Cholesterol-lowering by rice bran and rice bran oil unsaponifiable matter in hamsters

Unsaponfiable matter (U) was prepared from both raw and extrusion stabilized (130°C) rice bran and tested for cholesterol-lowering activity in hamsters by addition to diets containing cellulose, raw rice bran, or stabilized rice bran at either the level found in the rice bran diet (0.4%, 1X) or twice that level (2X). All diets contained 0.3% cholesterol, 10% total dietary fiber, 10.1% fat, and 3% N (same plant-to-animal N ratio). After 21 days, plasma cholesterol was significantly reduced by rice bran diets containing added U compared to the cellulose control diet, while the high density lipoprotein cholesterol-to-low density lipoprotein cholesterol ratio remained unchanged in all treatment groups. Liver cholesterol was significantly reduced by all rice bran-containing diets and with cellulose diets containing 2X added U when compared to the control diet. Rice bran diets plus added U resulted in cholesterol values lower than cellulose diets containing the same level of U. Stabilization of rice bran did not appear to affect the plasma and liver cholesterol responses to the unsaponifiable matter prepared from the extracted oil. There appears to be a dose response to rice bran unsaponifiable matter in plasma and liver cholesterol reductions. After 2 weeks, fecal fat and neutral sterol excretion were significantly greater with all treatment diets compared to the control diet. Fecal fat was negatively correlated with liver as well as plasma cholesterol (r = -0.97, P ≤ 0.0001 and -0.91, P ≤ 0.0006, respectively). Under the conditions of this study, cholesterol-lowering activity of rice bran is present in its unsaponifiable matter in addition to other components. Increased fecal excretion of fat and neutral sterols appears to be a possible mechanism for cholesterol-lowering by rice bran.