Development and evaluation of a food frequency questionnaire to assess nutrient intakes of adult women in New Zealand

Aim: In New Zealand, there are few adequate food frequency questionnaires for assessing dietary intake. This study aimed to develop and assess the relative validity of a multi-nutrient, culturally appropriate, semi-quantitative food frequency questionnaire for use in young adult New Zealand women (the New Zealand Women's Food Frequency Questionnaire (NZWFFQ)). Methods: Women (n = 110) aged 16–45 years of Māori, Pacific or European ethnicity completed a NZWFFQ assessing dietary intake over the previous month, and a 4-day weighed food record. Relative validity was evaluated by comparing nutrient intakes from the NZWFFQ with the food record using Spearman's rank correlation coefficients, cross-classification, the weighted kappa statistic and Bland–Altman analysis. Results: Nutrient intake was higher from the NZWFFQ compared with the food record for all nutrients (range: 1%–64% difference) except alcohol (−16% difference). Energy-adjusted correlations ranged from 0.23 to 0.67 (average 0.48). Correct classification into same and adjacent quartiles was over 70% for all nutrients except folate and vitamin D. Gross misclassification into opposite quartiles ranged from 1% (monounsaturated fat, magnesium, calcium) to 10% (iron). The weighted kappa showed poor agreement for vitamin D and folate, fair agreement for most nutrients, and moderate agreement for fibre, vitamin E, magnesium, calcium and phosphorus. Conclusions: The NZWFFQ overestimated intake of nearly all nutrients. While not suitable for assessing absolute intake, the NZWFFQ is suitable for ranking individuals based on nutrient intake demonstrating reasonable relative validity for this purpose.