Comparative cholesterol lowering properties of vegetable oils: Beyond fatty acids

Objective: Our laboratory has previously reported that the hypolipidemic ef fect of rice bran oil (RBO) is not entirely explained by its fatty acid com position. Although RBO has up to three times more serum cholesterol-raising saturated fatty acids (SATS) than some unsaturated vegetable oils, we hypo thesized that its greater content of the unsaponifiables would compensate f or its high SATS and yield comparable cholesterol-lowering properties to ot her vegetable oils with less SATS. Methods: To study the comparative effects of different unsaturated vegetabl e oils on serum Lipoprotein levels, nine cynomologus monkeys (Macaca fascic ularis) were fed diets, for four weeks, in a Latin square design, containin g rice bran, canola or corn oils (as 20% of energy) in a basal mixture of o ther fats to yield a final dietary fat concentration of 30% of energy. All animals were fed a baseline diet containing 36% of energy as fat with 15% S ATS, 15% monounsaturated fatty acids (MONOS) and 6% polyunsaturated fatty a cids (POLYS). Results: Despite the lower SATS and higher MONOS content of canola oil and the higher POLYS content of corn oil, RBO produced similar reductions in se rum total cholesterol (TC) (-25%) and low density lipoprotein cholesterol ( LDL-C) (-30%). In addition, as compared to the baseline diet, the reduction in serum TC and LDL-C cholesterol with RBO was not accompanied by reductio ns in high density lipoprotein cholesterol (HDL-C) which occurred with the other two dietary oils. Using predictive equations developed from data gath ered from several studies with non-human primates, we noted that the observ ed serum TC and LDL-C lowering capabilities of the RBO diet were in excess of those predicted based on the fatty acid composition of RBO. Conclusions: These studies suggest that non-fatty acid components (unsaponi fiables) of RBO can contribute significantly to its cholesterol-lowering ca pability.