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a bit technical.... it's about how fibers (among which oa't's) help lowering LDL
Dietary fibres, which are resistant to digestion by enzymes in the gastrointestinal tract, can be divided into water-soluble and insoluble fibres. The water-soluble (or viscous) fibres, in particular, have long been recognised for their ability to lower serum cholesterol concentrations. The effective fibre from oats is beta-glucan.11 In 1997, the US FDA approved the health claim that "a diet high in soluble fibre from whole oats and low in saturated fat and cholesterol may reduce the risk of heart disease."12
To achieve a clinically relevant reduction in total serum cholesterol concentrations, a person would have to eat at least 3g beta-glucan per day from oats. Based on a meta-analysis, researchers estimated that such an amount of soluble fibres from oats lowered serum cholesterol concentrations an average of 0.13 mmol/L (5mg/dL) in subjects with a serum cholesterol concentration below 5.9 mmol/L (227mg/dL) and by 0.41 mmol/L (16mg/dL) in hypercholesterolemic subjects.13 In general, researchers did not observe an effect on HDL cholesterol or triacylglycerol concentrations. LDL cholesterol reductions were found to be dose dependent.13,14
Researchers have proposed several mechanisms to explain the cholesterol-lowering effect of beta-glucan. One hypothesis proposes that beta-glucan increases bile acid synthesis because the enterohepatic circulation of bile acids is reduced by intestinal binding of bile acids to beta-glucan.15,16 Alternatively, it is possible that the viscous beta-glucan acts as a physical barrier in the intestinal tract, blocking absorption of bile acids and cholesterol. Other researchers have postulated that soluble fibres are bacterially fermented in the colon, leading to the production of short-chain fatty acids, such as propionate, which may lower hepatic cholesterol synthesis.17
Researchers also have suggested that, particularly in the postprandial state, soluble fibres lower insulin levels, which is also known to lower cholesterol synthesis.18 However, researchers have not found changes in serum cholesterol-precursor concentrations after oat consumption, suggesting that these latter two explanations are not likely correct.19
Numerous well-controlled trials did not demonstrate a beneficial effect of beta-glucan from oats on the serum lipoprotein profile.20-23 Possible explanations for these inconsistent results may be differences in the viscosity of the beta-glucan or detrimental effects of food manufacturing on its viscous characteristics. Elucidating the exact mechanism underlying the cholesterol-lowering effects of beta-glucan may be helpful to explain these apparent discrepancies.
In addition to the soluble fibres from oats, viscous fibres from other sources also may have favourable effects on serum lipoprotein profiles. Beta-glucan from barley and yeast sources, for example, also appear to be effective.24,25
Also in this respect, the US FDA has approved a cholesterol-reducing health claim for psyllium, a soluble fibre isolated from the psyllium seed husk (PSH).26 To achieve a significant reduction in total cholesterol levels, subjects must take at least 10.2g PSH supplying 7g soluble fibre daily (four servings each containing 1.7g soluble fibre) as part of a diet with low saturated fat and cholesterol levels. From three different meta-analyses, taking 910g PSH a day lowers serum LDL cholesterol concentrations by 6.0-7.4 per cent. In contrast to beta-glucan, PSH-induced cholesterol reductions do not seem to be associated with initial cholesterol concentrations.27-29
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11. Braaten JT, et al. Oat b-glucan reduces blood cholesterol concentrations in hypercholesterolemic subjects. Eur J Clin Nutr 1994;48:465-74.
12. FDA Talk Paper; http://www.cfsan.fda.gov/~lrd/tpoats.html.
13. Ripsin CM, et al. Oat products and lipid lowering. A meta-analysis. JAMA 1992;267:3317-25.
14. Davidson MH, et al. The hypocholesterolemic effects of beta-glucan in oatmeal and oat bran. JAMA 1991;265:1833-9.
15. Kritchevski D, Story JA. Binding of bile salts in vitro by non-nutritive fibre. J Nutr 1974;104:458-64.
16. Bell S, et al. Effect of beta-glucan from oats and yeast on serum lipids. Crit Rev Food Sci Nutr 1999;39:189-202.
17. Thacker PA, et al. Influence of propionic acid on cholesterol metabolism of pigs fed hypercholesterolemic diets. Can J Anim Sci 1981;61:969-75.
18. Bourbon I, et al. Postprandial lipid, glucose, insulin, and cholecystekonin responses in men fed barley pasta enriched with beta-glucan. Am J Clin Nutr 1999;69:55-63.
19. Uusitupa MI, et al. Lathosterol and other non-cholesterol sterols during treatment of hypercholesterolemia with beta-glucan-rich oat bran. Eur J Clin Nutr 1997;51:607-11.
20. Lovegrove JA, et al. Modest doses of b-glucan do not reduce concentrations of potentially atherogenic lipoproteins. Am J Clin Nutr 2000;72:49-55.
21. Torronen R, et al. Effects of an oat bran concentrate on serum lipids in free-living men with mild to moderate hypercholesterolemia. Eur J Clin Nutr 1992;46:621-7.
22. Beer MU, et al. Effects of oat gum on blood cholesterol levels in healthy young men. Eur J Clin Nutr 1996;49:274-5.
23. Leadbetter J, et al. Effects of increasing quantities of oat bran in hypercholesterolemic people. Am J Clin Nutr 1991;54:841-5.
24. McIntosh GH, et al. Barley and wheat foods: influence on plasma cholesterol concentrations in hypercholesterolemic men. Am J Clin Nutr 1991;53:1205-59.
25. Nicolosi R, et al. Plasma lipid changes after supplementation with b-glucan fibre from yeast. Am J Clin Nutr 1999;70:208-12.
26. FDA Talk Paper: http://www.cfsan.fda.gov/~lrd/tpsylliu.html.
27. Olson BH, et al. Psyllium-enriched cereals lower blood total cholesterol and LDL cholesterol, but not HDL cholesterol, in hypercholesterolemic adults: results of a meta-analysis. J Nutr 1997;127:1973-80.
28. Brown L, et al, Cholesterol-lowering effects of dietary fibre: a meta-analysis. Am J Clin Nutr 1999;69(1):30-42.
29. Anderson JW, et al. Cholesterol-lowering effects of psyllium intake adjunctive to diet therapy in men and women with hypercholesterolemia: analysis of 8 controlled trials. Am J Clin Nutr 2000;71:472-9.
Dietary fibres, which are resistant to digestion by enzymes in the gastrointestinal tract, can be divided into water-soluble and insoluble fibres. The water-soluble (or viscous) fibres, in particular, have long been recognised for their ability to lower serum cholesterol concentrations. The effective fibre from oats is beta-glucan.11 In 1997, the US FDA approved the health claim that "a diet high in soluble fibre from whole oats and low in saturated fat and cholesterol may reduce the risk of heart disease."12
To achieve a clinically relevant reduction in total serum cholesterol concentrations, a person would have to eat at least 3g beta-glucan per day from oats. Based on a meta-analysis, researchers estimated that such an amount of soluble fibres from oats lowered serum cholesterol concentrations an average of 0.13 mmol/L (5mg/dL) in subjects with a serum cholesterol concentration below 5.9 mmol/L (227mg/dL) and by 0.41 mmol/L (16mg/dL) in hypercholesterolemic subjects.13 In general, researchers did not observe an effect on HDL cholesterol or triacylglycerol concentrations. LDL cholesterol reductions were found to be dose dependent.13,14
Researchers have proposed several mechanisms to explain the cholesterol-lowering effect of beta-glucan. One hypothesis proposes that beta-glucan increases bile acid synthesis because the enterohepatic circulation of bile acids is reduced by intestinal binding of bile acids to beta-glucan.15,16 Alternatively, it is possible that the viscous beta-glucan acts as a physical barrier in the intestinal tract, blocking absorption of bile acids and cholesterol. Other researchers have postulated that soluble fibres are bacterially fermented in the colon, leading to the production of short-chain fatty acids, such as propionate, which may lower hepatic cholesterol synthesis.17
Researchers also have suggested that, particularly in the postprandial state, soluble fibres lower insulin levels, which is also known to lower cholesterol synthesis.18 However, researchers have not found changes in serum cholesterol-precursor concentrations after oat consumption, suggesting that these latter two explanations are not likely correct.19
Numerous well-controlled trials did not demonstrate a beneficial effect of beta-glucan from oats on the serum lipoprotein profile.20-23 Possible explanations for these inconsistent results may be differences in the viscosity of the beta-glucan or detrimental effects of food manufacturing on its viscous characteristics. Elucidating the exact mechanism underlying the cholesterol-lowering effects of beta-glucan may be helpful to explain these apparent discrepancies.
In addition to the soluble fibres from oats, viscous fibres from other sources also may have favourable effects on serum lipoprotein profiles. Beta-glucan from barley and yeast sources, for example, also appear to be effective.24,25
Also in this respect, the US FDA has approved a cholesterol-reducing health claim for psyllium, a soluble fibre isolated from the psyllium seed husk (PSH).26 To achieve a significant reduction in total cholesterol levels, subjects must take at least 10.2g PSH supplying 7g soluble fibre daily (four servings each containing 1.7g soluble fibre) as part of a diet with low saturated fat and cholesterol levels. From three different meta-analyses, taking 910g PSH a day lowers serum LDL cholesterol concentrations by 6.0-7.4 per cent. In contrast to beta-glucan, PSH-induced cholesterol reductions do not seem to be associated with initial cholesterol concentrations.27-29
===========================================
11. Braaten JT, et al. Oat b-glucan reduces blood cholesterol concentrations in hypercholesterolemic subjects. Eur J Clin Nutr 1994;48:465-74.
12. FDA Talk Paper; http://www.cfsan.fda.gov/~lrd/tpoats.html.
13. Ripsin CM, et al. Oat products and lipid lowering. A meta-analysis. JAMA 1992;267:3317-25.
14. Davidson MH, et al. The hypocholesterolemic effects of beta-glucan in oatmeal and oat bran. JAMA 1991;265:1833-9.
15. Kritchevski D, Story JA. Binding of bile salts in vitro by non-nutritive fibre. J Nutr 1974;104:458-64.
16. Bell S, et al. Effect of beta-glucan from oats and yeast on serum lipids. Crit Rev Food Sci Nutr 1999;39:189-202.
17. Thacker PA, et al. Influence of propionic acid on cholesterol metabolism of pigs fed hypercholesterolemic diets. Can J Anim Sci 1981;61:969-75.
18. Bourbon I, et al. Postprandial lipid, glucose, insulin, and cholecystekonin responses in men fed barley pasta enriched with beta-glucan. Am J Clin Nutr 1999;69:55-63.
19. Uusitupa MI, et al. Lathosterol and other non-cholesterol sterols during treatment of hypercholesterolemia with beta-glucan-rich oat bran. Eur J Clin Nutr 1997;51:607-11.
20. Lovegrove JA, et al. Modest doses of b-glucan do not reduce concentrations of potentially atherogenic lipoproteins. Am J Clin Nutr 2000;72:49-55.
21. Torronen R, et al. Effects of an oat bran concentrate on serum lipids in free-living men with mild to moderate hypercholesterolemia. Eur J Clin Nutr 1992;46:621-7.
22. Beer MU, et al. Effects of oat gum on blood cholesterol levels in healthy young men. Eur J Clin Nutr 1996;49:274-5.
23. Leadbetter J, et al. Effects of increasing quantities of oat bran in hypercholesterolemic people. Am J Clin Nutr 1991;54:841-5.
24. McIntosh GH, et al. Barley and wheat foods: influence on plasma cholesterol concentrations in hypercholesterolemic men. Am J Clin Nutr 1991;53:1205-59.
25. Nicolosi R, et al. Plasma lipid changes after supplementation with b-glucan fibre from yeast. Am J Clin Nutr 1999;70:208-12.
26. FDA Talk Paper: http://www.cfsan.fda.gov/~lrd/tpsylliu.html.
27. Olson BH, et al. Psyllium-enriched cereals lower blood total cholesterol and LDL cholesterol, but not HDL cholesterol, in hypercholesterolemic adults: results of a meta-analysis. J Nutr 1997;127:1973-80.
28. Brown L, et al, Cholesterol-lowering effects of dietary fibre: a meta-analysis. Am J Clin Nutr 1999;69(1):30-42.
29. Anderson JW, et al. Cholesterol-lowering effects of psyllium intake adjunctive to diet therapy in men and women with hypercholesterolemia: analysis of 8 controlled trials. Am J Clin Nutr 2000;71:472-9.
