Assessment of the Dutch Healthy Diet index 2015 in the Lifelines cohort study at baseline

Background: Dietary indices are useful measures to investigate associations between dietary intake and disease development. The Dutch Healthy Diet index 2015 (DHD2015-index), a measure of diet quality, assesses adherence to the 2015 Dutch dietary guidelines. We assessed the DHD2015-index in the Lifelines cohort study, and compared calculations from basic and detailed dietary intake data. Methods: Dietary intake was assessed with a specially developed Food Frequency Questionnaire (FFQ) called Flower-FFQ, which consists of one main questionnaire (heart-FFQ), which asks for intakes of major food groups, and three complementary questionnaires (petal-FFQs), which ask for detailed information on food types within major food groups of the heart-FFQ. The DHD2015-index was assessed using data from the total Flower-FFQ (for 56,982 participants), and using data from the heart-FFQ only (for 129,030 participants). Agreement between the two indices was assessed with correlation and cross-classification. Results: The median (25^th−75^th percentile) DHD2015-index score was 70 (60–80) for men and 76 (65–86) for women based on the Flower-FFQ, and 68 (58–78) for men and 73 (63–83) for women based on the heart-FFQ. The Kendall’s tau-b correlation coefficient between the two scores was 0.66. Cross-classification into quartiles of the DHD2015-index showed that 59–60% of participants were classified in the same quartile, 37% in the adjacent, and 4% in the non-adjacent. Conclusion: Dietary data from the Flower-FFQ provide the most optimal information to assess the DHD2015-index. However, the DHD2015-index from the heart-FFQ showed good agreement with the index from the Flower-FFQ of ranking participants according to diet quality, and can be used when the DHD2015 index from the Flower-FFQ is not available.