The oat grain is valued for its fiber content. The outer layer of the oat seed is referred to as oat bran. Oat bran is 30% dietary fiber by weight.
Oat bran causes few side effects when ingested, and can be cooked hot as a cereal or incorporated into foods, such as muffins. Oat bran is superior to cellulose, wheat, guar gum and beans as a fiber supplement. For example, guar gum can turn into a gummy-like material requiring quick digestion. Therefore, in cooking, its use is limited to a few bread formulations, crispbread or guar-pasta products. Wheat fiber and cellulose do not have the blood lipid and cholesterol-lowering benefits of oat bran. Beans can cause flatulence (gas). On a gram-equivalent basis, oat bran provides about four times as much water-soluble fiber as wheat bran.
Interest in oat bran came after a University of Kentucky College of Medicine researcher, Dr. James Anderson volunteered to be a "guinea pig" in cholesterol research. Over a period of ten weeks, he ate 3 ounces of oat bran a day, causing his cholesterol levels to drop a full 110 points. This finding is significant because decreases in serum cholesterol have been associated with a decreased risk of heart attack. When serum cholesterol level is lowered by 5 points, risk of having a heart attack is decreased by 10%. A 20 point reduction of serum cholesterol decreases the risk of heart attack by 40%.
Since Dr. Anderson's study, many well-controlled scientific studies have demonstrated oat bran has a hypocholesterolemic (cholesterol-lowering) effect, even in individuals who do not modify their intake of dietary cholesterol or fat. Further research has also shown oat bran can lower serum levels of low density lipoproteins (LDL), moieties which are thought to contribute to blockage of the arteries.
Oat bran aids in the control of obesity and in weight reduction. The soluble fiber in oat bran slows the rate at which the stomach empties and, thus, reduces the rate at which food is broken down and absorbed. The resulting extended period of satiety translates into a longer feeling of fullness and fewer pangs of hunger. Additionally, soluble fiber tends to reduce the fluctuations in blood glucose levels some people experience after a meal. It does this by slowing the rate at which the glucose is absorbed from the intestine and duodenum.
Method of Action
Oat bran has been found to have a bile-sequestering effect lowering cholesterol levels. Bile acids are necessary for the formation of micelles, responsible for the absorption of fat and cholesterol. When bile acids are bound to dietary fiber in the intestines, the absorption of fat and cholesterol from the gastrointestinal tract is impaired, resulting in decreased levels of total serum cholesterol. The following mechanisms have been proposed for oat bran's ability to reduce serum cholesterol.
First, as mentioned above, soluble fiber binds bile acids and other lipids and may interfere with micelle formation in the proximal small intestine. This interference would alter the quantity of cholesterol or fatty acids absorbed or the size of lipoprotein particles formed by the intestinal mucosa.
The second possibility suggests oat bran significantly increases the excretion of bile acids in the feces, and may therefore interfere with cholesterol and bile acid homeostatis sufficiently to affect production of lipoproteins in the liver. Another possibility suggests the soluble fiber of oat bran is fermented by bacteria in the colon to form gases and short chain fatty acids (acetate, butyrate, and propionate). These short chain fatty acids are almost completely absorbed into the portal vein and might affect the synthesis of cholesterol by the liver. Finally, oat bran may act like a bile-acid binding agent, and thus accelerate the removal of LDL from peripheral circulation.
Supplementing the diet with 100 grams of oat bran a day has been shown to lower LDL cholesterol concentrations without altering serum concentrations of HDL (good lipoprotein) cholesterol in hypercholesterolemic men. Serum cholesterol decreased an average of 19% at 21 days, while LDL cholesterol decreased nearly 22% in the same time period. Oat bran, 50 grams a day, produced similar reductions.
Similar effects were seen in young, healthy adults enrolled in a prospective, randomized, double-blind, controlled study. Those who ingested two oat bran muffins (with whole wheat flour, wheat bran, and oat bran present in a ratio of 1:2:3) a day over a 28 day period showed a 8.3% reduction in serum triglyceride values, a 5.3% reduction in serum total cholesterol, and an 8.7% reduction in LDL cholesterol. Subjects eating the same muffins but without oat bran saw no such changes. Similar results have also been reported in another healthy adult population when oat bran was incorporated into a fat-modified diet.
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