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 b-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 (a-carotene, b-carotene, b-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 a-carotene (0.85) and lycopene (0.62), followed by b-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 b-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.

Evaluation of brief dietary questions to estimate vegetable and fruit consumption - using serum carotenoids and red-cell folate

Objective To evaluate responses to self-administered brief questions regarding consumption of vegetables and fruit by comparison with blood levels of serum carotenoids and red-cell folate.

Design A cross-sectional study in which participants reported their usual intake of fruit and vegetables in servings per day, and serum levels of five carotenoids (α-carotene, β-carotene, β-cryptoxanthin, lutein/zeaxanthin and lycopene) and red-cell folate were measured. Serum carotenoid levels were determined by high-performance liquid chromatography, and red-cell folate by an automated immunoassay system.

Settings and subjects Between October and December 2000, a sample of 1598 adults aged 25 years and over, from six randomly selected urban centres in Queensland, Australia, were examined as part of a national study conducted to determine the prevalence of diabetes and associated cardiovascular risk factors.

Results Statistically significant (P<0.01) associations with vegetable and fruit intake (categorised into groups: ≤1 serving, 2–3 servings and ≥4 servings per day) were observed for α-carotene, β-carotene, β-cryptoxanthin, lutein/zeaxanthin and red-cell folate. The mean level of these carotenoids and of red-cell folate increased with increasing frequency of reported servings of vegetables and fruit, both before and after adjusting for potential confounding factors. A significant association with lycopene was observed only for vegetable intake before adjusting for confounders.

Conclusions These data indicate that brief questions may be a simple and valuable tool for monitoring vegetable and fruit intake in this population.

A dietary guideline adherence score is positively associated with dietary biomarkers but not lipid profile in healthy children

BACKGROUND: Whether dietary indexes are associated with biomarkers of children's dietary intake is unclear. OBJECTIVE: The study aim was to examine the relations between diet quality and selected plasma biomarkers of dietary intake and serum lipid profile. METHODS: The study sample consisted of 130 children aged 4-13 y (mean ± SD: 8.6 ± 2.9 y) derived by using baseline data from an intervention study. The Dietary Guideline Index for Children and Adolescents (DGI-CA) comprises the following 11 components with age-specific criteria: 5 core food groups, whole-grain bread, reduced-fat dairy foods, discretionary foods (nutrient poor; high in saturated fat, salt, and added sugar), healthy fats/oils, water, and diet variety (possible score of 100). A higher score reflects greater compliance with dietary guidelines. Venous blood was collected for measurements of serum lipids, fatty acid composition, plasma carotenoids, lutein, lycopene, and α-tocopherol. Linear regression was used to examine the relation between DGI-CA score (independent variable) and concentrations of biomarkers by using the log-transformed variable (outcome), controlling for confounders. RESULTS: DGI-CA score was positively associated (P < 0.05) with plasma concentrations of lutein (standardized β = 0.17), α-carotene (standardized β = 0.28), β-carotene (standardized β = 0.26), and n-3 (ω-3) fatty acids (standardized β = 0.51) and inversely associated with plasma concentrations of lycopene (standardized β = -0.23) and stearic acid (18:0) (standardized β = -0.22). No association was observed between diet quality and α-tocopherol, n-6 fatty acids, or serum lipid profile (all P > 0.05). CONCLUSION: Diet quality, conceptualized as adherence to national dietary guidelines, is cross-sectionally associated with plasma biomarkers of dietary exposure but not serum lipid profile. This trial was registered with the Australia New Zealand Clinical Trial Registry (www.anztr.org.au) as ACTRN12609000453280.

Testing the interactive effects of carotenoids and polyunsaturated fatty acids on ejaculate traits in the guppy Poecilia reticulata (Pisces: Poeciliidae)

Using the polyandrous livebearing guppy Poecilia reticulata, this study revealed no main effects of carotenoids in the diet on ejaculate traits, but significant main effects of polyunsaturated fatty acids (PUFAs) on sperm viability and weak but significant interacting effects of both nutrients on sperm length. Collectively, these findings not only add evidence that PUFAs are critical determinants of sperm quality, but also provide tentative evidence that for some traits these effects may be moderated by carotenoid intake.