Medieval Dietetics: When Fish Was Bad and Sugar Was Good

Modern nutrition science is young, but the idea that food shapes health is ancient. Medieval European medicine, built on Galen's humoral theory, treated diet as the cornerstone of well-being. Foods were classified as hot or cold, wet or dry, and their balance determined health or illness. Digestion was a three-stage cooking process: stomach and intestines turned food into chyle, the liver refined it into blood and bile, and the blood then carried heat, moisture, and vital spirits throughout the body. Since the liver constantly generated new blood from food, you literally were what you ate.

This framework produced dietary advice that often inverts modern assumptions. Fish, now a health staple, was considered cold and wet, generating phlegm and threatening health. It was eaten for religious and economic reasons, but physicians recommended roasting or frying it, and serving it with warming spices and sauces, to counteract its dangers. Sugar, meanwhile, was a luxury that became more available from the mid-fourteenth century and was prized for its warm, moist qualities—good for lungs, kidneys, and bladder. Medieval people did not fret about sugar; they saw it as healthy.

Meat and produce were judged similarly. Chicken was the safest meat: moderately warm, easily digestible, ideal for the sick and wealthy. Beef was coarse, produced thick blood, and suited only manual laborers. Pork and lamb were nutritious, but duck, goose, and venison were hard to digest and best avoided. Vegetables were ambivalent: cabbage caused melancholy and nightmares, lettuce was dangerously cold and moist, and beans caused flatulence and confusion. Fruits like apples and cherries were cold and moist, producing putrid humours, but cooking made them safer. Nuts were good for the brain, and citrus aided digestion.

Cooking was not just about taste; it was applied dietetics. Boiling could moisten dry beef, roasting could dry moist pork, and frying onions reduced their excessive moisture. Sauces and spices served medical as well as culinary purposes—sharp, vinegary sauces stimulated appetite, and saffron comforted the heart. Even meal order mattered: start with confections to open the stomach, serve digestible dishes first, and close with candied ginger or spiced wine.

This system was not mere superstition. It was a coherent, if flawed, model that connected food to health in an era before germ theory. It also shows that dietary advice is culturally and scientifically contingent—what seems obvious today may look absurd tomorrow.