Reposted from an earlier answer comparing a 14th-16th century, mostly English diet with today:

A carb heavy diet characterized by high percentage of calories comsumed through beverages, a rabid distaste for fresh vegetables, a widespread belief that food without salt was flavorless and darn near pointless, overworked college teaching assistants and residential assistants pilfering leftover food from college functions for their own consumption...oh, yeah, and young adult-heavy cities going mad for bacon. Sounds almost familiar, right? Well, maybe except for the tendency of princes to have their musicians play on a stage made out of pie crust.

This introduction is of course having some fun with generic similarities between modern "mainstream" America (my basis for comparison) and 16th century England, but it's actually a good way of getting at the differences between typical diets in modern times versus during the era between when trade with the Islamic world and parts further east was affecting the upper classes but before the foodstuffs and fads from the New World really took hold. Broadly speaking, I might say that modern diets tend to be more horizontally diverse in terms of different types of things consumed, whereas late medieval/early modern diets were more vertically efficient.

While modern carb consumption involves breads, potatoes, dry cereal, junk food, the basic 16th century staple was bread. Price controls to make at least some amount of bread affordable to even the poorest people was one of the first signs of the English government acting for the good of its people, not just the enrichment of the sovereign. Ovens in private residences were still very rare, so much like today, nearly all bread was purchased commercially. But while most bread today tends to be "white" or "wheat" (obviously not the only varieties available), the different types of bread--defined by type of grain used, fineness of flour, amount of sweetener (usually honey) and spices, etc--was so criticial that laws regulated who could bake what kind. Bakers developed "trademarks" that they carved into their bread loaves to prove it was their work, just like printers added their names to the title page of their books to claim ownership.

The #1 piece of advice for weight loss, at least for Americans, is "stop drinking your calories." And what a rainbow of ways we do that--soda, juice, a thousand varieties of alcohols and mixed drinks, milk, sweet tea, pumpkin spice lattes. For medieval people beyond the elite, drinking a high percentage of the day's calories (up to 30% in some estimates) was critical to powering through the day, but options were much narrower. While preacher railed against the evils of wine, weakened beer was the daily drink of choice for adults and children alike. (By 1500 in England, commercially-purchased beer with hops was largely replaced homebrewed ale without). This is not to say that water was "universally unsafe" or never drunk. It was the beggar's (or the penitent's) drink--free and good for hydration or religious asceticism, but vastly inferior to the beer that could also supply energy and flavor.

Although more creative options are not unheard of, American meat-eating tends to center on the big four: fish, chicken/turkey, cow, and pig. Furthermore, unlike some other modern cultures, Americans tend to consume a strikingly small percentage of each animals. Meat-eating was much more the province of the urban middle/upper and noble classes in 16C England than it is an upper class privilege today.

Fish was by far the most prevalent animal consumed, with pig and cow next up. However, standard types of fish were a much wider variety than today's typical tuna or salmon, with the occasional shrimp (or fried calamari). Studying account registers from King's College (Cambridge) in the late 15C, Francois Soyer found the students frequently dined on eel, roach, perch, tench, gudgeon, pike, herring, dogfish, salmon, mackerel, ling, cod, and oysters; haddock, sole, plaice, turbot, scallops, crab, shrimp, and sting rays were rare treats. Poultry, too, encompassed more than our default chicken and turkey. (Alas for your Renfair turkey leg, turkeys make it over from the Americas a bit later). Parish churches had built in towers for doves to nest in (yes, poop disposal was a problem)--selling young doves to hungry consumers was a common fundraising method.

Of course, for people who still maintained meatless religious fasting practices, fast days (including all of Lent) required some strategic substitions. One Italian lasagna recipe recommends substituting ground-up nuts for the meat (the recipe also involves lays of noodle and cheese; this is pre-tomato days).

In terms of pig and cow, there was a definite "waste not want not" attitude. Christopher Woolgar notes that while modern research places a premium on butchers (especially in archaeological research--a surprising amount of our knowledge of medieval meat consumption comes from studying animals skeletons in burial pits next to butcher shops), medieval sources often highlight the skills and special roles of nonprofessional English women at handling and preparing offal, especially intestines (helloooo, sausage). Pig hooves, a nice dog treat today, were considered a treat, especially among monks and nuns.

As for flavoring? With the exception of the rich and the aspirational, which I'll discuss in a moment, there were two major medieval ways of adding flavor to food: salt and fat. Our word "sauce," in fact, comes from Latin salsa and in salsamento--basically, salted. Salting meat was absolutely vital in a pre-refrigeration age, as the primary means of preservation. Salted fish, in particular, was the major way that meat was transported and consumed in winter. But pretty much everything got the salt treatment, sometimes combined with smoking. If you've guessed that salted pork, either smoked or cooked in extra fat, was as tasty then as it is now--by all accounts, thick-cut bacon was an enduringly popular way of consuming meat. (In the 19th century, in fact, travel guides for Oregon Trail pioneers recommended the purchase of absolutely unholy amounts of bacon).

By way of what we would consider flavorings, medieval culture distinguished between what scholars classify as "herbs" and "spices." The basic difference was cultural, not scientific. Herbs were local and cheaper; spices were expensive, exotic, and from far away. As a result, spices were enormously popular for the rich to dump and dump and overdump in their food, as a demonstration of conspicuous wealth and largesse to their guests (spices were also expensive medical remedies). While modern cuisine pays exquisite attention to different combinations of flavorings (spices and herbs and flavored oils and flavored vinegars and and and), medieval recipes often just say "and spices," with the implication being either that the cook would know or that the cook would just use whatever/everything that was available.

This type of pattern--vertical rather than horizontal diversity--applies to other categories of food of food as well, like dairy (milk, butter, and cheese instead of our amazing array of dairy products...but use cow, sheep, goat) and the ability of 15th-16th century foodsellers to turn anything into a pie (including the Duke of Burgundy's 28 living musicians). So while some foodstuffs would be completely recognizable to modern eyes and maybe even the modern palate (comparing taste is really hard; historians of wine tie themselves in paroxysmic fits trying to figure out what medieval and early modern wine actually tasted like), other dishes would definitely raise some eyebrows.