Beta-glucan is the soluble, viscous polysaccharide that is the primary active component of the oat and barley fibre — it is the fibre that is responsible for the cholesterol-lowering effect of the oats and for the FDA-approved health claim that “3g of beta-glucan daily from oats may reduce the risk of the coronary heart disease.” The beta-glucan is a linear polysaccharide consisting of the glucose units linked by the beta-1,3 and the beta-1,4 glycosidic bonds, and it is the beta-1,3 linkages that create the branching points that give the beta-glucan its soluble, viscous properties. This viscosity is the key to its physiological effect — the viscous beta-glucan forms a gel in the intestine that traps the bile acids and the cholesterol-rich micelles, preventing their reabsorption and increasing their excretion in the faeces. The liver then synthesises the new bile acids from the cholesterol in the blood (using the cholesterol to replace the bile acids that were excreted), and this reduction in the hepatic cholesterol then leads to the upregulation of the LDL receptors on the hepatocyte surface and the increased clearance of the LDL cholesterol from the blood — lowering the LDL cholesterol by 5-10% in people who consume 3-5g of beta-glucan daily. The typical dietary beta-glucan intake from the oats is 1.5-3g daily (from one to two servings of the oat bran or the oatmeal), and the optimal intake for the cholesterol reduction is 3-5g daily — which corresponds to approximately 75-100g of the dry oat bran or to 50-75g of the dry rolled oats daily. The beta-glucan deficiency is therefore common in people who do not eat the oats or the barley regularly, and it is one of the most important modifiable risk factors for the cardiovascular disease.
Beta-Glucan and the Cholesterol Metabolism
The beta-glucan lowers the LDL cholesterol by interrupting the enterohepatic circulation of the bile acids — the viscous beta-glucan traps the bile acids and the cholesterol-rich micelles in the intestine, preventing their reabsorption and increasing their excretion in the faeces. The liver responds to this loss of bile acids by upregulating the 7-alpha-hydroxylase enzyme (the rate-limiting enzyme of the bile acid synthesis) and by synthesising new bile acids from the hepatic cholesterol pool. This depletes the hepatic cholesterol, which then activates the SREBP-2 transcription factor (sterol regulatory element-binding protein-2), which upregulates the LDL receptor gene transcription and increases the LDL receptor density on the hepatocyte surface. The increased LDL receptor density then clears more LDL cholesterol from the blood, lowering the serum LDL cholesterol by 5-10% — which corresponds to a 10-20% reduction in the risk of the coronary heart disease per 0.6mmol/L (23mg/dL) reduction in the LDL cholesterol. This beta-glucan-induced LDL cholesterol reduction is one of the most consistent and most well-established effects of any dietary fibre, and it has been confirmed in over 50 RCTs and in multiple meta-analyses.
The clinical importance of the beta-glucan for the cardiovascular health is underscored by the observation that the regular consumption of the oat beta-glucan reduces the LDL cholesterol and reduces the risk of the coronary heart disease. A meta-analysis of 28 RCTs in over 3000 participants found that the beta-glucan supplementation at 3-5g daily significantly reduced the LDL cholesterol (by 0.2-0.3mmol/L, or approximately 8-12mg/dL), reduced the total cholesterol (by 0.3-0.4mmol/L), and reduced the coronary heart disease risk (by 10-15%) — making the beta-glucan one of the most effective dietary interventions for the prevention of the cardiovascular disease, alongside the plant sterols, the stanols, the soluble fibres, and the omega-3 fatty acids.
Practical Application
For general beta-glucan supplementation for the cholesterol reduction and for the cardiovascular health, the evidence-based approach is to consume 3-5g of beta-glucan daily from the oat bran, the oat flour, the rolled oats, or the beta-glucan supplement (which is available in the capsule and the powder form). The beta-glucan should be consumed with the main meals (to maximise the bile acid trapping and the cholesterol excretion), and it should be introduced gradually (to allow the gut microbiota to adapt to the increased fibre intake and to minimise the gastrointestinal symptoms). The FDA allows the health claim for the beta-glucan from the oats (but not from the barley, unless it is specifically qualified), and it requires at least 3g of beta-glucan daily from the oats for the health claim to be applicable. For comprehensive cholesterol and cardiovascular support, beta-glucan pairs well with the plant sterols and stanols (which inhibit the cholesterol absorption in the intestine and which work synergistically with the beta-glucan for the LDL cholesterol reduction), with the niacin (which raises the HDL cholesterol and lowers the triglycerides and which has complementary effects on the lipid profile), with the red yeast rice (which contains the natural statins that inhibit the HMG-CoA reductase and which works synergistically with the beta-glucan for the cholesterol reduction), and with the CoQ10 (which protects the heart muscle from the statin-induced damage and which is depleted by the statin therapy).
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