Construction and evaluation of a self-contained index for assessment of diet quality

Aims: To construct and validate a self-contained index for the evaluation of a health-promoting diet in adults. Methods: Participants (n = 103) were healthy volunteer adults aged 20 to 64 years. A food consumption questionnaire containing 55 questions was formulated and evaluated against seven-day food records. Key questions best reflecting the health-promoting diet, defined in nutrition recommendations, were identified by correlation and ROC analyses in comparison to calculated food and nutrient intakes from the food records. A shorter questionnaire was scored to compile an Index of Diet Quality (IDQ). Results: Based on ROC analyses 18 questions were sufficient to describe the health-promoting diet and comprised the index. IDQ had a sensitivity of 67% and a specificity of 71%. The IDQ score reflected dietary intake, shown as statistically significant correlations between higher IDQ scores and higher intakes of protein (r = 0.35), fibre (r = 0.42), calcium (r = 0.39), iron (r = 0.31), vitamin C (r = 0.31) and a higher ratio of unsaturated to saturated fatty acids (r = 0.23) and a lower intake of saturated fatty acids (r =-0.22) and saccharose (r =-0.25). Conclusions: IDQ reflects dietary intake of key foods and nutrients associated with health and depicts adherence to dietary recommendations. It is applicable in nutritional studies where diet in its entirety is of interest and also in large-scale studies, being fast in execution with analysis free of complex calculations.