Relative Validity and Reproducibility of a Food Frequency Questionnaire to Assess Food Group Intake in Pregnant Jordanian Women

BackgroundResearch on the relationship between maternal diet and pregnancy outcomes requires valid dietary assessment tools in pregnancy.ObjectiveThis study aimed to develop and examine the relative validity and reproducibility of a quantitative food frequency questionnaire (FFQ) to estimate food group intake in a sample of pregnant Jordanian women.DesignIn this validation study, food group intake from a culturally sensitive quantitative FFQ was compared with food group intake from three 24-hour dietary recalls.Participants and settingThe validation study was conducted from 2015 to 2017 at the maternity clinics in Jordan University Hospital among 131 healthy singleton pregnant Jordanian women. Of these women, 30 also took part in the reproducibility phase, which involved repeated completion of the FFQ in a time frame of 1 month. Pregnant women who had gestational diabetes, preeclampsia, and chronic diseases were excluded.Main outcome measuresRelative validity and reproducibility of a 117-item quantitative FFQ used to estimate usual food intake over a period of 1 month.Statistical analyses performedIntraclass correlation coefficients and weighted κ statistics were calculated to test the reproducibility between the two administrations of the FFQ. Pearson correlations were estimated to validate the FFQ against 24-hour dietary recalls. Cross-classification and Bland-Altman plots were used to examine the agreement between the two dietary assessment methods.ResultsThe intraclass correlation coefficients between the two FFQs ranged from 0.24 for legumes to 0.93 for processed meats. A moderate level of agreement was observed between two FFQs. De-attenuated and energy-adjusted correlations ranged from 0.08 for sweets and sugar to 0.93 for sugary drinks. On average, 50.9% and 45.2% of participants were classified by the FFQ and the 24-hour dietary recalls into the same quartile based on their crude and energy-adjusted food group intake, respectively. Bland-Altman plots showed satisfactory agreement between two methods for most food groups.ConclusionsThe FFQ showed moderate reproducibility and good relative validity for most food groups.     

Validity of a Food Frequency Questionnaire in Assessing Nutrient Intakes of Low-Income Pregnant Women

Objective: In 1989, a validation study of eight nutrients was performed on a modified food frequency questionnaire (FFQ) specifically designed for low-income pregnant women. The purpose of this study was to broaden the scope of the previous study by assessing the validity of the FFQ for 17 additional nutrients. Methods: The Pregnancy Food Frequency Questionnaire (PFFQ) was administered to a sample of 295 low-income, pregnant women aged 14–43 years living in Massachusetts. A randomly selected subsample of 101 women who provided at least one diet recall and reported intake of less than 4,500 calories were included in this analysis. Results: Mean intake of 25 nutrients as assessed by one administration of the PFFQ and up to three diet recalls collected over 1 month were similar. Unadjusted correlation coefficients between nutrient intake measured by diet recalls and the questionnaire ranged from .28 (carotene) to .61 (folate). After adjusting for energy intake the correlations ranged from .03 (B12) to .46 (folate). The correlations corrected for day-to-day variation were higher, ranging from .07 (B12) to .90 (zinc). The mean correlation was .47 and there were 54% over .40. Conclusions: A food frequency questionnaire for English-speaking, low-income, pregnant women can provide maternal and child health practitioners and researchers a valid estimate of diet across a wide range of nutrients.     

Development of an interview-administered food-frequency questionnaire for use amongst women of South Asian ethnic origin in Britain

Objectives: To develop an interview-administered food-frequency questionnaire (FFQ) to assess usual long-term intake of foods and nutrients amongst women from the largest South Asian communities residing in Britain. Methods: A list of foods and dishes consumed by these South Asian communities was compiled from data collected in previous studies. Foods which contributed to interindividual variation in the intake of the various macronutrients or were rich in fat or fibre were included in the FFQ. Portion size for traditional foods were estimated using sets of eight colour photographs. A nutrient database was modified to make it appropriate for South Asian diets. The reliability of the FFQ was assessed in a group of volunteer South Asian women (n=14) of differing regional and religious backgrounds. A preliminary validation exercise was conducted in a group of Punjabi Muslim women (n=11) who had kept 7-day weighed records 2 years previously. Results: The reliability of this FFQ was high, with most women being classified in the same tertile for energy and macronutrient intake in the two interviews. The main sources of energy and macronutrients identified by the FFQ were similar to those identified by the weighed records but the average nutrient intakes estimated by the FFQ were slightly higher. The level of agreement between the two dietary methods, measured by the ability of the FFQ to classify women in the same tertile of intake as the weighed records, was high for percentage energy intake from fat, protein and carbohydrates, but less so for absolute nutrient intakes. These results were, however, limited because of the small sample size. Conclusions: This is the first FFQ specifically designed for South Asian communities in Britain. Despite the diversity of diets, these preliminary findings suggest it will be a useful and easy to administer tool in chronic disease epidemiology to obtain standardized information on long-term usual dietary intake from these communities. A more comprehensive validation of this FFQ is now underway.     

Food Frequency Questionnaires and Overnight Urines Are Valid Indicators of Daidzein and Genistein Intake in U.S. Women Relative to Multiple 24-h Urine Samples

Data regarding convenient, valid methods for measuring U.S. isoflavone intake are limited. We evaluated a soy food questionnaire (SFQ), the Willett food frequency questionnaire (FFQ), and overnight urine samples relative to excretion in 24-h urine samples. We also described intake among women in a high-risk program for breast or ovarian cancer. Between April 2002 and June 2003, 451 women aged 30 to 50 yr with a family history of breast or ovarian cancer completed the SFQ and FFQ. Of them, 27 provided four 24-h and overnight urine specimens. In these women, 24-h sample measures were correlated with SFQ estimates of daidzein (Spearman r = .48) and genistein (r = .54) intake, moderately correlated with the Willett FFQ (daidzein r = .38, genistein r = .33), and strongly correlated with overnight urine excretion (daidzein r = .84, genistein r = 0.93). Among all 451 SFQ respondents, mean (median) daidzein and genistein intakes were 2.8 (0.24) and 3.9 (0.30) mg/day. Primary sources of both were soymilk, soy nuts, and tofu. We conclude that targeted soy food questionnaires, comprehensive FFQs, and multiple overnight urines are all reasonable options for assessing isoflavone intake in epidemiologic studies.     

Validity of the Willett food frequency questionnaire in assessing the iron intake of French-Canadian pregnant women

ObjectiveMaternal intake is crucial to pregnancy outcomes. Evidence shows that both nutrient deficiency and excess can have adverse effects. In pregnancy, changes in iron metabolism occur; therefore, dietary reference intakes increase to support expansion of red cells and maternal–fetal transfer of iron. Appropriate and valid assessment tools are required to investigate nutritional concerns in mothers with and without gestational diabetes mellitus (GDM). The objective of this study was to assess the Willett food frequency questionnaire (FFQ) to assess iron intake in women with (n = 15) and without (n = 45) GDM.MethodsTo validate the modified FFQ, estimated total iron intake during the third trimester was compared with biomarkers of iron status such as serum ferritin, soluble transferrin receptor (sTfR), and the sTfR:F index at delivery. Data were tested for normality using the D’Agostino-Pearson test. Differences between groups were tested using t tests or Mann–Whitney tests. Correlations were tested using Spearman’s ρ. Significance was set at P < 0.05.ResultsSignificant crude and energy-adjusted serum ferritin and total iron intake were related (ρ = 0.30; P < 0.05) in women without GDM. Serum ferritin, sTfR, and the sTfR:F index were different (P < 0.05) between women with intakes above and below the recommended levels. Cross-classification showed agreement between methods in mothers with and without GDM; on average, 63% of the women were classified into the same or adjacent quartile when ranked by FFQ and iron status.ConclusionThese findings suggest the Willett FFQ is a good tool for assessing total iron intake of French-Canadian pregnant women.     

Seasonal variations in dietary intake affect the consistency of dietary assessment

Background: Nutritional epidemiology studies are usually based on one dietary assessment without taking into account the season in which the interview is taken or adjusting for the difference in reporting dietary intake in different seasons. The semiquantitative food frequency questionnaire has become the primary questionnaire method for measuring dietary intake in epidemiological studies. The aims of this report were (a) to evaluate the effect of season on dietary intake as measured by a semiquantitative food frequency questionnaire (FFQ) conducted twice: once in summer and a second time in winter; and (b) to assess the effect of the differences in dietary intake on biochemical and anthropometric seasonal related changes, such as serum cholesterol and body mass index (BMI). Population and methods: The study population consisted of 94 male industrial employees who participated in clinical biochemical and physical examinations as well as evaluation of their dietary intake twice a year. Dietary intake was assessed using the semiquantitative FFQ that included 96 items and was conducted by a personal interview. Results: We found a significant increase in the intake of selected nutrients in winter as compared to summer as well as an increased intake of animal fat-containing foods such as meat and dairy products. Significant correlation coefficients were shown between the increase in dietary intake of saturated fat and the increase in BMI, serum total and LDL cholesterol. The increase in dietary cholesterol was significantly and positively correlated with the increase in serum total and LDL cholesterol. Conclusion: Although FFQ are designed to assess average yearly food intake, we identified significant seasonal changes in dietary intake as measured by FFQ. These changes have a health impact on our population.     

Validity and reproducibility of a food frequency questionnaire for pregnant Finnish women

The authors developed a self-administered 181-item food frequency questionnaire (FFQ) to assess dietary intake during pregnancy for Finnish women from August 1995 to July 1996. In the validation study (n = 113), the data that were collected by using two 5-day food records completed during the eighth month of pregnancy were compared with FFQ data. The intake of foods and nutrients was higher as determined by FFQ than that assessed using food records. Pearson correlation coefficients for nutrients, after adjustment for energy, ranged from 0.19 (vitamin E) to 0.70 (thiamin) and, for foods, from 0.03 (high-fat milk) to 0.84 (low-fat milk). Energy adjustment improved the correlations for nutrients. Correction for attenuation improved correlations for both foods and nutrients. On average, 70% of the foods and 69% of the nutrients fell into the same or adjacent quintiles, according to the FFQ and the food record. In the reproducibility study, 111 women completed the FFQs twice at a 1-month interval. The intraclass correlation coefficients for nutrients ranged from 0.42 (ethanol) to 0.72 (sucrose, riboflavin, and calcium), and for foods, they ranged from 0.44 (ice cream) to 0.91 (coffee). The authors conclude that the FFQ has an acceptable reproducibility and represents a useful tool for categorizing pregnant women according to their dietary intake.     

Reproducibility and Validity of a Food Frequency Questionnaire among Vietnamese in Ho Chi Minh City

Objective: Our objective was to assess the reproducibility and validity of a food frequency questionnaire (FFQ) among individuals living in Ho Chi Minh City, Vietnam.

Methods: A total of 116 food items in our FFQ were selected by ranking food items according to their contribution to the population intake of nutrients, based on multiple 24-hour recalls (24HRs) from 144 participants in July 2001. The FFQ was validated by using three 24HRs for 118 men and women in Ho Chi Minh City, Vietnam in August 2002. The reproducibility of the FFQ was assessed by repeated administration at 7 ± 3.4 days.

Results: The reproducibility study showed that Spearman correlation coefficients, adjusted for energy intake, ranged from 0.47 to 0.72, and that weighted kappa values ranged from 0.42 for lipid to 0.65 for potassium. In the validation study, correlation coefficients, adjusted for energy intake, between the FFQ and the 24HRs ranged from 0.16 (calcium) to 0.45 (retinol). The proportion of subjects classified by the FFQ into the same third as determined by the 24HRs was between 42% and 62%.

Conclusions: This food frequency questionnaire measured the usual intake of major nutrients for Vietnamese adults living in Ho Chi Minh City and its urban area, where dietary patterns are similar to those of the Vietnamese population.     

Validation of a soy food frequency questionnaire with plasma concentrations of isoflavones in US adults

OBJECTIVE: To validate assessment of soy intake using food frequency questionnaires (FFQs) compared with plasma isoflavone (genistein and daidzein) concentrations. DESIGN: Cross-sectional analysis of soy isoflavone intake and plasma analysis of isoflavones. SUBJECTS: 77 men and women, age range 20 to 40 years, recruited from the Seattle metropolitan area. MAIN OUTCOME MEASURES: Isoflavone intake was determined from responses to a 40-item soy FFQ and from tofu and soymilk intake assessed as part of a comprehensive FFQ used for the Women's Health Initiative (WHI FFQ). Isoflavone concentrations in fasting blood samples were determined by liquid chromatography-mass spectrometry. STATISTICAL ANALYSES: Correlation coefficients were calculated for: a) isoflavone intake assessed by the soy FFQ and the WHI FFQ, b) intake assessed by the soy FFQ and plasma isoflavone concentrations, and c) intake assessed by the WHI FFQ and plasma isoflavone concentrations. RESULTS: Isoflavone intake was highly correlated between the soy FFQ and the WHI FFQ (r = 0.84). Genistein and daidzein intakes determined by the soy FFQ were significantly correlated with plasma concentrations (r = 0.53 and 0.45, respectively). Isoflavone intake assessed from the WHI FFQ was also correlated with plasma concentration (r = 0.46 and 0.45). Soymilk and tofu were the two major contributors to isoflavone intake (38.6%). CONCLUSIONS: A soy-specific, 40-item FFQ assessed isoflavone intake with good validity. Isoflavone intake assessed by the WHI FFQ (tofu and soymilk) had lower correlations with plasma concentrations compared with the soy FFQ. Nonetheless, assessment of the two foods is a reasonably good marker for soy food consumption in this sample.     

Assessment of Pre-Pregnancy Dietary Intake with a Food Frequency Questionnaire in Alberta Women

Purpose: Pre-pregnancy is an under-examined and potentially important time to optimize dietary intake to support fetal growth and development as well as maternal health. The purpose of the study was to determine the extent to which dietary intake reported by non-pregnant women is similar to pre-pregnancy dietary intake reported by pregnant women using the same assessment tool. Methods: The self-administered, semi-quantitative food frequency questionnaire (FFQ) was adapted from the Canadian version of the Diet History Questionnaire, originally developed by the National Cancer Institute in the United States. Pregnant women (n = 98) completed the FFQ which assessed dietary intake for the year prior to pregnancy. Non-pregnant women (n = 103) completed the same FFQ which assessed dietary intake for the previous year. Energy, macronutrients, and key micronutrients: long-chain omega-3 fatty acids, folate, vitamin B₆, vitamin B₁₂, calcium, vitamin D and iron were examined. Results: Dietary intake between groups; reported with the FFQ; was similar except for saturated fat; trans fat; calcium; and alcohol. Pregnant women reported significantly higher intakes of saturated fat; trans fat; and calcium and lower intake of alcohol in the year prior to pregnancy compared to non-pregnant women who reported intake in the previous year. Conclusions: Despite limitations; a FFQ may be used to assist with retrospective assessment of pre-pregnancy dietary intake.     

Absorption estimates improve the validity of the relationship between dietary and serum lycopene

ObjectiveStudies show low correlations between dietary intake and serum concentrations of lycopene, which make it difficult to assess the effectiveness of dietary interventions with this phytonutrient. We hypothesized that 1) combining food-frequency questionnaires (FFQs) and 3-d diet records (3D-DRs) by the triads method would improve the validity of this relation and 2) correcting dietary information for differences in lycopene absorption from food matrices would further improve validity.MethodsWe measured dietary intakes of lycopene from 49 adults by 3D-DR and FFQ. Serum lycopene was measured by high-performance liquid chromatography with diode array detection. Cholesterol and triacylglycerol concentrations were measured spectrophotometrically. Lycopene-containing foods were given absorption factors based on literature and laboratory values. Associations between dietary and serum lycopene were modeled using multiple regression. The triads method was used for validation of relations among FFQ, 3D-DR, and serum lycopene.ResultsRaw data showed low correlations between dietary and serum lycopene (r = +0.15 for 3D-DR, +0.35 for FFQ). Mathematical modeling showed that the 3D-DR and FFQ methods must be used to collect accurate dietary information for lycopene. Validity coefficients calculated by the triads method were +0.34 for 3D-DR and +0.78 for FFQ. Correcting for absorption increased the validity coefficient to +0.72 for 3D-DR and from +0.45 to +0.66 for serum lycopene.ConclusionThe relation between dietary intake and serum concentrations of lycopene and other carotenoids can be improved by collecting 3D-DR and FFQ data and by adjusting dietary information for nutrient absorption.     

N-Nitroso Compounds: Assessing Agreement between Food Frequency Questionnaires and 7-Day Food Records

BackgroundN-nitroso compounds are recognized as important dietary carcinogens. Accurate assessment of N-nitroso intake is fundamental to advancing research regarding its role with cancer. Previous studies have not used a quantitative database to estimate the intake of these compounds in a US population.ObjectiveTo address this gap, a database of N-nitroso values was developed in conjunction with an existing food frequency questionnaire (FFQ). In this article we report on the relative validity of the FFQ instrument modified to estimate intake of N-nitroso compounds.DesignIntake estimates of 23 N-nitroso compounds from the FFQ were compared with those from 7-day food records in a cross-sectional study conducted from January 2005 through June 2006.SubjectsA sample of 98 healthy adult subjects (aged 50.42±12.84 years) completed an FFQ and then recorded foods and beverages consumed on 7-day food records.ResultsCrude and energy-adjusted N-nitroso compounds intakes were significantly higher in the FFQ than the 7-day food records (P<0.001). Spearman correlations for crude and energy-adjusted N-nitroso intakes ranged from 0.004 to 0.48. By tertiles of N-nitiroso compounds, there was moderate agreement (κ>0.30) for five compounds. Higher estimates of N-nitroso compounds by FFQ was explained by a greater proportion of subjects who reported eating foods high in N-nitroso compounds on FFQ than reported on 7-day food records.ConclusionThe modified FFQ with N-nitroso values is a useful tool for assessing N-nitroso intakes relative to a group, and captures all food items with N-nitroso compounds, including those foods with high concentrations and eaten sporadically.     

Evaluation of the Validity of a Food Frequency Questionnaire and 24-Hour Dietary Recall to Assess Dietary Iron Intake in Children and Adolescents from the South American Youth/Child Cardiovascular and Environmental Study

BackgroundA food frequency questionnaire (FFQ) for South American children and adolescents was developed, but its validity for assessing dietary iron intake has not been evaluated.ObjectiveTo evaluate the validity of the FFQ and 24-hour dietary recalls (24h-DR) for assessing dietary iron intake in children and adolescents.DesignThe South American Youth/Child Cardiovascular and Environmental study is a multicenter observational study, conducted in five South American cities: Buenos Aires (Argentina), Lima (Peru), Medellin (Colombia), Sao Paulo, and Teresina (Brazil). The FFQ assessed dietary intake over the previous 3 months, and the 24h-DR was completed three times (2 weekdays and 1 weekend day) with a minimum 5-day interval between recalls. Blood samples were collected to assess serum iron, ferritin, and hemoglobin levels.Participants and settingData of 99 children (aged 3 to 10 years) and 50 adolescents (aged 11 to 17 years) from public and private schools were collected during 2015 to 2017.Main outcome measuresDietary iron intake calculated from the FFQ (using the sum of daily iron intake in all food/food groups) and 24h-DR (mean of 3 days using the multiple source method).Statistical analyses performedDietary iron intake in relation to blood biomarkers were assessed using Spearman rank correlations adjusted for sex, age, and total energy intake, and the quadratic weighted κ coefficients for agreement.ResultsSpearman correlations showed very good coefficients (range = 0.78 to 0.85) for the FFQ in both age groups; for the 24h-DR, the coefficients were weak in children and adolescents (range = 0.23 to 0.28). The agreement ranged from 59.9% to 72.9% for the FFQ and from 63.9% to 81.9% for the 24h-DR.ConclusionThe South American Youth/Child Cardiovascular and Environmental study FFQ exhibited good validity to rank total dietary iron intake in children and adolescents, and as well as the 24h-DR, presented good strength of agreements when compared with serum iron and ferritin levels.     

Validation of a short food frequency questionnaire to assess folate intake

A short quantitative food frequency questionnaire (FFQ) to assess folate intake was developed and validated against a 7-d weighed food intake record (7d-WR) and biochemical indices of folate status. Thirty-six men and women completed the self-administered FFQ on two occasions a month apart, kept a 7d-WR and gave two fasting blood samples at the beginning and end of the study for measuring serum and erythrocyte folate, respectively. Mean folate intakes were similar by repeat FFQ and correlated strongly (r 077 and r 072, P<0.001, for men and women, respectively). All other comparisons were done using the results of the FFQ administered on the first occasion. Men reported similar folate intakes on the FFQ and 7d-WR, but women reported greater intakes on the FFQ compared with the 7d-WR (P<0.05). There was a statistically significant correlation (partial, controlling for gender) between folate intakes reported by FFQ and 7d-WR (r 0.53, P<0.01). Folate intakes estimated by FFQ correlated significantly with serum (r 0.47, P<0.01), but not erythrocyte folate (r 0.25, P>0.05), the strength of the association was greater in men than in women. Validity coefficients estimated using the method of triads were higher for the FFQ than for the 7d-WR when serum folate was used as the biomarker. Overall, these results suggest that this short FFQ is a useful method for assessing folate intake, particularly in men.     

Biomarker and dietary validation of a Canadian food frequency questionnaire to measure eicosapentaenoic and docosahexaenoic acid intakes from whole food, functional food, and nutraceutical sources

BackgroundCanadian dietary sources of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) include marine and non-marine whole foods, functional foods, and nutraceuticals.Objective/designIn the present study, these sources were incorporated into a nutrient-specific, semi-quantitative food frequency questionnaire (FFQ) and the ability to measure the EPA and DHA intakes of Canadian adults was assessed. Specifically, the EPA and DHA intakes estimated by FFQ of 78 men and women, 20 to 60 years of age, were compared with EPA and DHA measurements from 3-day food records and measures of EPA and DHA in fasting whole blood.ResultsMean (±standard deviation) and median intakes of EPA+DHA were 0.34±0.34 and 0.21 g/day by FFQ and 0.47±0.71 and 0.13 g/day by food record, with no significant differences between mean intakes (P=0.93). The FFQ provided higher estimates than the food record at low intakes of EPA and DHA and lower estimates at high intakes based on Bland-Altman plots. The FFQ was moderately correlated with food record (r=0.31 to 0.49) and with blood biomarker measures of EPA and DHA (r=0.31 to 0.51). Agreement analysis revealed that 42% of participants were classified in the same and 77% into same or adjacent quartile when EPA and DHA intake was assessed by food record and by FFQ. Similar quartile agreement was found for EPA and DHA intakes by FFQ with blood biomarker EPA and DHA. The range of the validity coefficients, calculated using the method of triads, was 0.43 to 0.71 for FFQ measurement of EPA+DHA.ConclusionsThe FFQ is an adequate tool for estimating usual EPA and DHA intakes and ranking Canadian adults by their intakes.     

Validation of a Short,Qualitative Food Frequency Questionnaire in French Adults Participating in the MONA LISA-NUT Study 2005-2007

BackgroundFood frequency questionnaires (FFQs) are often used to evaluate individuals' food intakes in epidemiologic studies because of their simplicity and low cost.ObjectiveTo assess the validity of a short (24 items), qualitative FFQ used in the MONA LISA-NUT study.DesignCross-sectional study of a representative sample in three French counties.Participants/settingThe sample included 2,630 participants aged 35 to 65 years from the MONA LISA-NUT study.Main outcome measuresFood consumption was measured with the FFQ and via food records for 3 consecutive days. Plasma fatty acids were measured from a subset of participants.Statistical analyses performedThe FFQ items' validity was assessed by calculating crude and deattenuated Pearson correlation coefficients between frequencies reported by the FFQ and average weights reported by the food records. Furthermore, the validity of some items of the FFQ measuring the consumption of fatty foods was assessed by calculating Pearson correlation coefficients between frequencies of consumption of these foods and dosages of the corresponding plasma fatty acids: fish and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), olive oil and oleic acid, margarine and elaidic acid, and dairy products and pentadecanoic and heptadecanoic acids.ResultsThe mean of the deattenuated Pearson correlation coefficients for all items was 0.46, with values ranging from 0.22 (fried food) to 0.77 (breakfast cereal). The correlation coefficient was ≤0.4 for one third of the 24 items. Moderate correlations were found between fish and EPA/DHA (EPA: r=0.43, 95% CI 0.33 to 0.51; DHA: r=0.39, 95% CI 0.30 to 0.47), but not for other food items.ConclusionsOne third of the 24 items in the short, qualitative FFQ evaluated here were not sufficiently valid. However, for the food groups most commonly studied in the literature, this FFQ had the same degree of validity as other questionnaires designed to classify subjects according to their level of intake.     

Development and validation of a calcium intake questionnaire for postmenopausal women in China

PURPOSE: Develop and evaluate a food frequency questionnaire (FFQ) for assessing calcium intake in Chinese postmenopausal women. METHODS: An interviewer-conducted FFQ that asks respondents about their consumption of 110 calcium-containing foods over the previous week was developed and administered to 21 randomly selected postmenopausal women from Chengdu. This FFQ uses both the traditional weight-estimation method of assessing portion size in China and a new volume-estimation method. Test-retest reliability was assessed by re-administering the questionnaire two weeks later and validity was assessed by comparing the computed daily calcium intake to that obtained by a researcher-conducted 4-day food record. RESULTS: Estimates of calcium intake derived from the volume-estimation method were significantly lower than estimates derived from the traditional weight-estimation method (median calcium intakes = 270 mg/day versus 570 mg/day), but were quite similar to those obtained from the 4-day food record (median calcium intake = 275 mg/day). The test-retest reliability and validity of the volume-estimation method (intraclass correlation coefficient (ICC) = 0.73 and 0.86, respectively) were better than those of the weight-estimation method (ICC = 0.58 and 0.39, respectively). CONCLUSIONS: The reliability and validity of the traditional weight-estimation FFQ method of assessing dietary intake of nutrients in China is poor; this method may significantly overestimate dietary intakes. The proposed volume-estimation FFQ method for assessing calcium intake is a simple, interviewer-conducted method that is both reliable and valid. The calcium intake of postmenopausal women in urban China is much lower than the recommended daily allowance of 800 mg.     

Reproducibility of a food frequency questionnaire: Korea Nurses' Health Study

BACKGROUND/OBJECTIVESThis study aimed to examine the reproducibility of food frequency questionnaires (FFQs) designed for young female nurses in the Korea Nurses'' Health Study.SUBJECTS/METHODSThe reproducibility of web-based, self-administered FFQs was evaluated among 243 Korean female nurses. The first FFQ (FFQ1) was administered from March 2014 to February 2019 and the second FFQ (FFQ2) from November 2019, with a mean interval of 2.8 years between the FFQs (range, 9 months–5.6 years). Pearson and Spearman correlation coefficients (r values) and quartile agreements between FFQ1 and FFQ2 were calculated for intakes of energy, nutrients, and foods.RESULTSPearson correlation coefficients ranged from 0.41 to 0.55 (median r = 0.51) for energy and raw nutrients and from 0.16 to 0.46 (median r = 0.36) for energy-adjusted nutrients. Spearman correlation coefficients ranged from 0.25 to 0.72 (median r = 0.41) for food items. The percentages of women who were classified into the same or adjacent quartile were 77% to 84% (median = 82%) for raw nutrients and 69% to 86% (median = 78%) for foods.CONCLUSIONSThe results indicated that the web-based FFQ used in the Korea Nurses'' Health Study has acceptable reproducibility.     

Relative validity of fruit and vegetable intake estimated by the food frequency questionnaire used in the Danish National Birth Cohort

OBJECTIVE: To validate the fruit and vegetable intake estimated from the Food Frequency Questionnaire (FFQ) used in the Danish National Birth Cohort (DNBC). SUBJECTS AND SETTING: The DNBC is a cohort of 101,042 pregnant women in Denmark, who received a FFQ by mail in gestation week 25. A validation study with 88 participants was made. A seven-day weighed food diary (FD) and three different biomarkers were employed as comparison methods. RESULTS: Significant correlations between FFQ and FD-based estimates were found for fruit (r = 0.66); vegetables (r = 0.32); juice (r = 0.52); fruit and vegetables (F&V) (r = 0.57); and fruit, vegetables, and juice (F&V&J) (r = 0.62). Sensitivities of correct classification by FFQ into the two lowest and the two highest quintiles of F&V&J intake were 58-67% and 50-74%, respectively, and specificities were 71-79% and 65-83%, respectively. F&V&J intake estimated from the FFQ correlated significantly with urinary flavonoids (r = 0.39, p<0.005), plasma beta-carotene (r = 0.21, p<0.05) and erythrocyte folate (r = 0.33, p<0.005); all average biomarker levels increased across increasing quintiles of F&V&J intake. CONCLUSION: Data on F&V&J recorded by FFQ in DNBC can be used in etiological analyses of associations between fruit and vegetable intake and health outcomes, provided that the potential misclassification of dietary exposure is kept in mind.     

Validation of a Semi-Quantitative Food Frequency Questionnaire Measuring Dietary Vitamin K Intake in Elderly People

The study objective was to validate a semi-quantitative food frequency questionnaire (FFQ) specifically designed to measure dietary vitamin K intake. A 50-item FFQ was interviewer-administered and compared with data previously obtained from 5-day food records. Thirty-nine community-dwelling healthy men and women aged 65 to 85 years were recruited from the Montréal metropolitan area. Absolute and relative agreements between methods were assessed. Vitamin K intake measured by the vitamin K FFQ (mean±standard deviation; 222±186 μg/day) was significantly higher than that obtained by food records (135±153 μg/day; P<0.001). Bland-Altman analysis on log₁₀-transformed data indicated that vitamin K intake from vitamin K FFQ was 2.26 times (95% confidence interval: 1.90 to 2.67) higher than food records, limits of agreement ranging from 0.80 to 6.35. However, correlation between methods was strong and highly significant (r=0.83; P<0.001). Cross-classification also showed that 72% of participants were correctly classified into thirds and only 8% were grossly miscategorized. Weighted κ value (κ=0.60) also indicated a good relative agreement. In light of these results, the vitamin K FFQ is a valid tool for ranking individuals according to their vitamin K intake. The poor absolute agreement likely results from the inability for food records to adequately measure the usual intake of episodically consumed foods, particularly those high in vitamin K. The vitamin K FFQ will be useful in large-scale, population-based research on vitamin K and disease as well as in clinical practice, especially that focusing on anticoagulant therapy.