Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/1996
Publication Date: N/A
Interpretive Summary: High cholesterol is a risk factor for heart disease, and the control of cholesterol by diet is preferable to the use of drugs. Many experiments have shown that soluble fiber, found in oats, barley, and some other foods, will lower cholesterol if taken regularly in substantial amounts. We have shown that compounds related to vitamin E, also found in oats and barley, will also lower cholesterol. We designed an experiment using chickens as a model to see the effects of soluble fiber and the vitamin E compounds together. We found that the diet containing both soluble fiber from oat bran and the vitamin E compound (from palm oil) lowered cholesterol more than diets with either component alone. The barley-containing diets did not have enough of the vitamin E compound to cause a greater effect than the soluble fiber alone. We did find that the soluble fiber of barley affected the activities of certain enzymes of cholesterol metabolism. This will help us understand how soluble fiber exerts its effect, and allow us to design more effective foods for cholesterol control. If the results are applicable to humans, they may find the combination of soluble fiber from oat or barley and vitamin E compounds preferable to large quantities of oat bran or similar foods.
Technical Abstract: Effects of cereal grain diets on serum lipids have been attributed to soluble fiber and to tocotrienols. Chickens were fed diets containing oat bran or barley, enriched or depleted in beta-glucan and/or tocotrienols. Serum cholesterol and triglycerides and enzymes of cholesterol metabolism were measured. Oat bran-containing diets reduced weight gain, whereas barley-containing diets that were supplemented with beta-glucanase increased weight gain. All oat bran and barley-containing diets lowered serum total cholesterol and low-density-lipoprotein (LDL) cholesterol relative to the corn control diet. LDL cholesterol was reduced more by oat bran supplemented with tocotrienols than by either oat bran or tocotrienols alone. There was no difference in LDL cholesterol levels between diets containing whole barley and barley from which beta-glucan, tocotrienols, or both had been removed. Inverse effects were noted on activities of 3-hydroxy-3-methylglutaryl Coenzyme A (HMG CoA) reductase, the rate-limiting enzyme of cholesterol synthesis, and cholesterol 7alpha-hydroxylase, involved in the degradation of cholesterol to bile acids. Oat bran plus tocotrienols, barley, and solvent-extracted barley decreased HMG CoA reductase by 50% and increased cholesterol 7alpha-hydroxylase by 100%; other diets had lesser, but significant effects. It was concluded that both beta-glucan and tocotrienols affected cholesterol levels and cholesterol metabolism, and the effects were additive or less. Removal of beta-glucan from barley diets abolished or diminished effects on enzyme activities but did not alter effects on cholesterol levels. This indicates the possibility of another component in barley that affected cholesterol levels by an unknown mechanism.