Objective: To compare different statistical methods for assessing the relative validity of a self-administered, 150-item, semi-quantitative food-frequency questionnaire (FFQ) with 4-day weighed diet records (WR). Design: Subjects completed the Scottish Collaborative Group FFQ and carried out a 4-day WR. Relative agreement between the FFQ and WR for energy-adjusted nutrient intakes was assessed by Pearson and Spearman rank correlation coefficients, the percentages of subjects classified into the same and opposite thirds of intake, and Cohen's weighted kappa. Subjects: Forty-one men, mean age 36 (range 21-56) years, and 40 women, mean age 33 (range 19-58) years, recruited from different locations in Aberdeen, Scotland. Results: Spearman correlation coefficients tended to be lower than Pearson correlation coefficients, and were above 0.5 for 10 of the 27 nutrients in men and 17 of the 27 nutrients in women. For nutrients with Spearman correlation coefficients above 0.5, the percentage of subjects correctly classified into thirds ranged from 39 to 78%, and weighted kappa values ranged from 0.23 to 0.66. Conclusions: Both Spearman correlation coefficients and weighted kappa values are useful in assessing the relative validity of estimates of nutrient intake by FFQs. Spearman correlation coefficients above 0.5, more than 50% of subjects correctly classified and less than 10% of subjects grossly misclassified into thirds, and weighted kappa values above 0.4 are recommended for nutrients of interest in epidemiological studies. Keywords Correlation coefficientsKappa statistic Food-frequency questionnaire Relative validity Weighed diet records Epidemiological methods Dietary assessmentThe semi-quantitative food-frequency questionnaire (FFQ) is the primary dietary assessment method used in epidemiological studies 1. Results from such studies can be interpreted with greater confidence if the questionnaire has a quantified validity; i.e. the ability of the questionnaire to measure what it is intended to measure. To assess the true validity of an FFQ would require measuring with high accuracy the usual self-selected diet of freeliving individuals over several months, which is not feasible. Therefore, researchers assess relative validity by comparing the FFQ with an alternative dietary assessment method with its own limitations.In epidemiological studies, the odds ratio or relative risk of disease in relation to nutrient intake is the most common measure of association presented. Consequently, FFQs must be able to rank individuals along the distribution of intake, so that individuals with low intakes can be separated from those with high intakes. Therefore, obtaining absolute nutrient intakes is not necessary. As long as FFQs can rank individuals, relative risk estimates will be accurate 2 . The usual method of assessing agreement in ranking between an FFQ and a reference method is to calculate Pearson correlation coefficients for log e -transformed data or Spearman rank correlation coefficients for data that are not n...

The Survey of Sugar Intake among Children in Scotland was carried out in May to September 2006. The present study aimed to identify dietary patterns in school-aged children from the survey and investigate associations with socio-economic factors, obesity and physical activity. Habitual diet was assessed using the Scottish Collaborative Group FFQ. Height and weight were measured by trained fieldworkers. A total of 1233 FFQ were available for analysis. Dietary patterns were identified by age (5 -11 and 12-17 years) and sex using principal components analysis. Associations between factor scores and socio-economic status, education level of the main food provider, physical activity levels and BMI category (based on UK 1990 charts) were examined. Three dietary patterns were identified in each age and sex group. 'Healthier' patterns loading highly for fruit and vegetables were significantly associated with higher socio-economic status and higher education levels of the main food provider whereas more 'unhealthy' patterns ('snacks' and 'puddings') were associated with lower socio-economic status and lower education levels of the main food provider. There was no consistent association between dietary patterns and BMI group or time spent in physical activity. However, inactivity (screen time) was inversely associated with 'healthier' patterns in all age and sex groups and positively associated with 'puddings' and 'snacks' in girls aged 5 -11 years. Clear dietary patterns can be identified in school-age children in Scotland, which are consistently related to socio-economic factors and inactivity. This has implications for targeting health promotion at subgroups in terms of lifestyle changes required.Dietary patterns: Principal components analysis: Children: Inactivity: Overweight Traditionally research on diet and health has focused on intakes of individual nutrients and/or foods or food groups. However, diet is complex and intake of individual nutrients or foods is not independent of intakes of other nutrients or foods. More recently a number of statistical methods have been used to identify patterns of dietary behaviour. The most popular of these is principal components analysis (PCA) (1) , a data-driven method which identifies foods that are frequently eaten together by aggregating items based on the degree to which the amounts consumed are correlated with one another. The aim of PCA is to identify groups of food that account for the largest amount of variation in overall diet between individuals. This method has been mainly used in studies of diet in adult populations but has also been used previously to explore dietary patterns in British, Spanish, Australian, Korean and Finnish children (2 -11) .In 2005, the Food Standards Agency Scotland commissioned the 'Survey of Sugar Intake among Children in Scotland' (12) to provide information on the diet of children in Scotland, with a particular focus on the intake of non-milk extrinsic sugars and sugar-containing foods. The aims of the present study were to identify diet...

There is wide interindividual variation in the lipid and lipoprotein responses to dietary change, and the existence of consistent hypo- and hyperresponders supports the hypothesis that responsiveness is related to genetic variation. Many studies have investigated the possibility that the heterogeneity in responsiveness to changes in dietary fat, cholesterol, and fiber intake is explained by variation in genes whose products affect lipoprotein metabolism, eg, apolipoproteins, enzymes, and receptors. A systematic review of the literature was carried out to investigate the effect of genetic variation on the lipid response to dietary intervention. A search strategy for the MEDLINE database retrieved 2540 articles from 1966 to February 2002. This strategy was adapted and performed on the EMBASE database, which retrieved 2473 articles from 1980 to week 9, 2002. Reference lists from relevant journal articles were also checked. This is the first systematic review of the literature, and it summarizes results available from 74 relevant articles. There is evidence to suggest that variation in the genes for apolipoprotein (apo) A-I, apo A-IV, apo B, and apo E contributes to the heterogeneity in the lipid response to dietary intervention. However, the effects of genetic variation are not consistently seen and are sometimes conflicting. Future studies need to have much larger sample sizes based on power calculations and carefully controlled dietary interventions and should investigate the effects of polymorphisms in multiple genes instead of the effects of polymorphisms in single genes.

These data indicate that a relatively high daily consumption of tomato-based products (equivalent to 32-50 mg lycopene/d) or lycopene supplements (10 mg/d) is ineffective at reducing conventional CVD risk markers in moderately overweight, healthy, middle-aged individuals. This trial was registered at isrctn.org as ISRCTN34203810.

Cytochrome P-450 (CYP) 1A1 plays a key role in phase I metabolism of polycyclic aromatic hydrocarbons and in estrogen metabolism. It is expressed predominantly in extrahepatic tissues, including the breast. Four CYP1A1 gene polymorphisms (3801T --> C, Ile462Val, 3205T --> C, and Thr461Asp) have been studied in relation to breast cancer. The 3801C variant is more common than the Val variant. Both variants occur more frequently in Asians than in White populations. The 3205T --> C polymorphism has been observed in African Americans only. Little data are available on the geographic/ethnic distribution of the Thr461Asp polymorphism. The functional significance of the polymorphisms is unclear. In 17 studies, no consistent association between breast cancer and CYP1A1 genotype was found. Meta-analysis found no significant risk for the genotypes 1) 3801C/C (relative risk (RR) = 0.97, 95% confidence interval (CI): 0.52, 1.80) or 3801T/C (RR = 0.91, 95% CI: 0.70, 1.19) versus 3801T/T, 2) Val/Val (RR = 1.04, 95% CI: 0.63, 1.74) or Ile/Val (RR = 0.92, 95% CI: 0.76, 1.10) versus Ile/Ile, or 3) Asp/Asp (RR = 0.95, 95% CI: 0.20, 4.49) or Thr/Asp (RR = 1.12, 95% CI: 0.87, 1.43) versus Thr/Thr. Future studies should explore possible interactions between CYP1A1 and sources of polycyclic aromatic hydrocarbons, markers of estrogen exposure, other lifestyle factors influencing hormonal levels, and other genes involved in polycyclic aromatic hydrocarbon metabolism or hormonal biosynthesis.