Development and validation of a food frequency index using nutritional biomarkers in a sample of middle-aged and older adults.

An index of diet quality, which examines different aspects of a diet concurrently, may facilitate the identification of poor dietary habits in population sub-groups. The objectives of the present study were to develop a food frequency index (FFI) and to test its associations with nutritional biomarkers and nutrient intake. The study comprised a cross-sectional survey among 444 adults aged 55 years and older in Vienna, Austria, and a sub-sample of 226 subjects who provided fasting blood specimen. Data from a qualitative 28-item food-frequency questionnaire were used to develop the FFI. FFI scores were positively correlated with plasma concentrations of beta-carotene (r = 0.26), beta-cryptoxanthin (r = 0.31), zeaxanthin (r = 0.19), lutein (r = 0.21), phylloquinone (r = 0.19), 25-hydroxyvitamin D (r = 0.20), and serum high-density lipoprotein (HDL)-cholesterol (r = 0.24) and were negatively correlated with the ratio of total : HDL-cholesterol (r = -0.23). Sub-groups with higher FFI scores had, on average, lower intakes of total fat, saturated fat, and dietary cholesterol and higher intakes of total carbohydrates, dietary fibre, and most of the examined micronutrients. The FFI as a measure of diet quality has the ability to discern population sub-groups, with reasonable validity, into low- or high-risk dietary habits.