Validation of a semiquantitative food frequency questionnaire for estimation of intakes of energy, fats and cholesterol among Singaporeans

The aim of this study was to assess the relative validity of a 159-item sem iquantitative food frequency questionnaire (FFQ) for use among adult Singap oreans. This FFQ should be able to classify intakes of energy, total fat, s aturated fat, polyunsaturated fat, monounsaturated fat and cholesterol into quintiles of intakes for purposes of epidemiological studies. A total of 1 26 subjects (84 women and 42 men) took part in the study which included an interview using the newly developed FFQ (assess past month's intake) and th ree 24-h (24 h) recalls (reference method, collected over a period of 1 mon th). Subjects also collected two 24 h urinary samples for urea from which t otal nitrogen excretion was assessed to validate protein intake. When compa red to the reference method, the FFQ slighty overestimated the intakes of e nergy, total fat and types of fat as reflected by the difference in means a nd the ratio of FFQ to 24 h intakes. The overestimation ranged from 1 to 11 % of the reference method. Dietary cholesterol was underestimated by 17% by the FFQ. These differences were however, not statistically significant. Pe arson's correlation coefficients (95% confidence intervals (CI)) between in takes assessed by FFQ and reference method varied from 0.58 (0.45, 0.69) fo r total fat to 0.39 (0.23, 0.53) for polyunsaturated fat. Cross-classificat ion into quintiles resulted in correct classification into the same or adja cent quintiles in 70% of subjects, with only one or two subjects being gros sly misclassified. Nitrogen (N) intake from the 24 h recalls did not differ significantly from that estimated from the urinary nitrogen excretion. The mean (+/- SD) difference was 0.0 +/- 0.4 g and the Pearson correlation coe fficient (95% CI) was 0.55 (0.31, 0.72). It is concluded that the newly dev eloped FFQ is an adequate tool for classifying individuals' intakes into qu intiles for epidemiological studies among Singaporean adults.