[From empirical 'dietetics' to rational dietetics].

From the outset, the terms 'dietetics' and 'diet' applied in their general acceptance to all the measures, whether or not alimentary, that can provide optimal living conditions for both the healthy and the diseased. In that meaning they are synonymous with hygiene or way of life. In their more restricted acceptance, which will be used henceforth, the terms apply to the choice of food and beverages which promotes or restores health of normal and sick people. In its most restricted meaning, the term 'diet' is confined to the nutrition of the sick, consisting either in a more or less drastic limitation of food intake, or in the prescription of specific foods. Due to the absence of scientific knowledge concerning the processes of life in general, and in particular concerning the physiology of the digestive system and the metabolism, the 'dietetic' rules and principles were governed until the middle of the nineteenth century by empiricism with a strong background of intuition, tradition, magic and religion. In his continuous struggle for life, man has been confronted with the dramatic consequences of the ingestion of toxic and spoiled food. Nausea, vomiting, diarrhea, cramps and eventually death have soon been linked with the ingestion of particular food, although the symptoms were attributed to supernatural forces. Intuitively and later by laws and prohibition, the use of certain foods was to be avoided or was forbidden. Moreover, with the development of cultures and civilizations food and food intake have acquired -besides their vital necessity-social and often magic-religious values which sometimes resulted in food taboos. In most civilizations these taboos have particulars in common: they are mainly directed against food of animal origin, more against meat than fish and particularly against red meat, which is being considered as symbol of strength and power and as endowed with exciting and stimulatory properties. The meat taboos are selective for some animals or parts of an animal, but what is allowed in some cultures is forbidden in others. More or less severe and long lasting abstinence from food or fasting was also self-inflicted or imposed to individuals or whole populations by religion, sometimes seemingly on hygienic grounds but in most cases without any logic reason. Since the earliest time, diets take-together with other dietetic measures-a prevailing place in the treatment of the sick and sickness. Most alimentary prescriptions are based on a more or less drastic restriction of food and - particularly in the seventeenth century with the iatrochemical school - also of fluids. The restrictions were not only quantitative, but also qualitative with restriction of meat consumption-particularly of red meat-and the prescription of more or less diluted decoctions of barley (infusions) or broth. The numerous works on 'dietetics' published-thanks to the development of printing-from the seventeenth on through the nineteenth century concern mainly the description of foodstuffs and beverages available at the time, and of the ways of preparing them. They also provide indications concerning the way these foodstuffs can improve health and/or list which of them can be prescribed or must be avoided in the treatment of the sick and of specific diseases. Some of these 'dietetical' prescriptions and maxims seem perfectly valid from a scientific and therapeutical point of view, - at least according to our actual knowledge - however, many are totally ineffective or are ridiculous and even dangerous. Except for the "dietetical" measures imposed by public hygiene or by religion to everyone, most of the dieteticotherapeutical prescriptions (food restrictions, clysters, purgation, bleeding) involved only the small fraction of the population that could afford medical assistance. The common people - the majority - could afford neither medical help, nor food abuse - except for an occasional feast - and had only access to a limited quantity and choi