Reproducibility and validity of dietary patterns assessed with a food-frequency questionnaire.
BACKGROUND: Recently, the analysis of dietary patterns has emerged as a possible approach to examining diet-disease relations. OBJECTIVE: We examined the reproducibility and validity of dietary patterns defined by factor analysis using dietary data collected with a food-frequency questionnaire (FFQ). DESIGN: We enrolled a subsample of men (n = 127) from the Health Professionals Follow-up Study in a diet-validation study in 1986. A 131-item FFQ was administered twice, 1 y apart, and two 1-wk diet records and blood samples were collected during this 1-y interval. RESULTS: Using factor analysis, we identified 2 major eating patterns, which were qualitatively similar across the 2 FFQs and the diet records. The first factor, the prudent dietary pattern, was characterized by a high intake of vegetables, fruit, legumes, whole grains, and fish and other seafood, whereas the second factor, the Western pattern, was characterized by a high intake of processed meat, red meat, butter, high-fat dairy products, eggs, and refined grains. The reliability correlations for the factor scores between the 2 FFQs were 0.70 for the prudent pattern and 0.67 for the Western pattern. The correlations (corrected for week-to-week variation in diet records) between the 2 FFQs and diet records ranged from 0.45 to 0.74 for the 2 patterns. In addition, the correlations between the factor scores and nutrient intakes and plasma concentrations of biomarkers were in the expected direction. CONCLUSIONS: These data indicate reasonable reproducibility and validity of the major dietary patterns defined by factor analysis with data from an FFQ.