Fascinating discussion on a topic I've spent a great deal of time studying. There are a number of things to consider about the medieval diet that potentially had an edge, in terms of health benefits, over our own.

* Dairy products played a minor role in the diet, replaced mainly by almond "milk" and bread crumbs for thickening. These people understood that adult human beings weren't designed to be consuming large amounts of dairy on a daily basis, so they consumed it moderately (no "four-cheese pizzas" for them.) And of course, any dairy they did consume was free from hormones, antibiotics, etc.
* Meat consisted of either wild game or free-range, grass-fed animals, much more nutritious and free from all the crap we have nowadays.
* Seafood didn't have the problems of mercury contamination.
* Bread (at the peasant level at least) was usually whole grain.
* No problems of pesticides in produce.
* No chemical additives of any kind.
* Little or no salt.
* No such thing as deep-frying in oil.
* Much smaller portions than the average diet in the modern industrial world.
* Meals were important sit-down family events, to be consumed slowly, not in a rush in your car on your way to work.
* And of course, last but definitely not least, FAR more exercise to work off whatever calories they did consume.

The downside? Probably much less than optimal vegetable and fruit consumption, based on limited availability, especially in northern climates. So diseases did crop up as a result of the lack of these nutrients.

As for their alchohol consumption, I expect that overall it was far less than ours, when you figure out the actual alcohol content of what they drank, as previous posters have mentioned.