Development and validation of a food frequency questionnaire for national nutrition surveillance among Malaysian adolescents and adults.

Food habits vary across ethnic groups and geographical regions. However, validated dietary assessment tools accounting for such diversity remain limited. A semi-quantitative food frequency questionnaire (FFQ) was developed and validated to assess the habitual food intake of adolescents and adults across Malaysia. The 147-item FFQ was constructed using commonly consumed foods from five main ethnicities (Malay, Chinese, Indian, and Sabah and Sarawak indigenous groups) identified from national surveys. A cross-sectional validation study was conducted among purposively sampled healthy individuals aged 10-59 years from 16 administrative regions. Trained community nutritionists administered the FFQ to assess monthly intake, alongside a three-day dietary record and recall (3DRR) covering two weekdays and one weekend. Spearman's correlation, Bland-Altman plots, and quartile cross-classification evaluated the agreement between the FFQ and 3DRR for energy, macronutrients, and selected micronutrients (Vitamin C, thiamine, calcium, and iron). Respondents (n = 361; 50.3% adults, 49.7% adolescents) were 50.4% female and represented five main ethnicities (range: 15.8-25.2%), with 60.4% from Peninsular Malaysia. Energy intake estimated by the FFQ (median: 2285 kcal) was significantly higher than by the 3DRR (median: 1785 kcal; Wilcoxon p < 0.001). Spearman's correlation coefficients observed for energy (crude r = 0.31), and selected nutrients (energy-adjusted r range: 0.19-0.38), along with <10% of extreme quartile misclassification indicated acceptable ranking ability and agreement for most nutrients. Bland-Altman plots indicated no proportional bias for energy and macronutrients. In conclusion, the FFQ is a valid tool for assessing dietary intake within the multi-ethnic Malaysian population nationwide.