A 51-item calcium-focused food frequency questionnaire is a reliable tool to assess dietary calcium intake in postmenopausal women

Given the lack in a valid biomarker to assess dietary calcium intake (dCa_i), reproducible estimation of usual dCa_i is crucial for better understanding of its interaction with health outcomes in specific populations. This study tested the hypothesis that a calcium-focused food frequency questionnaire (FFQ) may be used to estimate dCa_i of women ≥50 years residing in a multicultural environment (Montreal, Canada). One hundred and eight women (age, 63.1 ± 7.7 years; 98% postmenopausal) completed the FFQ twice and 4 nonconsecutive 24-hour recalls (24HRs) over 1 month. Medians of dCa_i were compared by Wilcoxon signed rank test. Reproducibility and relative validity of the FFQ were assessed by Spearman correlation (r_s) and Cohen's weighted kappa (κw). Agreement was further assessed by cross-classification by quartiles, Bland-Altman plot, and sensitivity and specificity analyses. The median (interquartile range) dCa_i estimated by the FFQ and 24HRs were 723 (524-1033) mg/d and 854 (666-1068) mg/d, respectively (P < .001). The FFQs had a strong correlation (r_s = 0.72, P < .001) and moderate agreement (κw = 0.55). The FFQ and 24HRs were moderately correlated (r_s = 0.65, P < .001). Cross-classification showed moderate agreement (κw = 0.42), with 85% of the participants classified into identical or contiguous quartiles and 2.8% into extreme opposite quartiles. According to the Bland-Altman plot, the FFQ underestimated dCa_i with a bias of 99 mg/d (95% limits of agreement, −677 to +480 mg/d). Sensitivity and specificity of identifying intakes <1000 mg/d were 90% and 57%, respectively. This FFQ is a useful tool to discriminate dCa_i <600 and ≥1000 mg/d in postmenopausal women and to rank dCa_i in epidemiological studies.     

Food intake characteristics of hemodialysis patients as obtained by food frequency questionnaire.

OBJECTIVES: Food frequency questionnaires (FFQ) are frequently used in epidemiologic studies of nutrition and food intake. However, the use of FFQs in patients receiving maintenance dialysis has not been extensively studied. We hypothesize that FFQ is a useful tool to assess the food intake differences between patients receiving dialysis and patients not receiving dialysis. DESIGN: Matched exposed-unexposed study with case-controlled design. SETTING: Outpatient dialysis unit affiliated with a tertiary-care community medical center. PATIENTS: From a pool of 102 maintenance hemodialysis (MHD) outpatients in a community dialysis unit, 30 adult MHD outpatients (15 men, 15 women, aged 55.8 +/- 14.6 years) were selected randomly as case subjects. They included 16 African Americans, 8 whites, 4 Hispanics, and 2 Asians. Eleven MHD patients took the multivitamin, Nephrovite (R&D Laboratories, Marina del Rey, CA), regularly. From an archive of 1,610 nondialytic individuals with known FFQ data, 30 control subjects were selected randomly to match the age, race, and sex of the case subjects. INTERVENTION: We used Block's FFQ (version 98), an 8-page self-administered questionnaire that has been widely used in epidemiologic studies. A group of trained research assistants supervised the FFQ administration and interviewed those patients who were not able to answer all of the questions without assistance. Student t test was used to compare group means in form of daily dietary intake, and conditional logistic regression was used to calculate odds ratios for predetermined dichotomizing cutoff levels. MAIN OUTCOME MEASURES: Food intake characteristics of MHD patients as compared with control patients not receiving dialysis. RESULTS: Statistically significant differences between MHD case subjects and nondialytic control subjects were observed between the amounts of daily intake for vitamin C (84 +/- 63 mg/d v 127 +/- 70 mg/d, P = .01), dietary fiber (12 +/- 6 g/d v 18 +/- 11 g/d, P = .02), potassium (2,024 +/- 1,088 mg/d v 2,701 +/- 1,429 mg/d, P = .04), cryptoxanthin (56 +/- 88 microg/d v 140 +/- 118 microg/d, P = .003), and lycopene (2,052 +/- 2,234 microg/d v 4,524 +/- 3,979 microg/d, P = .004). These data indicate that MHD patients had a significantly lower intake of vitamin C, dietary fibers, potassium, and 2 of the carotenoid compounds when compared with individuals not receiving dialysis. Moreover, the daily intake of vitamin B(6) was significantly higher in MHD patients probably because of the high pyridoxine content in Nephrovite. By using the conditional logistic regression analysis, the odds ratios for lower than predetermined cutoff levels in patients receiving dialysis were significant for vitamin C, potassium, and the 2 previously mentioned carotenoids (odds ratio between 3.50 and 7.50, P < .05). CONCLUSIONS: Patients receiving dialysis may consume significantly lower amounts of potassium, vitamin C, and dietary fibers as well as lower amounts of some carotenoids. The FFQ seems to be a useful tool to compare dietary intake of MHD patients with other groups, although it may underestimate the amount of daily protein and energy intake and, hence, may not be an accurate tool for individual assessment of food intake. More studies are required to evaluate the validity of the FFQ in dialysis patients. The lower vitamin C, fiber, and carotenoid intake of MHD patients may be atherogenic. Hence, the hypothesis is proposed that prescribed restrictions in potassium in MHD patients may lead to reduced fruit and vegetable intake, leaving meat and fats as the main source of calories. This may contribute to atherosclerosis and increased cardiovascular morbidity and mortality in these patients. This hypothesis needs to be evaluated in future studies.     

Validation of a food frequency questionnaire for nutritional calcium intake assessment in Italian women

OBJECTIVE: To evaluate a food frequency questionnaire assessing calcium intake in women. DESIGN:: Estimates of calcium intake from the food frequency questionnaire were compared with those from 14 day records from 206 Caucasian women aged 25-75 y in Siena, Italy. SUBJECTS: Subjects were randomly recruited from the residents list of the city of Siena, Italy. Of the 250 initially recruited, 39 did not meet the inclusion criteria or failed to complete the diet record and five outliers were excluded before the statistical analysis on the basis that their diet record was unlikely to represent habitual intake. RESULTS: Mean dietary calcium intakes were 829+/-255 (s.d.) mg/day from the questionnaire and 818+/-260 (s.d.) mg/day from the diet record. The mean difference in intake by the two methods (-11.3+/-116.4 mg/day) did not differ significantly from zero. Specificity in classifying women consuming less than 800 mg/day calcium was 86.6%, and sensibility in classifying women consuming more than 800 mg/day calcium was 89.4%. CONCLUSIONS: The food frequency questionnaire could be used in epidemiological studies to assess calcium intake in young to elderly women. The specificity in identifying low calcium intake subjects makes it useful also as an educational tool in diet counselling and for prescribing calcium supplementation.     

A semiquantitative food frequency questionnaire is a valid indicator of the usual intake of phytoestrogens by south Asian women in the UK relative to multiple 24-h dietary recalls and multiple plasma samples

We investigated the relative validity of an interview-administered FFQ to estimate phytoestrogen intake among South Asian women in the UK. A population-based sample of 108 healthy South Asian women completed random repeated monthly 24-h recalls [with a subsample (n = 58) also providing multiple plasma samples] over a period of 1 y followed by administration of the FFQ. The FFQ produced slightly higher estimates of phytoestrogen intake than the 24-h recalls, but the percentage of women classified into the same +/- 1 quartile by the 2 methods was high for all phytoestrogens (from 81 to 94%) with only a small percentage (<5%) being misclassified into extreme opposite quartiles. Energy-adjusted Spearman correlations coefficients between the estimates obtained by the FFQ and the 24-h recalls were 0.55 for genistein, 0.60 for daidzein, 0.70 for secoisolariciresinol, and 0.63 for matairesinol (all P < 0.001). Spearman correlation coefficients between the FFQ estimates and plasma levels were 0.21 (P = 0.12) for genistein, 0.32 (P = 0.02) for daidzein and 0.10 (P = 0.43) for enterolactone; the corresponding values for the 24-h recalls compared with plasma levels were 0.43 (P < 0.001), 0.40 (P = 0.002), and 0.08 (P = 0.50), respectively. The method of triads was used to estimate the validity coefficients (VCs) between the estimates provided by each assessment method and "true intake." The FFQ had the highest VC for lignans (0.91 vs. 0.73 for 24-h recalls and 0.11 for plasma samples) and satisfactory VCs for both genistein (0.46 vs. 0.95 and 0.45, respectively) and daidzein (0.67 vs. 0.83 and 0.45, respectively). This FFQ is thus a relatively valid tool with which to estimate phytoestrogen intake among South Asian women in the UK.     

Food predictors of plasma beta-carotene and alpha-tocopherol: validation of a food frequency questionnaire

Nutrient intakes from a food frequency questionnaire are usually calculated as the product of frequency of intake and nutrient composition of the food, summed over the food items. This involves assumptions about the accuracy of recording, food composition data, stability during storage and preparation, and bioavailability. This usual method of calculation was compared with one using empirical weights derived by multivariate linear regression. Food intakes reported on a food frequency questionnaire by Boston, Massachusetts, area subjects in 1982-1985 were used to predict plasma levels of beta-carotene among 370 male and female nonsmokers and plasma levels of alpha-tocopherol among 339 male and female nonusers of vitamin supplements. Nutrient intake computed using empirical weights yielded a significant correlation with plasma beta-carotene (r = 0.43, p = 0.0001), similar to the correlation using nutrient intake calculated from food composition tables (r = 0.38, p = 0.0001). However, the use of empirical weights significantly improved the correlation of vitamin E intake with plasma alpha-tocopherol levels (r = 0.32, p = 0.0001), compared with the weak correlation obtained using the food composition table method to calculate intake (r = 0.16). The results support the validity of published food composition data used to compute carotenoid intake and illustrate the potential utility of empirically derived weights for foods to predict plasma levels of some nutrients.     

Comparison of a food frequency questionnaire with an online dietary assessment tool for assessing preschool children’s dietary intake

Background: It is important to assess the dietary habits of children as they progress from early childhood to adolescence. However, there are few validated tools available to assess the diet of this group of children. The present study aimed to investigate the relative validity of a food frequency questionnaire (FFQ) developed for use in a biennial longitudinal study. Methods: The parents of 216 Belgian–Flemish preschool children completed a FFQ (including questions on 77 food groups) and an online dietary assessment tool for three nonconsecutive days on their child’s diet. Intakes of energy, macronutrients, fibre, calcium and 20 food groups recorded by both methods were compared using Spearman’s correlations, Wilcoxon’s signed rank test and Bland and Altman analyses. Results: At the group level, good agreement was found for energy, fat and protein intake, an overestimation was found for carbohydrates (5.6%) and fibre (13.3%), and an underestimation was found for calcium (9%). For the food groups, overestimation as well as underestimation and good agreement were found, although overestimation was most common. Good agreement was found in ranking the children’s fruit (r = 0.53), beverages (r = 0.58–0.76), soup (r = 0.51), breakfast cereals (r = 0.55) and calcium (r = 0.59) intake according to both methods. Conclusion: The results obtained revealed that the FFQ was a useful alternative for estimating energy and macronutrient intake at a group level; however, when used to estimate fibre and calcium intake, respectively, over‐ and underestimation need to be considered. The short reference period (3 days) may have compromised agreement in ranking and agreement at the individual level.     

Comparison of a food frequency questionnaire using reported vs standard portion sizes for classifying individuals according to nutrient intake

Individual intakes of retinol, carotene, vitamin C, and folacin calculated from a food frequency questionnaire using reported portion size were compared with intakes calculated using standard portion size information. Data from a case-control study to determine the association of nutrient intake and risk of cervical dysplasia were supplemented by standard portion size information from the US Department of Agriculture and reanalyzed. Significant mean differences were found between intake calculated from reported portion size data and that calculated from standard portion size data for all nutrients. Correlation of nutrient intakes obtained by the two methods of data collection ranged from .73 to .92. Calculation of the rho statistic, measuring the consistency of classification of participants into groups of high, medium, and low nutrient intake, led to values ranging from .55 to .71, indicating some misclassification of study participants. To determine the effect misclassification had on the study outcome, odds ratios were calculated using nutrient amounts obtained from both methods of collecting portion size data. Results indicate that replacing reported portion size data with standard portion size data may lead to conflicting outcomes for specific nutrients in research concerning the relationship between diet and disease.     

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.     

Evaluation of a semi-quantitative food frequency questionnaire to estimate iodine intake

OBJECTIVE: To evaluate a food frequency questionnaire (FFQ) used to assess the dietary intake of iodine. DESIGN: The iodine intake determined by the FFQ was compared with 4-day dietary records and with iodine excretion in 24 h urine samples in a subgroup of participants in a cross-sectional study of iodine intake and thyroid diseases in Denmark. Furthermore, the intake of fish determined from the FFQ was compared with the intake of fish from a simple record kept for 3 months. SUBJECTS: Women aged 25-30 y and 60-65 y. RESULTS: Median iodine intake was similar when determined from the FFQ and from dietary records and the correlation between these measures was 0.52 (P < 0.001). Iodine intake was higher than iodine excretion (P < 0.001). The cross-check questions in the FFQ (for example the question 'How often did you get any kind of fish?') underestimated the intake. In contrast, the intake of a specific fish tended to be overestimated by the FFQ when compared with the 3 month record of fish intake. CONCLUSION: The FFQ can be used to classify subjects into low and high iodine intake groups, but the level of iodine tends to be overestimated.     

Validation of a food frequency questionnaire for assessment of calcium and bone-related nutrient intake in rural populations

OBJECTIVE: To assess the ability of a semiquantitative food frequency questionnaire (FFQ) to measure calcium and bone-related nutrient intakes in a rural South Dakota population. DESIGN: Intake estimates from FFQ were compared with four 24-hour recalls obtained quarterly during the preceding year. SUBJECTS: Convenience sample of 100 participants of the South Dakota Rural Bone Health Study were recruited, with 81 completing the FFQ. MAIN OUTCOME MEASURES: Calcium and bone-related nutrient intakes were expressed as milligrams per day, milligrams per 1,000 kcal, or quartiles. STATISTICAL ANALYSES PERFORMED: Intakes by FFQ and 24-hour recalls were compared using paired t test and quartiles were formed to examine cross-classification. RESULTS: Calcium intakes from FFQ and recalls were 1,287 and 1,141 mg/day (P=0.01), but calcium per 1,000 kcal did not differ. Calcium intake by FFQ correlated with intake by recall when expressed as milligrams per day (r=0.49, P<0.001) or milligrams per 1,000 kcal (r=0.59, P<0.001). Bland-Altman graphs indicated fairly good agreement between methods. Seventy-eight percent of subjects fell into the same or within one quartile category when calcium intake was expressed as milligrams per day and 83% when expressed as milligrams per 1,000 kcal. Gross misclassification occurred in 0% to 4% of the nutrients. CONCLUSIONS: Although FFQ may not be a valid indicator of an individual's intake, it does adequately classify rural populations into quartiles of calcium and bone-related nutrient intakes, making it a useful tool for assessing dietary calcium and bone related intake in rural populations.     

Validation of a food-frequency questionnaire assessment of carotenoid and vitamin E intake using weighed food records and plasma biomarkers: the method of triads model

BACKGROUND: Reliability or validity studies are important for the evaluation of measurement error in dietary assessment methods. An approach to validation known as the method of triads uses triangulation techniques to calculate the validity coefficient of a food-frequency questionnaire (FFQ). OBJECTIVE: To assess the validity of an FFQ estimates of carotenoid and vitamin E intake against serum biomarker measurements and weighed food records (WFRs), by applying the method of triads. DESIGN: The study population was a sub-sample of adult participants in a randomised controlled trial of beta-carotene and sunscreen in the prevention of skin cancer. Dietary intake was assessed by a self-administered FFQ and a WFR. Nonfasting blood samples were collected and plasma analysed for five carotenoids (alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein, lycopene) and vitamin E. Correlation coefficients were calculated between each of the dietary methods and the validity coefficient was calculated using the method of triads. The 95% confidence intervals for the validity coefficients were estimated using bootstrap sampling. RESULTS: The validity coefficients of the FFQ were highest for alpha-carotene (0.85) and lycopene (0.62), followed by beta-carotene (0.55) and total carotenoids (0.55), while the lowest validity coefficient was for lutein (0.19). The method of triads could not be used for beta-cryptoxanthin and vitamin E, as one of the three underlying correlations was negative. CONCLUSIONS: Results were similar to other studies of validity using biomarkers and the method of triads. For many dietary factors, the upper limit of the validity coefficients was less than 0.5 and therefore only strong relationships between dietary exposure and disease will be detected.     

Production and validation of a food frequency questionnaire to estimate dietary fat intake

A quantitative 92-item food frequency questionnaire (FFQ), using photographs to estimate portion size, was developed from a 180-item FFQ and validated by comparison with weighed dietary records of 80 adults. The main aim of the FFQ was to classify subjects according to their fat intake as a percentage of total energy intake. Correlation coefficients and classification of individuals into thirds for fat (g), percentage energy from fat and total energy, showed good agreement between the FFQ and the diet record. There was significant difference in the mean percentage energy from fat but not in grams of fat or total energy intake estimated by the two methods. Intra-class correlation coefficients indicated a significant relationship between an individuals>> percentage energy from fat estimated by the FFQ and diet records. These results suggest that the FFQ was suitable for classifying individuals into groups based on their percentage energy from fat and for estimating the actual average fat and energy intake of groups, and that the FFQ may be useful for estimating the percentage energy from fat for an individual.     

Comparison of plasma biomarkers with dietary assessment methods for fruit and vegetable intake

OBJECTIVE: To assess the variability and validity of plasma-based biomarkers of antioxidant vitamin, and fruit and vegetable intake. SETTING: Leeds, Wakefield, Huddersfield and Bradford, England. SUBJECTS: A total of 54 free-living, nonsmoking women recruited from participants of the UK Women's Cohort Study (UKWCS). METHODS: Two fasting blood samples were taken at two time points, 18 months apart. A 4-day food diary was completed prior to the first blood sample and a 24-h recall was conducted at the time of the second blood collection. All blood samples were analysed for ascorbic acid and four carotenoids. Associations between antioxidant vitamin intake from all food sources and supplements, as well as fruit and vegetable intake, and plasma levels of the antioxidant vitamins were assessed. RESULTS: Using the 4-day diary, positive associations were found between micronutrient intake from all food sources and plasma concentrations of ascorbic acid (P<0.01) and beta-carotene (P<0.01). No associations were seen between plasma micronutrient levels and specifically fruit and vegetable intakes. In general, associations between plasma levels and intakes assessed by the 24-h recall were less marked than those based on the 4-day diary. CONCLUSIONS: Plasma ascorbic acid and beta-carotene are good indicators of previous vitamin C and beta-carotene intake, from all food sources. However, caution is required in extrapolating these results to include individual food groups, rich in these vitamins. The results imply that the practice of using plasma biomarkers simply as a proxy measure of dietary intake is not valid and emphasise that plasma biomarkers are not simply a reflection of dietary intake, but also of a number of physiological processes. Biomarkers in nutrition epidemiological studies are however useful to measure nutrient status at the tissue level.     

Development and validation of a food frequency questionnaire to estimate the intake of genistein in Malaysia

Abstract

Objective: To develop and validate a food frequency questionnaire (FFQ) to estimate the genistein intake in a Malaysian population of pregnant women. Method: A single 24-h dietary recall was obtained from 40 male and female volunteers. A FFQ of commonly consumed genistein-rich foods was developed from these recalls, and a database of the genistein content of foods found in Malaysia was set up. The FFQ was validated against 7-d food diary (FD) kept by 46 pregnant women and against non-fasting serum samples obtained from 64 pregnant women. Reproducibility was assessed by comparing the responses on two FFQs administered approximately 1 month apart. Results: The Pearson correlation coefficient between FFQ1 and FD was 0.724 and that between FFQ2 and FD was 0.807. Classification into the same or adjacent quintiles was 78% for FFQ1 versus FD and 88% for FFQ2 versus FD. A significant dose -- response relation was found between FFQ-estimated genistein intake and serum levels. Conclusion: The FFQ developed is a reliable, valid tool for categorising people by level of genistein intake.     

Validation of a questionnaire assessing food frequency and nutritional intake in Greek adolescents

The aim of the study was to develop and validate a specific semi-quantitative food frequency questionnaire to assess nutritional intake of Greek adolescents. The sample of the study consisted of 250 pupils (15.3 +/- 0.7 years), who completed the Youth Adolescent Food Frequency Questionnaire enriched with 22 Greek foods and recipes to include ethnic and racial diversity. A 3-day weighed food recall was used as the criterion to test the validity of the questionnaire. The analysis of correlation revealed significant correlations between the two methods for almost all variables. The Pearson's coefficients ranged from 0.83 for energy intake to 0.34 for folate intake. Non-significant correlations were found for selenium and vitamin D intakes. The findings of the study provide evidence for the validity of the scale and its utility in assessing nutritional intake of Greek adolescents.