Unhealthy diet can lead to diseases such as diabetes, allergies, and some types of cancer, among other health-related problems. In order to help users and clinical dietitians access the relevant knowledge about food and nutrition data in e-health systems that use different data sources, ontologies about food and related domains, such as clinical medicine, individual user profile, etc., are very important in providing successful and smart e-health systems. In this paper we present an ontology-learning process using personalized dietary web services that are dealing with food-related data and knowledge rules. The result of the ontology-learning process is an OWL ontology that is developed in a semi-automatic way and can be used for the harmonization of personalized dietary web services and will enable researchers to share information in this domain. In addition, it can also use aggregated data from different sources to provide new knowledge and help people live healthier lives.