The effects of variations in dietary carbohydrate and fat on various aspects of carbohydrate and lipoprotein metabolism were evaluated in 10 healthy, postmenopausal women. The two diets were isoenergetic, assigned in random fashion, and consisted (as a % of total energy) of 15% protein, 60% carbohydrate, and 25% fat (60%-carbohydrate diet) or 15% protein, 40% carbohydrate, and 45% fat (40%-carbohydrate diet). Fasting plasma triacylglycerol, very-low-density-lipoprotein (VLDL) triacylglycerol, and VLDL-cholesterol concentrations were higher (P < 0.05-0.001) after the 60%-carbohydrate diet, whereas high-density-lipoprotein (HDL) cholesterol was lower (P < 0.05). Plasma insulin and triacylglycerol concentrations were also higher (P < 0.001) from 0800 to 0000 with the 60%-carbohydrate diet than with the 40%-carbohydrate diet. In addition, when vitamin A was given with the noon meal, the ensuing concentrations of retinyl palmitate were also higher after ingestion of the 60%-carbohydrate diet. Resistance to insulin-mediated glucose disposal, quantified at baseline by determining the steady state plasma glucose (SSPG) concentration at the end of a 180-min infusion of somatostatin, insulin, and glucose, correlated with the incremental increases in postprandial concentrations of plasma glucose (r = 0.68, P = 0.06), insulin (r = 0.82, P < 0.02), triacylglycerol (r = 0.77, P < 0.05), and retinyl palmitate (r = 0.68, P = 0.06) and with the Sf > 400 triacylglycerol (r = 0.77, P < 0.05), Sf 20-400 triacylglycerol (r = 0.72, P < 0.05), and Sf > 400 retinyl palmitate (r = 0.75, P < 0.01) lipoprotein fractions. Because all of these changes would increase risk of ischemic heart disease in postmenopausal women, it seems reasonable to question the wisdom of recommending that postmenopausal women consume low-fat, high-carbohydrate diets.