Validation of a short food frequency questionnaire to assess consumption of cereal foods, fruit and vegetables in Chinese Singaporeans

Objective: To assess the ability of a 16-item food frequency questionnaire (FFQ) to measure consumption of cereal foods, fruit and vegetables in Chinese Singaporeans. Design: Subjects completed the questionnaire twice, at the beginning and end of a six-week period during which they also provided three 24 h diet recalls. Estimates of intake from the questionnaire were compared with those from diet recalls. Subjects: Subjects were recruited from a range of occupational groups through random sampling across divisions in the headquarters of the Singapore Ministry of Health. Of the 81 subjects initially recruited, three failed to complete the diet recalls, one was excluded due to changes in diet, and seven did not return the second questionnaire. Results: Mean difference in food group consumption estimated by the two methods did not differ significantly from zero for fruit (0.00 serving, s.d. = 0.54, 95% CI = -0.13, +0.12, P = 0.95) or vegetables (-0.05, s.d. = 0.29, 95% CI = -0.12, +0.02, P = 0.13). For cereal foods, the mean difference was small, but significantly different from zero only in women (-0.32 servings, s.d.=0.92, 95% CI = -0.59, -0.06, P = 0.02). At an individual level, cereal food intake as measured by the FFQ may be 37% below or 59% above the diet recall values; and values for total fruit and vegetables may be half or double the recall values. Among subjects whose intake was classified into the lowest quartiles by diet recalls, 78% and 94% respectively, fell into the lowest two questionnaire quartiles for cereal foods, and total fruit and vegetables. The ability of the questionnaire to predict those having inadequate intake based on recall data was more than 90% for the three food groups. Conclusion: The short questionnaire cannot replace the three-day recalls in intake assessment for individuals, bur it could be used to screen for low consumers in intervention programmes, to assess mean food group intake in population groups, and to rank individuals into broad categories of food group intake.