We know from commercials that oats can lower blood cholesterol, but the ads never tell us how it works- or what types of oats work the best. It turns out that oats work to lower cholesterol- particularly the low density lipoprotein (LDL), the bad one- in several ways. The cholesterol cycle in the body is somewhat complicated, with both the liver and the intestines involved. Oats interrupt this cycle at several points.
On the most basic level, oats contain a lot of fiber and so make you fill full faster, thus preventing you from eating more than you need. Excess weight can lead to excess cholesterol.
The liver makes cholesterol from bile acid, which it secretes into the intestine. Oat bran contains beta-glucan, which, among other things, absorbs bile acid from the bowels. Without this bile acid being returned to the liver, the liver has to create more- and it makes it by pulling low density cholesterol from the blood stream. (Note: drugs like Questan work in this same way, but cost a lot more than oatmeal does and can have side effects)
Oat bran also thickens the water in the intestines. This means that less cholesterol gets through the water to be absorbed from your food. It also slows the absorption of glucose, which means the body is not provoked into making excess insulin. Excess insulin causes the liver to make more LDL cholesterol.
When beta-glucan ferments in the intestines, it creates short-chain fatty acids, which are absorbed by the colon and from there go to the liver. Once in the liver, they interfere with the main enzyme that produces cholesterol. This is the same mechanism that statin drugs use to reduce LDL cholesterol.
Oats also have a unique antioxidant, avenanthramides, that protects the LDL cholesterol from oxidation. This same antioxidant decreases the inflammatory response of the arterial walls, which means less plaque sticks to the inside of the arteries, which means less clogging.
On top of this, oats have a high amount of the amino acid arginine. Arginine works against clogging of the arteries in multiple ways. It decreases the production of LDL cholesterol and facilitates its breakdown. It’s a precursor to nitric oxide, which relaxes the arterial walls and thus lowers blood pressure. It decreases platelet stickiness, thus reducing clot formation. As a bonus, it’s an immune system booster.
The type of oats you eat makes a difference in how effective they are. Old fashioned oats are the best, quick cook oats are next, with instant oatmeal coming in a low third. The more processed the oats are, the less beta-glucan remains. Oat bran is the most concentrated source of beta-glucan, but it’s not easy to use. It’s gummy and sticky, but it can be added to breads, pancakes and muffins. Cheerios, as the ads say, have heart healthy beta-glucan, but it’s not a very concentrated source. It’s good for a quick breakfast, though, or a snack.
Oats sound like a miracle food, something too good to be true, but many rigorous studies have proved the claims are true. Because they work to lower LDL cholesterol and reduce artery clogging in so many different ways, they should be a first line of defense. Statin drugs lower cholesterol but they only work on one level; even if you have to take a statin drug, oats will help you keep the dose of statins low and work on other parts of the cholesterol system.
Cholesterol Down, by Janet Bond Brill, Ph.D., R.D., LDN
Nutrition Journal: http://www.nutritionj.com/content/6/1/6 (for description of how beta-glucan works)
USDA: http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=226131 (mechanism of avenanthramides)