Healthy lifestyle is not only a today trend fostered by the availability of low-cost monitoring devices, but may significantly contribute to the prevention of chronic diseases as consequence of a combination of incorrect diet and lack of physical activity. In this paper, we present the use of semantic web technologies to build an architecture for supporting the monitoring of people and for persuading them to follow healthy lifestyles. Semantic technologies are used for modeling all relevant information and for fostering reasoning activities by combining user-generated data and domain knowledge. Here, we give an overview of the whole platform and highlight the structure and the role of the ontology, how it is exploited for supporting the act...