The present book aims at a detailed analysis of the evolution of dietetic doctrines and an assessment of the value of medical sources for historians of food. In order to achieve the goal, the authors have analysed select medical sources composed between the 2nd and the 7th centuries AD, i.e., treatises published from the moment of canonizing die- tetic doctrine by Galen up to the composition of the medical encyclopaedia compiled by Paul of Aegina and the publication of the anonymous work entitled De cibis. Within this timeframe, there appeared a number of works which, following the assumptions of the Hippocratic school, contain a cohesive discourse devoted to the role of food in maintaining and restoring human health, thus allowing us to trace the development of diets during the period in question.