OBJECTIVE: The Women's Health Trial: Feasibility Study in Minority Populations (WHT: FSMP) documented that a low-fat diet was associated with a reduced fat intake in older women of diverse ethnic backgrounds. The purpose of the current study was to examine the effect of the low-fat diet on anthropometric and biochemical variables. DESIGN: Randomized clinical trial in 2,208 postmenopausal women, 50 to 79 years of age. RESULTS: The decrease in fat intake correlated directly with a decrease in body weight (r=.22, P<.001). After 6 months, the intervention group had an average weight loss of 1.8 kg. Body mass index decreased 0.7 kg/m2. Waist circumference decreased 1.8 cm. All of these changes were statistically significant, compared to changes in the control group (P<.01). Changes in systolic (-3.1 mm Hg) and diastolic (-1.1 mm Hg) blood pressures (BP) occurred in the intervention group. The decrease in systolic BP reached statistical significance (P=.02), relative to the control group. Decreases in plasma glucose were small (-0.2 mmol/L) in the intervention group, although there was a trend for difference from the control group (P=.11). Decreases in serum insulin levels were small (-0.5 microIU/mL) in the intervention group, although there was, again, a trend for difference from the control group. CONCLUSIONS: In older White, Black, and Hispanic women, a long-term low-fat dietary intervention was accompanied by modest, but statistically significant, decreases in body weight and anthropometric indices, without any particular attempt being made to reduce calories. Changes in glucose and insulin were small. The long-term biological significance of the glucose and insulin changes is unknown.