cholesterol.about.com
MECHANISM OF ACTION
The exact mechanism of oat beta-glucan's possible hypocholesterolemic effect is not clear. Oat beta-glucan does not appear to have any effect on the biosynthesis of cholesterol. It appears to promote increased excretion of bile acids, which could explain, in large part, its possible cholesterol-lowering activity. Oat beta-glucan may also promote cholesterol clearance from the plasma via reverse cholesterol transport.
The mechanism of the possible glucose-regulatory activity of oat beta-glucan is also not well understood. Oat beta-glucan may delay gastric emptying time and consequently affect the rate of uptake of D-glucose from the small intestine. This may be one possible mechanism; the high viscosity of oat beta-glucan may delay absorption of glucose, which may be another possible mechanism. Oat beta-glucan has been found to have immunomodulatory activity in tissue culture and in mice. It appears to activate macrophages to release certain cytokines. Such activity, in mice, has been found to be protective against bacterial infection. It is unclear whether oat beta-glucan has immunomodulatory activity in humans.
PHARMACOKINETICS
Following ingestion, there is virtually no digestion of oat beta-glucan in the small intestine. Some digestion of oat beta-glucan does take place in the large intestine via bacterial beta-glucosidases. Some smaller oligosaccharides produced by the bacterial transformation of oat beta-glucan may get absorbed, but this is unclear. A large percentage of the ingested beta-glucan is excreted in the feces.
INDICATIONS AND USAGE
Oat beta-glucan has hypocholesterolemic effects and may also favorably affect some other lipids. It has demonstrated some immune-enhancing effects and may be helpful in some with diabetes.
RESEARCH SUMMARY
Evidence that oat beta-glucan can reduce cholesterol levels was sufficient to induce the FDA to allow health claims on whole oat products that provide at least 0.75 grams of soluble fiber per serving. The allowed health claim is that these products reduce the risk of heart disease by reducing levels of cholesterol.
In one study, mildly hypercholesterolemic subjects on a "typical" diet, in which 35% of calories was derived from fat, were given an oat beta-glucan extract containing 1% or 10% oat beta-glucan. There was a significant reduction in total cholesterol levels in those receiving the 10% oat beta-glucan preparation after three weeks. Cholesterol levels declined significantly in the 1% group, as well, but not as quickly. There was also a significant decline in LDL-cholesterol levels in both groups. Triglyceride and HDL-cholesterol levels were not significantly changed. Some other studies have reported similar results.
Improved glucose and insulin responses have been reported in a study of moderately hypercholesterolemic healthy subjects. Oat extracts containing 1% and 10% beta-glucan both demonstrated these beneficial effects on glucose tolerance factors.
NIDDM patients given varying concentrations of oat beta-glucan also had significantly improved glucose and insulin responses. Higher doses of the oat beta-glucan correlated with greater improvement.
There are in vitro and animal studies demonstrating that oat beta-glucan, like those extracted from yeast and other fungi, has favorable immunomodulatory activities. These include the ability to activate macrophages and stimulate their release of interleukin (IL)-1 and tumor necrosis factor (TNF)-alpha, among other activities
Intraperitoneal administration of oat beta-glucan has enhanced a non-specific resistance to bacterial challenge in mice. Survival times have been improved in mice pre-treated with oat beta-glucan and then challenged with Staphylococcus aureus. Similarly, resistance to Eimeria vermiformis has been significantly increased in immunosuppressed mice given oat beta-glucan intragastrically or parenterally. |
