Medieval nobles ate...well, meat and bread. This was particularly important in the thirteenth century. In the late Middle Ages, the percentage of meat in the diets of urban burghers and peasants would increase for a variety of reasons. But in the high Middle Ages, consumption of meat and white (wheat) bread was a crucial signifier of noble status.

If Middle High German romance is to be taken seriously, in fact, this was all they ate: “semeln wiz, guoten win, and wildpraet” functions as a trope in descriptions of the noble table. Which is to say: white wheaten bread, good wine, and game.” Some poets, like Hermann von Aue, include fish as well.

We can’t in fact take romance as a straightforward source, obviously, but it’s a good guide to the courtly, noble ideal. Archaeological digs, chronicle sources, and household records from England, the Low Countries, and Germany back up the general impression of meat and wheat as the province of the nonility; peas, barley, vegetables, many fruits, and dairy products as associated with the lower classes.

Of course there were geographic variations. Along the Baltic and the North Sea, fish were more readily available across the social spectrum. And better quality wine was naturally cheaper in grape-growing regions, particularly in France and Italy. But the general rule seems fairly consistent.

There were a number of reasons for this division in diet. The first, as already indicated, was cost. Meat was a prestige food. With increasing forest clearance across the hih Middle Ages, hunting became a rich person’s privilege. Nobles reserved hunting AND fishing rights on their principalities to themselves—water/fishing privileges are a big deal in the demands of peasants revolting in the 15th and 16th century Holy Roman Empire. Venison and rabbits would be found on noble tables.

Meat like beef was also a privilege for the wealthy, because pasture for stock animals was so much less efficient per acre than for grain agriculture. There was some room for moderation here—pigs were more available to people in the middle and better-off lower classes, since they could just be turned loose until it was time to cook and eat them. (This was a big problem in cities, where pigs would break free and just go around eating things in sight, including the occasional baby’s arm.) But even then, salt bacon or “side of meat” would be found on the peasants’ table; fresh cuts on the nobles’.

As to vegetables, the most important and hilarious thing to keep in mind is that, for Christian Europe, salad is a Renaissance invention. Period. Raw vegetables were considered unhealthy in the medieval scientific worldview (their general interpretation of how foods affected the balance of humours in the body).

But even cooked vegetables, if household records are to be believed, made up a tiny portion of nobles’ diets at most times, famine periods being a different story altogether. One study of Westminster Abbey in the 15th century—so, basically the monastic equivalent of high aristocracy—found that one-half percent of their daily calories came from vegetables. While yes, veggies are less energy-dense than mutton or Wonder Bread, they’re not that less energy-dense.

One idea sometimes posited by scholars is that vegetables and fruits are not noted in household acdounts for nobles because they did not have to be purchased. But we don’t really see them in descriptions of dishes at feasts, either.

But as I mentioned, the romance trope is normative, not descriptive. Other prestige food stocked the castle larder: dried fruits from the Mediterranean zone, namely raisins, currents, and dates; nuts in abundance, especially for Lent (also gathered by peasants for themselves); spices like saffron and pepper. Although historians have paid the most attention to the role of spices in the late Middle Ages, at least German sources by the 13th century already point to pepper as a key distinction between noble and peasant diets. Eggs seems to be more present in recipes than as the starring role of a dish.

For elaborate feasts, the primary difference in the food intended for actual consumption would have been volume. There was no contradiction in having two different fish dishes in different courses; no division into appetizers, main courses, desserts. Just lots, and lots, and lots of food and wine. (Much of which would have been watered down...at least, that was the idea). I am source-less at present but will try to dig up some of my earlier answers where I talk about the flummoxing amount of food used in the preparation for some late medieval feasts.

So I’m sorry to disappoint you, OP, but thirteenth-century nobles would have been far more disappointed to sit down to a table of fruit salad and veggie stir-fry.