Development and evaluation of an index assessing adherence to the Norwegian food-based dietary guidelines: the Norwegian Dietary Guideline Index (NDGI)

Background: Monitoring adherence to the Norwegian food-based dietary guidelines (FBDGs) could provide valuable insight into current and future diet-related health risks. The aim of this study was to develop and evaluate an instrument for measuring adherence to the Norwegian FBDGs as a tool in nutrition surveillance, which can be suitable for inclusion in large public health surveys covering multiple health- and lifestyle factors. Methods: : A Norwegian Dietary Guideline Index (NDGI) was designed to reflect adherence to the Norwegian FBDGs on a scale from 0-100, with a higher score indicating higher adherence. Dietary intakes were surveyed by 19 questions, reflecting 15 dietary components covered by the Norwegian FBDGs. The NDGI was applied and evaluated using nationally representative dietary data from the cross-sectional web-based Norwegian Public Health Survey among 8,558 adults.​ Results: : The population-weighted mean NDGI score was 65 (SD 11), and the scores were normally distributed across a range of 21-99. Mean score varied with background factors known to be associated with adherence to a healthy diet, for example women scored higher than men (67.2 vs 63.5) and the score increased with age in both sexes. The index was multidimensional and captured various dietary patterns that contribute to a healthy diet. Conclusion: The NDGI is a compact tool for assessing diet that may be used for monitoring trends in adherence to the Norwegian FBDGs, to identify target groups for interventions, and for priorities in public health policies.​ The tool is transparent and flexible and may as such be applicable in other countries or settings with similar guidelines.