Effect of a controlled high-fat versus low-fat diet on insulin sensitivityand leptin levels in African-American and Caucasian women

African-American women have been shown to be more insulin-resistant than ag e- and weight-matched Caucasian women, but the reasons for this difference are unclear. The purpose of the present study was to determine whether expe rimental manipulation of dietary fat intake has differential effects by rac e on insulin sensitivity (S-1) in 20 African-American and 11 Caucasian wome n. Additionally, leptin levels before and after 3 weeks of an isocaloric hi gh-fat ([HF] 50% fat, 35% carbohydrate, and 15% protein) or low-ist ([LF] 2 0% fat 55% carbohydrate, and 15% protein) diet were compared. African-Ameri can and Caucasian women did not differ significantly in the body mass index (BMI) or percentage body fat at baseline. S-1 (adjusted for BMI) decreased on the HF diet and increased on the LF diet in both races combined relativ e to the baseline control (control, 2.42 +/- 0.22; HF, 2.29 +/- 0.22; LE 2. 75 +/- 0.21 x 10(-4) min(-1)/mu U . mL; main effect of diet, P = .04). Ther e was a 6% decrease in S-1 on the HF diet compared with the control in wome n of both races, while the LF diet increased S-1 by 6% in African-American and 20% in Caucasian women. Leptin levels increased by 14% on the HF versus control diet in African-Americans (35.2 +/- 3.0 v 30.8 +/- 3.0 ng/mL, P < .01), but did not change with diet in Caucasian women. Glucose and insulin administration had no effect on leptin levels. We conclude that a HF diet c onsumed over several weeks reduces S-1 in healthy women of both races; howe ver, the magnitude of increase in S-1 on a LF diet is greater in Caucasian women. The HF diet significantly increased leptin levels in African-America n women, although there were no other influences of diet, insulin, or race on serum leptin. Copyright (C) 1998 by W.B. Saunders Company.