EFFECT OF A HIGH-CARBOHYDRATE, LOW-SATURATED-FAT DIET ON APOLIPOPROTEIN-B AND TRIGLYCERIDE-METABOLISM IN PIMA-INDIANS

The mechanisms by which high-carbohydrate, low-saturated-fat diets lower LDL cholesterol (LDLC) concentrations are unknown. In this study, kinetics of VLDL, intermediate density lipoprotein (IDL), and LDL apoprotein B and VLDL triglyceride were determined in seven nondiabetic (ND) and seven non-insulin-dependent diabetic (NIDDM) Pima Indian subjects on high-fat and high-carbohydrate (HICHO) diets. Metabolic changes were similar in ND and NIDDM. On the HICHO diet, LDLC decreased (131±8 vs. 110±7 mg/dl, P < 0.0001) in all subjects. Mean fasting and 24-h triglyceride (TG) concentrations were unchanged, as were mean production rates and fractional clearance rates (FCR) of VLDL apoB and VLDL TG. The mean VLDL apoB pool size (303±20 vs. 371±38 mg, P = 0.01) increased owing to a decrease in the mean transport rate (10.7±1.1 vs. 8.4±0.9 mg/kg fat-free mass (ffm) per day, P < 0.0001) and the mean rate constant (2.3±0.2 vs. 1.5±0.2, P < 0.001) for the VLDL apoB to IDL apoB conversion pathway. The mean transport rate of VLDL apoB to LDL apoB via IDL (10.2±0.9 vs. 8.0±0.8 mg/kg ffm per day, P < 0.001) decreased. Mean LDL apoB concentrations decreased (70±5 vs. 61±5 mg/dl, P < 0.001) on the HICHO diet. Means for total LDL apoB transport rate, LDL apoB FCR, and LDLC/apoB ratios were unchanged. In summary, the HICHO diet decreased the activity of mechanisms that convert VLDL to LDL, which contributed to the decrease in LDLC in all subjects. There was also evidence in some subjects for increased activity of LDL apoB clearance mechanisms, and a decrease in the LDLC to apoB ratio.