Concern about high-carbohydrate (CHO) diets is based on evidence that they increase fasting plasma triglyceride concentrations, causing high degrees of postprandial lipemia. Day-long elevations in triglyceride-rich lipoproteins may be problematic because of the atherogenic nature of these particles. Alternatively, it has been argued that the lower fat content of high-CHO diets leads to lower postprandial concentrations of triglyceride-rich lipoproteins. This argument is based on the postulate that the magnitude of postprandial lipemia is a direct function of dietary fat content. If the degree of postprandial lipemia is confirmed as a coronary heart disease risk factor, diet modification to reduce fasting and postprandial lipemia is reasonable. Abbasi and associates studied the effects of a CHO–enriched diet on fasting lipid and lipoprotein concentrations.
A group of eight healthy adult volunteers who were free of metabolic disorders or other major medical problems were enrolled in the study. Physical examinations, blood count, urinalysis and baseline lipid values were obtained for all volunteers. The group of four men and four women was randomized to one of two 14-day eucaloric diets, varying in composition of CHO and fat. Saturated fat intake was limited to less than 10 percent in both groups. Dietary fiber was higher in the high-CHO diet. After 14 days on the specialized diets, all volunteers were admitted to the clinical research center for serial blood measurements, including plasma triglyceride, cholesterol and low- (LDL) and high-density (HDL) lipoprotein levels. After a 14-day washout period, the volunteers were randomized to the other diet following the same protocol.
Volunteers on the high-CHO diet had significantly higher plasma triglyceride levels and lower HDL concentrations during fasting and postprandial states. Plasma cholesterol and LDL cholesterol levels were the same in both diets. While on the lower CHO, higher fat (monounsaturated and/or polyunsaturated) diet, volunteers' total and LDL cholesterol levels did not increase as might have been anticipated because of the ingestion of more fat.
The authors conclude that substituting a CHO–enriched diet for one high in saturated fat leads to higher plasma triglyceride and lower HDL concentrations, associated with day-long increases in circulating triglycerides. All of these changes are related to enhanced atherogenesis. These results suggest that efforts to lower LDL cholesterol do not depend on substitution of CHO for saturated fat but can be equally effective when saturated fat is replaced with monounsaturated and/or polyunsaturated fat.