In this study we compared the effects of variations in
dietary fat and
carbohydrate (CHO) content on concentrations of
triglyceride-rich
lipoproteins in 8, healthy, nondiabetic volunteers. The diets contained, as a percentage of total calories, either 60% CHO, 25% fat, and 15%
protein, or 40% CHO, 45% fat, and 15%
protein. They were consumed in random order for 2 weeks, with a 2-week washout period in between. Measurements were obtained at the end of each dietary period of plasma
triglyceride,
cholesterol,
low-density lipoprotein (
LDL) cholesterol,
high-density lipoprotein (
HDL) cholesterol, remnant
lipoprotein (RLP)
cholesterol, and RLP
triglyceride concentrations, both after an overnight fast and throughout an 8-hour period (8 A.M. to 4 P.M.) in response to breakfast and lunch. The 60% CHO diet resulted in higher (mean +/- SEM) fasting plasma
triglycerides (206 +/- 50 vs 113 +/- 19 mg/dl, p = 0.03), RLP
cholesterol (15 +/- 6 vs 6 +/- 1 mg/dl, p = 0.005), RLP
triglyceride (56 +/- 25 vs 16 +/- 3 mg/dl, p = 0.003), and lower
HDL cholesterol (39 +/- 3 vs 44 +/- 3 mg/dl, p = 0.003) concentrations, without any change in
LDL cholesterol concentration. Furthermore, the changes in plasma
triglyceride, RLP
cholesterol, and RLP
triglyceride persisted throughout the day in response to breakfast and lunch. These results indicate that the effects of lowfat diets on
lipoprotein metabolism are not limited to higher fasting plasma
triglyceride and lower
HDL cholesterol concentrations, but also include a persistent elevation in RLPs. Given the atherogenic potential of these changes in
lipoprotein metabolism, it seems appropriate to question the wisdom of recommending that all Americans should replace dietary saturated fat with CHO.