Today a lot of people say they want to eat simple, unprocessed food. Medieval people, however, might have killed for an Oreo™.
One of the biggest differences between the medieval diet (which actually continued up into the nineteenth century for most people) and the modern western diet is processed food. Unless you are taking fresh meat and fruits and vegetables and eating them after minimal cooking, you are eating processed food. We don't even think about it. In fact, a lot of what passes as "fresh, simple, healthy" food is processed. Think orange juice. It's pasteurized and has ingredients like calcium added. Think vegetable oil. How did it get from the soy bean to your bottle? Think oatmeal. Surely the oats didn't grow in the form of little flakes, and clearly something happened to it so it can cook in 5 minutes. Think sliced turkey from the deli. Have a close look at the list of ingredients. And don't even get me started on hot dogs.
Now of course processing is not automatically bad. Unpasteurized milk used to spread tuberculosis. Processing reduces spoilage. And people can have a much more varied diet when a variety of foods are available--the kind we take for granted in a grocery store, which would have left medieval people stunned (see more here). And especially processed food means that people have time to do all sorts of things during the day besides grow, gather, and prepare food. Pre-modern people, especially women, would have spent a major part of the day in food preparation. Farming, producing food, is a full-time job as any farmer will tell you, and in the Middle Ages the great majority of the population farmed.
Medieval people also ate almost entirely locally produced food, except for spices. Again, we tend not to think very much about how many of our berries come from South America, tomatoes from Mexico, peppers from Holland. And even American-grown food probably came from California. Are you in California? In the central valley? (LA and San Fran don't count). So trucks if not indeed airplanes were involved in bringing you your fresh, simple fruits and vegetables.
Here the advantage is that we can get fresh fruits and vegetables year round. Medieval people could not, unless you count parsnips and maybe cabbage as fresh fruits and vegetables. The moral of the story seems to be that we need modern technology and processing to eat a simple, wholesome diet.
I thought about this while making chocolate cake. I personally think my chocolate cake, made "from scratch," is far superior to nasty processed cake you'd buy in the store. Yes, only simple, wholesome ingredients, just like a medieval cook. First the unsweetened chocolate--whoops, it comes from the tropics of South America (and was thus unknown in the Middle Ages) and was processed from cocoa beans into handy little squares. Then butter--well, I didn't churn it, and it probably came from out of state, but it's "like" simple food. Then eggs. Eggs! Yes! Unprocessed, just sitting there. (Well, the hens were probably on a factory farm. Let's move on.) Flour is simple and wholesome--except that I didn't grow the wheat or thresh it or grind it or bleach it or put into white paper bags. Buttermilk--well, if I'd had a cow, and if I was churning my own butter (see above), I'd have buttermilk, that which is left in the churn after taking out the butter. A big if. We need some sugar--sugar cane doesn't grow around here, and the sugar in the box doesn't exactly resemble sugar cane. Let's assume we can pass baking powder off as a spice (medieval people had spice). The frosting has more chocolate, some vanilla (it's okay, it's like a spice), and powdered sugar. We already dealt with sugar--except that powdered sugar also has corn starch, which comes from corn (not a medieval plant), and doesn't look like corn on the cob. There we are! A delicious chocolate cake just like medieval people would make (except they didn't have chocolate or sugar--but they had flour!).
If they'd kill for an Oreo, just think what they'd do for chocolate cake!