which values the ascetic, small portions would presumably be regarded as more seemly than large. However, that probably doesn't entirely do it either: ascetic attitudes continued through quite large chunks of this period and yet, presumably, the increase continued.

Perhaps it's a bit of both these explanations? A change from portraying ascetic ideals to reflecting actualities. This would fit, to some degree, with the shift to humanism; observation of the actual, valuing of human life as lived, desire by patrons to display wealth ... yes, that sounds plausible at first sight ...
What do you reckon?

PS more recently, a helpful response article on this...