Uff da, okay I see two comments have already taken a stab at this, but I didn’t see their content before they were removed. I figure I’ll take a swing. But first, caveats!

1. I study foodways, so this question is within my wheelhouse BUT I don’t study medieval royalty specifically, so I’ll have to be looking to some sources that are new to me too.
2. This question is genuinely multi-disciplinary, because to make an accurate comparison you need someone well versed in historic nutrition/foodways and someone well versed in modern nutrition and health statistics.
3. Eating better is a tough thing to nail down, is it strictly a substantive judgment on nutritional value or are we talking relative judgements on things like flavor, variety, and quantity?
4. For an answer I am going to have to do some assumptive narrowing of the question. Medieval kings were a varied lot, with different access to foods and degrees of wealth found in, say, northwest versus southeast Europe. Similarly, poor people could produce very different results depending on who you pick – anyone below the poverty line in Canada or the bottom 1% in India live very different lives. BUT, I’m not dense, I get a sense of what you are asking, so let’s compare the nutritional value and how relatively enjoyable the variety of foods would be of a Medieval noble in England and a modern American citizen living below the poverty line (this is the data I could find). Fair?

For sourcing information about the medieval diet of elites, bioarchaeological information about nutrition (or nutritional deficits) is not particularly common, but literature about noble/elite cookery is. Per Bovey (2015), what most differentiated the diets of elites from the rest of the population was the availability of fresh meat (game, domesticates, and fish) and spices. Meat is expensive, either incurring costs to acquire it, raise it, cook it (lots of fuel) or preserve it. Moreover, many of the landscapes where wild game could be plentifully found were placed under royal control (Hanawalt & Wallace 1998).

As for spices, most of the particularly valuable ones came from outside of the country, so again, they are selective for their being cost prohibitive. Particularly popular spices were imported in small quantities over long distances from the Mediterranean for uses in spiced sauces (Bovey 2015). This also covers another aspect of Medieval noble cooking – its emphasis on variety and abundance. Feasting, as it had been in Europe since the bronze age, was an important part of being wealthy, and would have provided members of noble houses with semi-regular access to a wide variety of proteins and vegetables in plentiful quantities. Variety is one of the most important factors in a healthy diet, and – as in known by anyone stuck in quarantine currently – is a key indicator of happiness with one’s diet. So on these two fronts Medieval nobility did well for themselves. Although, an interesting note about rich diets in historic periods is that they could just as easily lead to an increase in certain health issues. Again, it is difficult to find bioarchaeological data about specific nobles rather than for populations, but the conclusions from Towle, Davenport, Irish, and Groote 2017 indicate that populations who had access to wider varieties of food may have suffered from more dental issues than populations with more plain, local diets. If we are talking about quality of life, increased nutritional diversity may be better for growing bones, but think carefully about introducing sugarcane into your diet before the advent of modern dentistry!

So let’s compare this to food variety and scarcity in modern low-income homes. In one sense, we live in a global village where the variety of cuisines (as culturally constructed related foods) one might find in a food court are more diverse than ever. A low income family might have at their disposal low-cost foods from restaurants serving food inspired by Chinese, African-creole, or Mexican cuisines. So there is certainly the appearance of variety. But from a nutritional standpoint, many foods available to low income families use the same set of limited ingredients, often preserved, and prepared as single dishes – rather than as ingredients to be used in home cooking. The data I managed to find from Nunnery, Labban, and Dharod (2017), while focusing on low-income pregnant women, puts the nail in the coffin as to the lack of nutritional variety for low income families: as income decreases, so does food security and nutritional variety. Just because you eat at panda express one day and taco bell the next does not means you have experienced actual variety.

As for the satisfaction found in low-income diets, this is a bit harder to nail down. Certainly, the US and other developed nations have long-standing subcultures that value the food habits of common people. While at the same time, modern high-status eating seems to be defined more by health than simple variety (think expensive trends like organic and gluten-free food, or the entire existence of Whole Foods). Do low income families aspire to shop/eat like an Instagram influencer on a 30-day kelp-diet purge? I need extra data, but indication from food ethnographers that I’ve read typically indicate no: class identities are ridged enough that modern Americans value what they already eat more than what they might view the elites are doing. That said, only one of those groups regularly struggles with food security.

This has been a bid meandering so let me sum up: Satisfaction is hard to pin down, but likely food insecurity on behalf of modern low-income populations (which is more common than most people realize) is enough of an issue that I’d rather be a medieval elite. However, as someone who just had major dental surgery this past summer, I’ll thank my lucky stars that I live in the here and now. As for nutrition – I welcome any specific expert takes on either Medieval foodways or modern nutrition – as far as nutritional variety goes you would also be far better off as an English, Medieval noble than as a modern, poor American.

Edit #1,314 - Make sure to also read u/allfather69's response for a more detailed take on the specifics of Medieval elite's diets!

references in order of appearance, added in edit:

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Bovey, A. 2015 The Medieval Diet, article published electronically at https://www.bl.uk/the-middle-ages/articles/the-medieval-diet

Hanawalt, B.A. & D. Wallace 1998 Medieval Crime and Social Control, University of Minnesota Press

Towle, I., C. Davenport, J. Irish, & I. De Groote 2017 Dietary and Behavioral Inferences from Dental Pathology and Non-Masticatory Wear on Dentitions from a British Medieval Town, published by the Cold Spring Harbor Laboratory, bioRxiv.

Nunnery, D.L., J.D. Labbam, & J.M. Dharod 2017 'Interralationship between food security status, home availability of vareity of fruits and vegetables, and their dietary intake among low-income pregnant women' published electronically through PubMed.gov

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As a follow up for interested readers, Carole M Counihan is a wonderful and accessible Anthropologist working on modern western foodways through many social lenses like class and gender.

This is almost certainly not true. Whilst the availability of food was somewhat limited to local produce, although not to the extent often believe, the aristocracy and royalty in particular had access to a wide variety and quantity of foods. Although this would no doubt vary depending on the region, this answer will use England as a point of reference.

Firstly, it is important to note that people in the Middle Ages had different dietary perspectives and ensuing restrictions than we do today. For example, Christianity forbade the consumption of meat during Lent, and on Fridays. These restrictions were observed to a varying extent, however the aristocracy and kingship seemingly were more strict about such matters, perhaps because they had in general greater access to alternatives. For example, after spending time in captivity after the disastrous Seventh Crusade, French knight Jean of Joinville was rebuked for eating meat on a Friday. Joinville responded by pushing away his bowl, saying he had not known what day it was, resolving to eat bread and water for the subsequent Fridays. There were also days of 'double fasting' for example, a Friday during Lent, when perhaps the religious abstained from dairy as well as meat, or subsisted solely on bread and ale. Garden produce was associated with the poor, and so was primarily eaten by the upper classes during Lent. Ciders were also primarily associated with poverty - the upper classes drank wine and ale, with wine having been a status symbol.

Despite these restrictions, the Kings of England had access to vast amounts of food. Meat and cheese were especially prized. Edward I had cheeses from the priory of Llanthony near Gloucester shipped to his household in special coffers. French cheeses were imported - four different kinds of cheese were transported to the royal household in 1242-43 by the ship of Pevensey, from Rouen. The vast majority of these cheeses were made from cow's milk, although sheep's milk was also used at times.

In the thirteenth century, the King had at least seventy royal forests from which to source meat - venison was consumed in vast quantities. These royal forests held three types of deer: red, fallow and roe, and all were eaten. Kings also gave away venison quite often; Henry III often gave over 200 deer away annually. Roe was the venison of choice, and was often given as a gift from the King to invalids. Holidays were occasions for specific types of meat: lamb was eaten on Easter, whilst boar was associated with Christmas (although not exclusively, and was a common dish at royal feasts).

Poultry was also a popular aristocratic food. Kings and aristocrats hunted for duck with hawks and falcons, and the book of St Albans from 1486 provides a breakdown of the associated hunting birds for each aristocratic class. Thrushes were eaten often among the upper classes, whilst quail was eaten less frequently. Peacocks were a common feast dish, and were served with plumage on full display at feasts. Henry III in 1249 requisitions swans, peacocks and cranes from his sheriffs in over a dozen counties, indicating that these were eaten as well. Dame Katherine of Norwich's feast on 20 January 1337 gives us further insight: her household served herons, cygnets, mallards, woodcocks, plovers, partridges, larks, and over 107 "small birds". This also changes by the season. Pigeons were eaten from late April to Mid-November, geese generally were eaten between November and February, partridge and swan was consumed primarily between late October and early March. Chicken was eaten year-round, save during Lent.

Fish was eaten on Fridays and during Lent. This was no hardship for the upper classes. Edward Stafford, third Duke of Buckingham, is on 1 May 1501 recorded as having eaten a wide variety of fish, giving indication of what was available to the upper classes during at least the early Renaissance. Stafford's household was served salt fish for breakfast, then flounders, eels, pike, salt ling, soles, plaice, turbot, half a fresh conger, and mullet for lunch. For dinner, they had further salt ling, plaice, and pike, as well as one hundred prawns. Evidently, the wealthy had access to a wide variety of fish. Although some of this was purchased or requisitioned, royal manors held fishponds as early as 1129, when records show repair work being done to the royal fishpond at Brigstock.

Although garden produce was seen as a foodstuff primarily consumed by the poor, the aristocracy had access to a wide variety of nuts, fruits and vegetables as well. Kings and nobles had gardens attached to their estates that grew a range of crops. Earl Lincoln of Holborn is recorded in 1295-96 as having grown beans, hemp, onions, garlic, pears, apples, walnuts, cherries, roses and vine stocks. Presumably the King would have access to all of these crops at the very least, and probably much more. Garden produce was also regarded as difficult to digest, especially peaches, which were said to putrefy the stomach if eaten at an early point in the meal.

Although English Monarchs did not have access to the incredible variety of foods found in a modern supermarket, by no means were they limited in quantity, variety, or quality of foodstuffs. The ability to consume multiple courses, as well as the vast estates held by the English monarchs, meant that they could consume more, and higher quality, food than the purchasing power of the poor today can afford, even in fully modernised nations.

This is my first post on this sub, from what I have seen from other answers, page numbers are not required in the answers, if necessary, I can edit this answer to provide them.

Sources:

Woolgar, C. M., Serjeantson, D., and Waldron T. Food in Medieval England: Diet and Nutrition. (Oxford: Oxford University Press, 2006).

Joinville, J. The History of Saint Louis. trans. Evans, J. (London: Oxford University Press, 1938).

Edit: Started writing this before u/sleepyscholar's comment was posted. I study Medieval History, and so don't feel qualified to post about modern food habits in any depth. His/her comment contains an excellent overview of modern eating habits.