The effects of dietary fats on total:HDL cholesterol may differ markedly from their effects on LDL. The effects of fats on these risk markers should not in themselves be considered to reflect changes in risk but should be confirmed by prospective observational studies or clinical trials. By that standard, risk is reduced most effectively when trans fatty acids and saturated fatty acids are replaced with cis unsaturated fatty acids. The effects of carbohydrates and of lauric acid-rich fats on CAD risk remain uncertain.

To calculate the effect of changes in carbohydrate and fatty acid intake on serum lipid and lipoprotein levels, we reviewed 27 controlled trials published between 1970 and 1991 that met specific inclusion criteria. These studies yielded 65 data points, which were analyzed by multiple regression analysis using isocaloric exchanges of saturated (sat), monounsaturated (mono), and poly unsaturated (poly) fatty acids versus carbohydrates (carb) as the independent variables. For high density lipoprotein (HDL) we found the following equation: AHDL cholesterol (mmol/1) =0.012x(carb->sat) + 0.009x (carb-'mono) + 0.007 x(carb-»poly) or, in milligrams per deciliter, 0.47x(carb-»sat) + 034 x (carb-»mono) + 0.28x (carb-*poly). Expressions in parentheses denote the percentage of daily energy intake from carbohydrates that is replaced by saturated, cis-monounsaturated, or polyunsaturated fatty acids. All fatty acids elevated HDL cholesterol when substituted for carbohydrates, but the effect diminished with increasing unsaturation of the fatty acids. For low density lipoprotein (LDL) the equation was ALDL cholesterol (mmol/1) =0.033 x(carb-»sat) -0.006 x (carb->mono) -0.014 x (carb-»pory) or, In milligrams per deciliter, L28x(carb->sat) -0.24x(carb-»mono) -0.55x(carb-»poly). The coefficient for polyunsaturates was significantly different from zero, but that for monounsaturates was not For triglycerides the equation was Atriglycerides (mmol/1) = -0.025 x (carb-»sat) -0.022 x (carb-»-mono) -0.028 x (carb->poly) or, in milligrams per deciliter, -2.22x(carb-»sat) -1.99x(carb->mono) -2.47 x (carb-•poly). Thus, replacement of carbohydrates by fat lowered serum triglycerides independent of the nature of the fat Replacement of saturated by unsaturated fatty acids raised the HDL to LDL cholesterol ratio, whereas replacement by carbohydrates had no effect Thus, under isocaloric, metabolicward conditions the most favorable lipoprotein risk profile for coronary heart disease was achieved if saturated fatty acids were replaced by unsaturated fatty acids, with no decrease in total fat intake. Extrapolation of our data to free-living populations requires more insight into effects of diet on body weight; if high-oil diets promote obesity, then their favorable effects on serum lipids will be lost (Arteriosclerosis and Thrombosis 1992;12:911- gested that the cholesterol-decreasing effect of (n-6) polyunsaturated fatty acids is not limited to LDL but extends to HDL cholesterol. 7 -8 Second, recent studies have failed to show any effect of polyunsaturates on serum total and LDL cholesterol beyond that which could be accounted for by the displacement of saturates from the diet. 910For these reasons, we have screened the literature for well-controlled trials on the effect of dietary fatty acids on serum lipoproteins in humans. Results were combined to derive equations that relate changes in the dietary fatty acid intake to changes in serum HDL, LDL, and total cholesterol and trigh/ceride concentrations. We focused on the most common types of fatty a...

The effect of trans fatty acids on the serum lipoprotein profile is at least as unfavorable as that of the cholesterol-raising saturated fatty acids, because they not only raise LDL cholesterol levels but also lower HDL cholesterol levels.

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Polyunsaturated fatty acids are thought to lower the serum cholesterol level more effectively than monounsaturated fatty acids. It is unclear whether the difference--if any--is due to a lowering of the level of high-density lipoprotein (HDL) or low-density lipoprotein (LDL) cholesterol. We therefore placed 31 women and 27 men on a mixed natural diet rich in saturated fat (19.3 percent of their daily energy intake from saturated fat, 11.5 percent from monounsaturated fat, and 4.6 percent from polyunsaturated fat) for 17 days. For the next 36 days, they received a mixed diet with the same total fat content, but enriched with olive oil and sunflower oil ("monounsaturated-fat diet": 12.9 percent saturated fat, 15.1 percent monounsaturated fat, and 7.9 percent polyunsaturated fat) or with sunflower oil alone ("polyunsaturated-fat diet": 12.6 percent saturated fat, 10.8 percent monounsaturated fat, and 12.7 percent polyunsaturated fat). The serum LDL cholesterol level decreased by 17.9 percent in those on the monounsaturated-fat diet and by 12.9 percent in those on the polyunsaturated-fat diet (95 percent confidence interval for the difference between the effects of the two unsaturated-fat diets, -9.9 percent to 0.0 percent). In men, the HDL cholesterol level fell slightly but not significantly with both diets. In women, the HDL cholesterol level did not change with either. We conclude that a mixed diet rich in monounsaturated fat was as effective as a diet rich in (n-6)polyunsaturated fat in lowering LDL cholesterol. Both diets lowered the level of HDL cholesterol slightly in men but not in women.