An internet-based food frequency questionnaire for a large Chinese population.

BACKGROUND AND OBJECTIVES National dietary surveys are needed and difficult to conduct in China. The current study aims to develop and validate an internet-based diet questionnaire for Chinese (IDQC) to assess intakes in Northern China. METHODS AND STUDY DESIGN We recruited 292 city residents by email and telephone in Harbin to obtain the IDQC and 3-day diet diaries. The food group and nutrient intakes from the IDQC were validated against those from the 3-day diet diaries. Paired sample t-tests were used to compare the methodological differences, and repeatability was estimated using Pearson's correlations. Cross-classification was used to calculate the percentage agreement in quartiles for all food groups and nutrients. RESULTS Positive correlations were found between the IDQC and 3-day diet diaries for all food groups after energy adjustment (from 0.28 for seeds and nuts to 0.63 for dairy products). Positive correlations were observed for all nutrients between the IDQC and 3-day diet diaries, with correlations ranging from 0.37 for folic acid to 0.98 for iodine. The overall agreements for food groups and nutrients were above 69.2%, indicating satisfactory consistency between the IDQC and 3-day diet diaries. CONCLUSIONS The IDQC can be used to estimate the food and nutrient intakes in a Northern China population for both clinical nutrition epidemiological and public health nutritional purposes. The questionnaire system IDQC (v1.0) is freely available at http://www.yyjy365.org/diet/.