Prevention and nutrition are key issues to guarantee a healthy lifestyle and are in the kernel of the new paradigm of patient-centered medicine. A healthy diet protects against risk factors of a large number of chronic diseases and contribute to delay the disease appearance in the general population. More and more, making right diets is becoming essential from the health point of view. However, nutritionists design diets on the specific needs of each patient, using their accumulated experience and there are no well-formalized support mechanisms for such activity. The project Diet4You proposes the creation of an intelligent decision support system oriented to the adaptive and dynamic preparation of personalized diets for the specific individuals of general population, having or not, one or more diseases, by taking into account all the information available on the person. The diets will be built by considering the characteristics of the person, their health conditions, their habits and eventual drugs intake and their genetic information, which until now were not taken into account. The Diet4You tool is a hybrid system interacting several components in a complex way. One of those components is a subsystem able to compose complete menus, for a certain period of time, based on the nutritional prescriptions given by the nutritionists, in terms of balance of different families of nutrients. This component is based on a a Case-Based Reasoning (CBR) engine that adaptively creates menus with breakfast, lunch and dinner on the bases of real food databases containing dishes with their nutritional composition. In this work, this component of the whole system is presented, described and tested.