Digital Food Frequency Questionnaire Assessing Adherence to the Norwegian Food-Based Dietary Guidelines and Other National Lifestyle Recommendations: Instrument Validation Study.

BACKGROUND: Valid assessment tools are needed when investigating adherence to national dietary and lifestyle guidelines.

OBJECTIVE: The relative validity of the new digital food frequency questionnaire, the DIGIKOST-FFQ, against 7-day weighed food records and activity sensors was investigated.

METHODS: In total, 77 participants were included in the validation study and completed the DIGIKOST-FFQ and the weighed food record, and of these, 56 (73%) also used the activity sensors. The DIGIKOST-FFQ estimates the intake of foods according to the Norwegian food-based dietary guidelines (FBDGs) in addition to lifestyle factors.

RESULTS: At the group level, the DIGIKOST-FFQ showed good validity in estimating intakes according to the Norwegian FBDG. The median differences were small and well below portion sizes for all foods except "water" (median difference 230 g/day). The DIGIKOST-FFQ was able to rank individual intakes for all foods (r=0.2-0.7). However, ranking estimates of vegetable intakes should be interpreted with caution. Between 69% and 88% of the participants were classified into the same or adjacent quartile for foods and between 71% and 82% for different activity intensities. The Bland-Altman plots showed acceptable agreements between DIGIKOST-FFQ and the reference methods. The absolute amount of time in "moderate to vigorous intensity" was underestimated with the DIGIKOST-FFQ. However, estimated time in "moderate to vigorous intensity," "vigorous intensity," and "sedentary time" showed acceptable correlations and good agreement between the methods. The DIGIKOST-FFQ was able to identify adherence to the Norwegian FBDG and physical activity recommendations.

CONCLUSIONS: The DIGIKOST-FFQ gave valid estimates of dietary intakes and was able to identify individuals with different degrees of adherence to the Norwegian FBDG and physical activity recommendations. Moderate physical activity was underreported, water was overreported, and vegetables showed poor correlation, which are important to consider when interpreting the data. Good agreement was observed between the methods in estimating dietary intakes and time in "moderate to vigorous physical activity," "sedentary time," and "sleep."