Diet and High-Density Lipoprotein Metabolism
High levels of plasma low-density lipoprotein (LDL) cholesterol constitute a major risk factor for coronary heart disease. Conversely, plasma high-density lipoprotein (HDL) cholesterol and apolipoproteins A-I and A-II, the major protein constituents of HDL, are inversely related to the disease. One approach to lowering LDL and increasing HDL-cholesterol is by dietary means. The recommended diet is low in saturated fat, total fat, and cholesterol. Since the protein content of most diets is relatively constant, a low-fat diet would result in an increase in dietary carbohydrate. The present studies were designed to determine the effect of dietary fatty acids and carbohydrate on lipoprotein metabolism. All studies were performed with normal subjects under metabolic ward conditions with solid-food diets.
The effect of varying polyunsaturated/saturated (P/S) fat ratios on plasma lipids and apo A-I was assessed with an isocaloric diet containing 40% fat, 40% carbohydrate, and 20% protein; the P/S ratio of the diets was 0.4, 1.0, or 2.0. Compared to the P/S = 0.4 diet, mean plasma total cholesterol fell by approximately 6 and 12% on the P/S = 1.0 or P/S = 2.0 diets, respectively; plasma concentrations of LDL-cholesterol, HDL-cholesterol, and apo A-I were also decreased. The mean ± S.E.M. concentration (mg/dl) of HDL-cholesterol was 49.0 ± 5.2 (P/S = 0.4), 44.0 ± 3.8 (P/S = 1.0), and 41.0 ±3.7 (P/S = 2.0). As a result of a reduction in both LDL-and HDL-cholesterol on the polyunsaturatedrich diets, the ratios of HDL-cholesterol to plasma total cholesterol and LDL-to HDL-cholesterol were not significantly changed on the three diets.
The effects of change in dietary carbohydrate on plasma lipids and lipoproteins with a constant P/S ratio of 0.4 were assessed. Seven males and six females received 2 weeks of a high-fat diet (15% carbohydrate, 65% fat, 20% protein) followed by 4 weeks of a high-carbohydrate diet (65% carbohydrate, 15% fat, 20% protein). The high-carbohydrate diet was associated with an increase in fasting plasma triglycerides and insulin. Plasma LDL-and HDL-cholesterol were significantly decreased on the high-carbohydrate diet. However, the ratio of LDL-to HDL-cholesterol was not different on the two diets. The activity of postheparin plasma lipoprotein lipase (LpL) after the high-carbohydrate diet was significantly decreased as compared to the high-fat diet. Changes in LpL activity were significantly positively correlated with HDL-cholesterol and negatively with triglycerides. The changes in lipoproteins with diet were not correlated with the activity of hepatic triglyceride lipase.
In conclusion, the two types of lipid-lowering diets examined were shown to lower LDL-cholesterol. The HDL-cholesterol was lowered on the diet with a P/S ratio of 2.0 and on the high-carbohydrate diet. However, on both diets the ratio of LDL and HDL was unchanged. Thus, both dietary regimens appear to be effective as dietary approaches to preventing coronary heart disease.
KeywordsPlasma Lipid Plasma Total Cholesterol Lipid Research Clinic Isocaloric Diet Clinic Coronary Primary Prevention Trial
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- Lipid Research Clinics Coronary Primary Prevention Trial, 1984, Results J.A.M.A. 251:351–374.Google Scholar
- NHLBI Workshop on The Lipid Research Clinics Coronary Primary Prevention Trial, 1985, Arteriosclerosis 5:397–402.Google Scholar
- NIH Consensus Development Conference, 1985, Lowering blood cholesterol to prevent heart disease, A rteriosclerosis 5:404–412.Google Scholar