Pooled analysis of secondary data increases the power of research and enables scientific discovery in nutritional epidemiology. Information on study characteristics that determine data quality is needed to enable correct reuse and interpretation of data. This study aims to define essential quality characteristics for data from observational studies in nutrition. To ensure interoperability of nutrition data systems, ENPADASI is developing an Ontology for Nutritional Studies (ONS). All descriptors of these study data characteristics will be made part of ONS and implemented as such in the research infrastructure. The descriptors for data quality will be mapped to existing or newly developed ontology terms. Integration of study quality characteristics with the ONS will enable the consideration of study quality during the querying of the nutrition research infrastructure and interoperability with other data systems.