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.