In the first five years of the study analyses were performed on food consumption data collected through semiquantitative food frequency questionnaires at baseline and during follow-up in the Nurses Health Study and Health Professionals Follow-up Study cohorts. Dietary patterns were derived from the food consumption data using factor analysis, cluster analysis, and dietary indexes (based on prevailing dietary recommendations). In addition, using existing datasets from dietary validation studies in sub-samples of the two cohorts, the reproducibility and validity of dietary patterns defined by factor/cluster analysis and dietary indexes were evaluated. Further, using prospectively collected and stored bloods in the NHS (n-32,826) during 1989-1990 and the HPFS (n-18,000) during 1993-1994, the investigators examined whether observed associations between dietary patterns and CHD were explained by (or mediated through) plasma biochemical measurements (including serum lipids, thrombotic factors, antioxidants, fasting insulin, and homocysteine levels) in a nested case-control design; and they assessed prospectively the relationship between dietary patterns and these biomarkers in the control samples.