sgcdonmai said: I'd put it down to her massive appetite, myself. The food that was available in England, especially back in her time, was horribly fattening.
In the UBW scenario, you get to ask Saber about what foods she likes and dislikes. She pretty much answers "I love anything well prepared." Sweet, sour, tart, bitter, salty, spicy, whatever. But when you ask her about food from her time, she kinda blanks out and gives you a look that says "You don't even want to know."
So I doubt her appetite was such a problem back then.
From what I learned in college food back then was terrible. Spices were rare, no refrigeration so food was already kinda spoiled by the time it made it to your plate, lots and lots of salt (to cover up the rotten taste), and only the rich got meat on a regular basis.