Despite the decline in the incidence of and death from coronary heart disease (CHD) in recent decades, CHD is still one of the leading causes of mortality and morbidity. The link between elevated plasma LDL-cholesterol concentrations and the risk of developing coronary artery disease has been clearly established [1] . The National Cholesterol Education Program (NCEP) recommends a list of complicated and grindingly diet for the hypercholesterolemic people but got ineffective results. Not included in NCEP guidelines are specific recommendations about dietary fiber, which attracted wider concern.
Since 1953 Hipsley first introduced this new terminology "dietary fiber (DF)", it has become today's most active content in nutritional study. For more than 50 years, the researchers have accumulated a lot of beneficial information of dietary fiber and as an important component of dietary fiber and oat glucan has also aroused great concern. In the early 1960s, De Groot et al. discovered that the daily consumption of bread containing 140 g rolled oats markedly lowered serum cholesterol concentrations in humans [2]. In March of 1995, the Quaker Oats Co., Barrington, Ill., petitioned the United States Food and Drug Administration (FDA) for permission to make a health claim that oat products may reduce the risk of heart disease; the petition was granted in January 1997. This was the first time that such a claim was allowed for a specific food. The FDA reviewed over 37 studies demonstrating that oat-bran (and in particular beta-glucan) lowered serum cholesterol. The claim is as follows: "Soluble fiber from oatmeal, as part of a low saturated fat, low cholesterol diet, may reduce the risk of heart disease [3] "
Since the FDA issued this health claim, people have designed a variety of tests to prove that oat beta-glucan indeed plays an important role in reducing serum cholesterol levels.
Researchers from the Center for Cardiovascular Disease Control (CCDC) in United States found that adequate supplementary of beta-glucan fiber can reduce the blood lipids [4]. The researchers selected 15 free-living, obese, hypercholesterolemic men. After a 3-wk period in which subjects ate their usual diet, 15 g fiber/d was added to the diet for 8 wk and then stopped for 4 wk. Plasma lipids were measured weekly during baseline and at week 7 and 8 of fiber consumption, and again at week 12. Both total cholesterol and HDL-cholesterol concentrations were measured directly. The concentrations of LDL-cholesterol were calculated. They found that after supplementation, serum total cholesterol concentration was significantly lower (7 %) than at baseline; meanwhile, HDL-cholesterol concentrations increased significantly (12 %) and was well tolerated. This suggested that beta-glucan can effectively restrain the concentration of LDL-cholesterol in plasma.
Dutch researchers published a study in the latest "American Journal of Clinical Nutrition" indicated that adding beta-glucan into fruit juice can help lower the level of total cholesterol and the harmful LDL-cholesterol in the human body. Ronald P group of University of Maastricht, the Netherlands, selected 25 healthy people to drink fruit juice containing oat beta-glucan. As a control, another 22 healthy people drink ordinary juice. All subjects drink specific fruit juice in consecutive 5 wk. In this study, this group collected blood samples both before and after test respectively, then measure the consentration of fat, lipoprotein and fat-soluble antioxidant. They reported that compared to the control group, the concentration of total cholesterol reduced by 4.8 % and LDL-cholesterol reduced by 7.7 % in the group of who intaked beta-glucan. He said that they were still unclear the principle how beta-glucan lower the LDL-cholesterol. He guessed that beta-glucans may affect the intestinal secretion of bile acid and accelerate the synthesis and secretion of bile acid, which need more cholesterol.
A recent meta-analysis of previously published data revealed a connection between soluble fiber intake from oat products and a reduction in total and LDL cholesterol [5].
Mechanisms of action of beta-glucans: lipid-lowering effect
Since the discovery of the cholesterol-lowering action of rolled oats, much effort has been put into identification of the underlying mechanisms. Four mechanisms have been proposed to explain how beta-glucan from oats lowers serum cholesterol.
First, it has been postulated that soluble fiber binds to bile acids in the intestinal lumen, which results in a reduced bile acid pool circulating back to the liver. This binding action stimulates production of more bile acids derived from cholesterol that is either made endogenously or captured from the circulation [6-9].
Second, soluble fibers are fermented in the large bowel by colonic bacteria [6, 9-11]. This action results in the production of the short-chain fatty acids (SCFAs) - acetate, propionate, and butyrate. These SCFAs are absorbed through the portal vein, inhibiting hepatic cholesterol synthesis by limiting the action of HMG-CoA reductase (the rate-limiting enzyme required for cholesterol biosynthesis) or by increasing catabolism of LDL-C.
Third, soluble fiber may delay gastric emptying, thereby reducing post-prandial serum insulin concentrations [12]. This action reduces hepatic cholesterol production through mediation of HMG-CoA reductase.
Fourth, oat soluble fiber may interfere with the absorption of dietary fat, including cholesterol, by increasing intestinal viscosity [12]. The increased viscosity causes the digesta to hold on to extra water, which slows its movement.
However, these guidelines only consider the total content of beta-glucans in a certain food but not their molecular weight [13]. Animal studies suggested that molecular weight is an important determinant of the lipid-lowering properties of oat fiber [14-16]. Researchers in Swedish University of Agricultural Sciences selected 22 healthy people. The two different oat breads with similar nutrient composition but different beta-glucan molecular weight (797 kDa & 217 kDa) distribution were fed to 22 volunteers in a randomized, double-blind, crossover design for 3 wk. Blood samples were drawn and analyzed for lipids, insulin, and glucose. Compared to baseline, females who consumption of HMW bread reudced serum LDL-cholesterol but no significant changes in males. Neither males nor females who consumed LMW bread showed no significant changes of LDL-cholesterol. These results suggest that the molecular weight, bread production decreased the molecular weight of beta-glucan and that consumption of these breads caused no appreciable cholesterol-lowering effect [17].
Therefore, it is the requiring urgent issues in current researches that how to find the optimum molecular weight beta-glucan thus to better exert its lipid-lowering activity. In addition, researchers also pay close attention to the field whether there are other more effective mechanisms. Putus Macromolecular Sci. & Tech. Ltd. is an international corporation which has been putting effort in research, development and application of a variety of carbohydrate (polysaccharides) polymers. We are manufacturing and providing high quality carbohydrate polymer standards with unique structure and high chemical uniformity in terms of molecular weight (Mw) and degree of branching. Putus is now providing PS-OBGs, the aqueous polymer standards originated from oat bran. Our research showed that PS-OBG standard possesses a linear chain with mixed linkage of (1-3) and (1-4). There are two products suit the lipid-lowering study: PS-OBG-Vis, with three different specifications (high, medium, low) of viscosity and molecular weight, which show the purity as high as 97%; In addition, Putus provides PS-OBG-Mw, a new carbohydrate polymer molecular weight (Mw) standards with Mw distribution (MwD) of 1.01-1.05 (For more detailed molecular weight and polydispersity please consult Products Information). These non-starch, non-protein and other impurities, water-soluble, highly stable standards will undoubtedly make up the defects of current beta-glucan samples in both domestic and international research, and will provide a strong guarantee on obtaining more accurate results and more stable experimental data.
References
[1] Expert Panel on Detection, Evaluation, and Treatment of High Cholesterol in Adults. Summary of the second report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel II). Journal of American Medical Association, 1993, 269: 3015-23.
[2] A.P. De Groot, R. Luyken, N.A. Pikaar. Cholesterol lowering effect of rolled oats. Lancet, 1963, 2: 291-300.
[3] S. Bell, V.M. Goldman, B.R. Bistrian, A.H. Arnold, G. Ostroff, R.A. Forse. Effect of beta-glucan from oats and yeast on serum lipids. Clinical Reviews in Food Science and Nutrition. 1999, 39(2): 189-202.
[4] R. Nicolosi, S.J. Bell, B.R. Bistrian, I. Greenberg, R.A. Forse, G.L. Blackburn. Plasma lipid changes after supplementation with b-glucan fiber from yeast. The American Journal of Clinical Nutrition. 1999, 70: 208-212.
[5] L. Brown, B. Rosner, W.W. Willett, F.M. Sacks. Cholesterollowering effects of dietary fiber: a meta-analysis. The American Journal of Clinical Nutrition. 1999, 69: 30-42.
[6] S.R. Glore, D. Van Treeck, A.W. Knehans, M. Guild. Soluble fiber and serum lipids: a literature review. Journal of American Dietet Association. 1994, 94: 425.
[7] A. Lia, H. Andersson, N. Mekki, C. Juhel, M. Senft, D. Lairon Postprandial lipemia in relation to sterol and fat excretion in ileostomy subjects given oat-bran and wheat with meals. The American Journal of Clinical Nutrition. 1997, 66: 357-65.
[8] J.H. Cummings, G.T. Macfarlane. Colonic microflora: nutrition and health. Nutrition, 1997, 13: 476-478.
[9] R.W. Kirby, J.W. Anderson, B. Sieling, E.D. Rees, W.J.L. Chen, R.E. Miller, R.M. Kay. Oat-bran intake selectively lowers serum low-density lipoprotein cholesterol concentrations of hypercholesterolemic men. The American Journal of Clinical Nutrition. 1981; 34: 824-829.
[10] J.W. Anderson, L.S. Story, B. Sieling, W.J.L. Chen, M.S. Petro, J. Story. Hypocholestero -lemic effects of oat-bran or beans intake for hypercholesterolemic men, The American Journal of Clinical Nutrition. 1984, 40: 1146-1155.
[11] J.M. Keenan, J.B. Wenz, S. Myers, C.M. Ripsin, Z. Huang. Randomized, controlled, cross-over trial of oat bran in hypercholesterolemic subjects. Journal of Family Practice. 1991, 33: 600-8.
[12] S. Inks, R. Mathews. Oatmeal and oat-bran: heart healthy benefits and more. New Technologies for Healthy Foods and Nutraceuticals. 1997.
[13] U.S. Food and Drug Administration FDA final rule for federal labeling: health claims; oats and coronary heart disease. Federal Regist. 1997, 62: 3584-3681.
[14] J.L. Tietyen, , D.J. Nevins, B.O. Schneeman, Characterization of the hypercholesterole -mic potential of oat bran. FASEB. 1990, 4: A527.
[15] S. Bengtsson, P. Åman, H. Graham, C.W. Newman, R.K. Newman. Chemical studies on mixed-linked beta-glucans in hull-less barley cultivars giving different hypocholesterolae -mic responses in chickens. Journal of Science Food and Agriculture. 1990, 52: 435-445.
[16] K.E. Bach Knudsen, I. Hansen, B.B. Jensen, K. Østergård. Physiological implications of wheat and oat dietary fiber. New Developments in Dietary Fiber. 1990, 135-150.
[17] J. Frank, B. Sundberg, A. Kamal-Eldin, B. Vessby, P. Åman. Yeast-leavened oat breads with high or low molecular weight beta-glucan do not differ in their effects on blood concentrations of lipids, insulin, or glucose in humans. Journal of Nutrition. 2004, 134: 1384-1388.
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