Effect of Dietary Stearic Acid on Plasma Cholesterol and Lipoprotein Levels

We studied the metabolic effects of stearic acid (18:0) on plasma lipoprotein levels in 11 subjects during three dietary periods of three weeks each. The three liquid-formula diets, which were used in random order, were high in palmitic acid (16:0), stearic acid, and oleic acid (18:1), respectively. Caloric intakes were the same during the three periods. As compared with the values observed when the subjects were on the high-palmitic-acid diet, plasma total cholesterol decreased by an average of 14 percent during consumption of the high-stearic-acid diet (P<0.005) and by 10 percent during consumption of the high-oleic-acid diet (P<0.02). Low-density lipoprotein cholesterol levels fell by 21 percent in subjects on the high-stearic-acid diet (P<0.005) and by 15 percent in subjects on the high-oleic-acid diet (P<0.005). No significant differences were observed in the plasma levels of triglycerides or high-density lipoprotein cholesterol among the three diets. Measurements of the intestinal absorption of palmitic, stearic, and oleic acids revealed essentially complete absorption of each during the three dietary periods. The oleic acid content of plasma triglycerides and cholesteryl esters increased significantly during the high-steahc-acid period, suggesting that stearic acid is rapidly converted to oleic acid. We conclude that stearic acid appears to be as effective as oleic acid in lowering plasma cholesterol levels when either replaces palmitic acid in the diet. (N Engl J Med 1988; 318:1244–8.) DIETARY saturated fatty acids have been implicated as an important factor in the production of high levels of plasma cholesterol in populations at high risk for coronary heart disease.¹ Although these fatty acids vary in chain length from 4 to 18 carbon atoms, they are generally all considered plasma cholesterol-raising fatty acids. This may not be justified. For example, fatty acids with chain lengths of 4 to 10 carbon atoms have been claimed not to increase the cholesterol level.^{2 3 4} Likewise, stearic acid (18 carbon atoms, no double bonds [18:0]) has been reported not to raise plasma cholesterol levels.^{5 6 7} The principal.