Validity and reliability of a food frequency questionnaire for assessing dietary intake among Shanghai residents.

Background: Few localized food frequency questionnaires (FFQ) have been developed and used in Chinese nutrition surveys despite China's large population and diverse dietary habits.

Method: We analyzed data collected in two waves (six months apart) of the Shanghai Diet and Health Study in 2012-2013, from 1623 Shanghai residents (798 men and 825 women) older than 18 years. The results of 3-day 24-h dietary recalls (HDR) plus condiment weighing were used to evaluate the validity and reliability of the SDHS FFQ.

Results: The median and first and third quartiles for energy intake (in kcal) derived from the FFQ1 and FFQ2 were 1566.5 (1310.1-1869.6) and 1561.9 (1280.2-1838.4), respectively, of which protein (in g) was 54.3 (42.5-65.8) and 52.9 (42.4-64.5), fat (in g) was 49.8 (37.2-64.7) and 47.9 (34.9-61.9), and carbohydrates (in g) was 227.3 (180.8-277.9) and 228.1 (182.2-275.2) in the reliability analysis. The median and first and third quartiles for energy-intake differences between the FFQ1 and the 3-day 24-HDR with condiment weighing was 59.3 (- 255.5-341.6), of which protein was - 5.2 (- 18.7-7.8) and fat was - 11.2 (- 30.8-5.3). The adjusted Spearman's correlations were 0.33-0.77 for validity and 0.46-0.79 for reliability. The intra-class correlation coefficients exceeded 0.46 (validity) and 0.47 (reliability) for macronutrient intake. The consistency between the same and adjacent quartiles was approximately 80% for various nutrients.

Conclusion: The reliability and comparative validity of the SDHS FFQ is similar to FFQs that are used worldwide.