Subjects were recruited from the participants of the Isfahan Cohort Study, Iran, who had been selected through cluster random sampling among adult population aged ≥ 35 years in Isfahan, Najafabad and Arak, Iran, district in 2001.13 (link) They were followed 2 years apart for cardiovascular events assessment by telephone interview. In addition repeated measurements including behavioral, biochemical and physical characteristics were carried out in the subject who had not any events in 2007.14 (link) Among them 300 healthy volunteer aged ≥ 41 years who accepted to complete second FFQ after 2 weeks included in the current validation study. They were included if they were non-diabetic and had no history of CVD, hypercholesterolemia, renal, thyroid, hematological, or mental diseases. Those on special diets and pregnant or lactating women were excluded. Excluding all the under- and over-reporting of dietary intake (daily energy intake < 800 or > 5000 Kcal), our sample size of n = 264 was selected from this subsample.
The FFQ was completed twice; at the beginning of the study and 2 weeks thereafter. The total number of samples studied was 300. The initial FFQ was accompanied by a demographic questionnaire and a 24 h diet recall, which were administered by trained dietitian. The respondents or one of their family members were also trained to complete two self-reported diet records in the same week. The study protocol was approved by the research council of the Isfahan Cardiovascular Research Center (ICRC).
Detailed home interviews were carried out by trained health professionals at study baseline to obtain required information about participants’ general characteristics, including socioeconomic and demographic characteristics as well as data on dietary behaviors, smoking and physical activity status.15 (link),16 (link) Physical activity was assessed by means of a validated Baeck physical activity questionnaire. A trained interviewer measured standing height without shoes and recorded to the nearest 0.5 cm at the baseline visit. Body weight was measured with the subjects wearing light clothes, without shoes and recorded to the nearest 0.5 kg. Body mass index (BMI) was calculated as body weight (kg)/height (m2).
A 48-item FFQ was designed based on the nutrition questionnaire of Countrywide Integrated Non-communicable Disease Intervention program to assess usual food intakes contributing in prevention or occurrence of CVD and relevant risk factors. Face and content validity of the questionnaire were assessed by an expert panel, consisting of five nutritionists. The FFQ was tested in pilot for clarity and comprehensiveness among 30 adults who were not entered in the main study participants and had the same characteristics to study population.
Participants reported their frequency consumption of several food items over the last preceding year on a daily, weekly or monthly basis in an open-ended format. Subjects were also requested to choose the “never/seldom” response if they never consumed a given food item. The reported frequency of each food item was converted into a daily consumption. Seldom and never were calculated as “zero.”
All participants also completed a single 24 h recall and 2 food records for 3 non-consecutive days, including 2 weeks days and 1 weekend during a week. We used two dietary assessment methods as the gold standard, because completing three 24 h dietary recalls were difficult. Hence, a single 24 h recall was completed by interviewing to train participants for self-reporting 2 dietary records.
In the case of mixed dishes, to estimate the serving size of each person, the total amount of cooked food as well as the number of persons who consumed it was collected and the amount of the food intake for each person was then calculated. The participants were asked to complete two self-reported food records. If he/she was illiterate and was not able to complete the questionnaire, a family member was requested and trained to do it. The samples were followed by phone to verify and complete self-reported food records. First trained nutritionists rechecked and grouped the food items into the same 13 groups in both SFFQ and dietary reference method, which were presented intable 1 . Then, they entered the data including the frequency (time/week) consumption of foods groups based on the SFFQ and reference method, as well as the quantitative amount of food groups, intake based on dietary reference method. To estimate quantitative amount of foods intake, gram weights of food intakes were determined based on the previously established weights of the measure.17 Food groups extracted from reference dietary assessment method were similar to FFQ item.
The data were analyzed using SPSS for Windows (version 11.5, SPSS Inc., Chicago, IL, USA).The distributions of dietary intake values were examined for normality by the Kolmogorov-Smirnov test. All foods were non-normally distributed; therefore, non-parametric tests were performed. Validation of the FFQ was determined using Spearman correlation coefficients between daily frequency consumption of food groups, which assessed by the FFQ and the qualitative amount of daily food groups intake accessed by dietary reference method. Participants were divided into four groups based on frequency consumption of food groups assessed by the FFQs or dietary reference method. Then, the frequencies of subjects in the same, adjacent, one quartile apart and opposite quartiles of 2 dietary assessment methods were estimated. Intraclass correlation coefficients (ICC) were used to determine the reproducibility of 2 FFQs. P < 0.05 was considered as significant.
The FFQ was completed twice; at the beginning of the study and 2 weeks thereafter. The total number of samples studied was 300. The initial FFQ was accompanied by a demographic questionnaire and a 24 h diet recall, which were administered by trained dietitian. The respondents or one of their family members were also trained to complete two self-reported diet records in the same week. The study protocol was approved by the research council of the Isfahan Cardiovascular Research Center (ICRC).
Detailed home interviews were carried out by trained health professionals at study baseline to obtain required information about participants’ general characteristics, including socioeconomic and demographic characteristics as well as data on dietary behaviors, smoking and physical activity status.15 (link),16 (link) Physical activity was assessed by means of a validated Baeck physical activity questionnaire. A trained interviewer measured standing height without shoes and recorded to the nearest 0.5 cm at the baseline visit. Body weight was measured with the subjects wearing light clothes, without shoes and recorded to the nearest 0.5 kg. Body mass index (BMI) was calculated as body weight (kg)/height (m2).
A 48-item FFQ was designed based on the nutrition questionnaire of Countrywide Integrated Non-communicable Disease Intervention program to assess usual food intakes contributing in prevention or occurrence of CVD and relevant risk factors. Face and content validity of the questionnaire were assessed by an expert panel, consisting of five nutritionists. The FFQ was tested in pilot for clarity and comprehensiveness among 30 adults who were not entered in the main study participants and had the same characteristics to study population.
Participants reported their frequency consumption of several food items over the last preceding year on a daily, weekly or monthly basis in an open-ended format. Subjects were also requested to choose the “never/seldom” response if they never consumed a given food item. The reported frequency of each food item was converted into a daily consumption. Seldom and never were calculated as “zero.”
All participants also completed a single 24 h recall and 2 food records for 3 non-consecutive days, including 2 weeks days and 1 weekend during a week. We used two dietary assessment methods as the gold standard, because completing three 24 h dietary recalls were difficult. Hence, a single 24 h recall was completed by interviewing to train participants for self-reporting 2 dietary records.
In the case of mixed dishes, to estimate the serving size of each person, the total amount of cooked food as well as the number of persons who consumed it was collected and the amount of the food intake for each person was then calculated. The participants were asked to complete two self-reported food records. If he/she was illiterate and was not able to complete the questionnaire, a family member was requested and trained to do it. The samples were followed by phone to verify and complete self-reported food records. First trained nutritionists rechecked and grouped the food items into the same 13 groups in both SFFQ and dietary reference method, which were presented in
The data were analyzed using SPSS for Windows (version 11.5, SPSS Inc., Chicago, IL, USA).The distributions of dietary intake values were examined for normality by the Kolmogorov-Smirnov test. All foods were non-normally distributed; therefore, non-parametric tests were performed. Validation of the FFQ was determined using Spearman correlation coefficients between daily frequency consumption of food groups, which assessed by the FFQ and the qualitative amount of daily food groups intake accessed by dietary reference method. Participants were divided into four groups based on frequency consumption of food groups assessed by the FFQs or dietary reference method. Then, the frequencies of subjects in the same, adjacent, one quartile apart and opposite quartiles of 2 dietary assessment methods were estimated. Intraclass correlation coefficients (ICC) were used to determine the reproducibility of 2 FFQs. P < 0.05 was considered as significant.