Validation of a quantitative FFQ for the Barbados National Cancer Study

Abstract

Objective: To assess the validity of a 148-item quantitative FFQ (QFFQ) that was developed for the Barbados National Cancer Study (BNCS) to determine dietary intake over 12 months and examine the dietary risk factors. Design: A cross-sectional validation study of the QFFQ against 4 d food diaries. Spearman's rank correlations (r), intra-class correlation coefficients (ICC) and weighted k were computed as measures of concordance, adjusting for daily variations in the food diaries. Cross-classification tables and Bland-Altman plots were created for further assessment. Setting: BNCS is a case-control study of environmental risk factors for breast and prostate cancer in a predominantly African-origin population in Barbados. Subjects: Fifty-four individuals (21 years and older) were recruited among controls in the BNCS who were frequency-matched on sex and age group to breast and prostate cancer cases. Results: Similar mean daily energy intake was derived from the food diary (8201 kJ (1960 kcal)) and QFFQ (7774 kJ (1858 kcal)). Rho for energy and macronutrients ranged from 0?66 (energy) to 0?17 (dietary fibre). The percentage of energy from carbohydrates and protein showed the highest and lowest ICC among macronutrients (0?63 and 0?27, respectively). The highest weighted k was observed for energy (0?45). When the nutrient intake was divided into quartiles, approximately 34 % of the observations were in the same quartile. Conclusions: This investigation supports the validity of the QFFQ as a method for assessing long-term dietary intake except for dietary fibre, folate, vitamins A, E and B 12 . The instrument will be a useful tool in the analysis of diet-cancer associations in the BNCS. Keywords Quantitative FFQ Food diary Validity Barbados National Cancer StudyThe Barbados National Cancer Study (BNCS) is a populationbased case-control study designed to examine the genetic and environmental risk factors for breast and prostate cancer in a predominantly African-origin population. The importance of nutrition-related factors and growing interest in the role of nutrient-gene interactions in cancer aetiology necessitates the development of a valid method for assessing long-term dietary intake. Studies on the association between diet and cancer have not been performed in Barbados, West Indies, likely due, in part, to the lack of a validated method to assess long-term dietary intake.To fill this gap, a 148-item quantitative FFQ (QFFQ) was developed to determine dietary intake and to examine hypotheses related to diet and its interaction with genes and cancer in African-Barbadians (1) . QFFQ is commonly used in large-scale epidemiological studies and provides a feasible approach to assess the usual long-term dietary intake of a population (2) . Only valid instruments provide correct estimates of diet and diet-cancer associations. Although a gold standard to validate QFFQ currently does not exist, its validity is evaluated by comparing the results of these instruments to those using other dietary assessment methods or ...

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