Relative Validity and Reproducibility of a Short Food Frequency Questionnaire to Assess Nutrient Intakes of New Zealand Adults

There is no recent validated short food frequency questionnaire (FFQ) for use in New Zealand (NZ) adults. This study aimed to evaluate the relative validity and reproducibility of a short FFQ in free-living NZ adults aged 30-59 years. A 57-item, semi-quantitative FFQ was developed and pre-tested. During a 12-month study period the FFQ was administrated twice with a 9-month interval between administrations. Four two-day diet records were collected at months 0, 3, 6, and 9 and a blood sample was taken at month 9. Spearman correlations were used to evaluate the validity of the FFQ with the eight-day diet records and selected biomarkers. Cross-classification analysis and the Bland-Altman method were used to assess the agreement between the FFQ and the diet record. Reproducibility over nine months was assessed using intra-class correlations. A total of 132 males and females completed both FFQs, the eight-day diet record, and provided a blood sample. The highest energy-adjusted correlation coefficients were observed for alcohol (0.81), cholesterol (0.61), and carbohydrate (0.61), with the lowest for sodium (0.29), thiamin (0.33), and niacin equivalents (0.34). More than three quarters of the participants were correctly classified into the same or adjacent quartile for most nutrients, with a low proportion of participants being grossly misclassified (<10%). For most nutrients, the limits of agreement from the Bland-Altman analyses were between 50% and 250%. A positive correlation was observed between dietary intakes and plasma biomarkers for all selected nutrients. The FFQ showed moderate to good reproducibility, with almost all reliability coefficients ranging from 0.60 to 0.80. This short FFQ was shown to validly and reliably rank individuals by their habitual intake of most major nutrients, indicating that the FFQ will offer a time-efficient way to assess the nutrient intake of NZ adults in future research.