Medieval Medicine: Why Fish Was Bad and Sugar Was Good
Fish Bad, Sugar Good and Other Medieval Ideas About Food
Medieval Europeans believed that health depended on balancing the hot, cold, wet, and dry qualities of foods. Digestion was seen as a cooking process, and the liver was thought to constantly generate blood from food. This led to surprising dietary advice: fish was considered a threat because it produced phlegm, while sugar was seen as healthy. Cooking methods and sauces were used to adjust a food's qualities, and meals were ordered from easy to hard to digest.
Sugar was very much a luxury commodity, although it became more widely available from the mid-fourteenth century—and whereas we fret about the dangers of eating too many sweet things, medieval people focused on its warm, moist qualities (which made it good for the lungs, kidneys and bladder), and saw it as a healthy option.
- Tangurena2
> In thirteenth-century England, Christians were expected to avoid meat every Wednesday, Friday and Saturday during Lent (when eggs and dairy products were also forbidden), Advent and on some saints’ days (or the eves of their feasts)
Every person (back then) could observe farm animals had sex. Since no one had seen fish having sex, it was believed that fish spawned spontaneously from rivers/lakes/oceans and therefore were free from the animal version of "original sin". That's why so much effort was put into catching and preserving fish.
Source:
https://www.amazon.com/Cod-Biography-Fish-Changed-World-eboo...
Also history of food:
https://www.amazon.com/Salt-World-History-Mark-Kurlansky-ebo...
The author has a fascination with Basques & Basque history. Or maybe they really had a large influence in fishing and trans-Atlantic navigation. And that maybe they discovered the huge cod banks by Newfoundland before John Cabot did.
https://en.wikipedia.org/wiki/John_Cabot
Medieval people were not stupid. They observed that pickled vegetables preserved the veggies for months. And they observed that people who ate pickled vegetables got scurvy (vitamin C deficiency disease) at a much lower rate. The recipes didn't travel too far, so while sauerkraut and kimchi are both pickled cabbage, with different spices they are wildly different.
- A_D_E_P_T
> "Fish Bad, Sugar Good"
> "Similarly, some fruits were safer than others: citrus fruits improved digestion, especially in hot weather, while raisins were good for the stomach, lungs and liver. And nuts were nutritious and good for the brain."
My impression is that refined sugar was extremely rare in medieval times and into the renaissance. But everybody loved raisins, and they were used extensively, even though they were usually imported from Italy and other Mediterranean regions. Various forms of raisin bread (often with dried figs, citrus peels, and currants,) were the definitive medieval festival/feast-day food. Their distant descendants are the stollen, panettone, etc., still popular as holiday treats in Europe.
Certain regions of medieval Germany (and presumably France) grew grapes but had to resort to ingenious methods to dry them into raisins: https://www.culina-vetus.de/2026/08/27/raisins-in-a-cold-cli...
- GuB-42
I am sure that in the past, good or bad food was more about conservation and food borne diseases than it was about nutrition. At least, that's the attitude that would make the most sense. That would explain sugar good / fish bad. There is probably a political aspect too, local food is seen as better than the rival neighbor food.
The modern, first world attitude must be very unusual towards history. We basically solved conservation and food born diseases are now uncommon and mostly treatable, and we have an abundance of anything, so nutrition is the only thing that remains when discussing healthy food.
What didn't change is the made up theories surrounding food. Despite all our science, we still have a lot of these today, in some for or another.
- paimapi
you have to wonder how much of these habits we see as strange now are just artifacts of
1) a lack of refrigeration (eg fruits rotting produce a much stronger odor than vegetables esp if concentrated under a fruiting tree) and
2) the revolutions we've had in agriculture wrt breeding for taste and nutrition, and the scale at which this is done now. I'm thinking specifically about the ability to quantify, isolate, and breed out the genes that result in high concentrations of phytotoxins (and the accordant pesticides that must be applied now that the natural defenses are gone)
undercooked beans contain high levels of phytotoxins, for example, and lead to gastrointestinal distress and sometimes even death. if all plants/vegetables/etc in the past had comparably elevated levels of these toxins, you can imagine that cultural associations start forming when a people start talking about whose cultivars to avoid while trying to pattern identify a reason or measure for it
the obsession with 'health' as measured by the four humors is definitely silly but the innate drive to not want to shit your guts out after your morning porridge seems like a very normal and valid motivator