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Role of Phytosterols In Reducing Cholesterol

Phytosterols, or plant sterols, are important structural components of plant membranes that occur naturally and resemble cholesterol, but have different configurations. Phytosterols are important compounds in pharmaceuticals (production of therapeutic steroids), nutrition (anti-cholesterol additives in foods, anti-cancer properties), and cosmetics (creams, lipstick). Phytosterols can be obtained from vegetable oils or from industrial wastes (grain bran).

Phytostanols are a fully-saturated subgroup of phytosterols (contain no double bonds). Phytostanols occur in trace levels in many plant species and they occur in high levels in tissues of only a few cereal species. Phytosterols can be converted to phytostanols by chemical hydrogenation.

More than 200 different types of phytosterols have been reported in plant species. In addition to the free form, phytosterols occur as four types of "conjugates," in which the 3-OH group is esterified to a fatty acid or a hydroxycinnamic acid, or glycosylated with a hexose (usually glucose) or a 6-fatty-acyl hexose.


Role in Lowering Cholesterol Levels

While all modern diet recommendations for LDL levels ("bad" cholesterol) focus on reducing the consumption of dietary saturated fat and increasing the consumption of dietary fiber, other dietary components such as phytosterols may have equivalent or even larger effects on blood cholesterol.

It has been well established that plant sterols inhibit cholesterol absorption in the intestine and lower plasma cholesterol concentration in animals and humans. Studies showed that plant sterols prevented micellar solubility of cholesterol by being dissolved in bile salt micelles instead of cholesterol and hence, limited cholesterol absorption. The ability to reduce micellar solubility of cholesterol is highest in sitostanol, intermediate in sitosterol and stigmasterol and lowest in brassicasterol and campesterol. Phytosterols reduce cholesterol absorption while being poorly-absorbed themselves.

Not All Oils Are Created Equal All commercial vegetable oils contain phytosterols and the levels of phytosterols in all are less than 1%. To consume enough phytosterols to significantly reduce serum cholesterol levels (1-3 grams), one would need to consume at least 100 grams (~900 calories) of oil per day, an amount that is impractical and unhealthy. Furtunately, oils extracted from some grains and grain-processing fractions contain much higher levels of phytosterols than commercial vegetable oils. Corn fiber oil and barley kernel oil contain 10-15% and 3-5% of total phytosterols, respectively.

Unfortunately, phytosterols of most vegetable oils are often lost during the normal refining process which utilizes a caustic sodium hydroxide step. Thus, oils high in phytosterols such as extra virgin olive oil, rice bran oil, corn fiber oil, oat oil, wheat germ oil and soy germ oil, to name a few are depleted of these compounds during the refining process. There have been published reports, in the case of olive oil which have demonstrated that depending upon the refining process, its cholesterol-lowering and anti-oxidant properties are significantly altered as you move from extra-virgin to refined olive oil.3

There is an environmentally-safe technology used in extracting phytosterols from corn fiber oil is called Supercritical Fluid Extraction (SFE) doesn't use chemical extraction solvents and provides high yield of phytosterols.


Corn Fiber Oil and Drug-free Control of Cholesterol Levels

Agricultural Research Service (ARS) scientists have developed a method for preparing corn fiber oil, which allows corn aleurone cells to be recovered from the process. Corn aleurone cells provide higher oil yields than corn fiber. Corn fiber is comprised of about one-third aleurone cells and two-thirds other fibrous material. This means corn aleurone cells contain three times more oil than corn fiber—so about three times more phytosterol-rich oil can be obtained by extracting the same amount of material.2

Corn fiber is a byproduct of the wet milling process–-a process to remove the starch from corn. Corn fiber is the richest known source of natural phytosterols. Phytosterols block the absorption of dietary cholesterol in the body. Corn fiber oil contains about 10 times more phytosterols than regular corn oil. It can potentially lower serum cholesterol by 10-15%.

Barley Oil

Barley kernels have been reported to contain several types of nutraceutical compounds that have health-promoting properties. These include phytosterols, and tocopherols and tocotrienols, which are vitamin E analogues that are potent antioxidants and are thought to be important for cardiovascular health. Most barley that is used in food products is "pearled" or "scarified" to abrade and remove the fibrous hull, which improves the flavor and also creates pearled kernels that are enriched in starch, protein, and other nutrients. Studies show that the levels of total phytosterols and total tocotrienols in the oils prepared from both whole kernels and scarified fines contain 2911 to 6126 mg/kg oil, which are several-fold higher than those reported to occur in two other oils that are being marketed as "high in tocotrienols" - palm oil (530 mg/kg) and rice bran oil (770 mg/kg). The levels of total phytosterols in barley oils are also sufficiently high (0.18 to 1.44 g/15 g oil) to significantly lower LDL-cholesterol at reasonable dosages of 15 ml/day (1 tsp/day).1

In the last several years several spreads including Benecol, Take Control and Smart Balance were shown to significantly lower serum cholesterol at dosages of 1-3 grams per day. The popularity of these products has caused the medical and biochemical community to focus much attention on phytosterols and consequently research activity on phytosterols has increased dramatically.

Phytosterols in Other Foods

Since phytosterol-enriched margarine spreads have reported significant decreases in total and low-density cholesterol (LDL) in people with both normal and high cholesterol levels, phytosterols are introduced in other, lower-fat products such as flavanol-rich cocoa snack food containing phytosterols. Studies showed that people who consumed two servings per day had a significant reductions in plasma total and LDL cholesterol, and the ratio of total to high-density lipoprotein cholesterol (HDL). Phytosterols did not affect the levels of high-density lipoprotein cholesterol (HDL, or "good" cholesterol), triglycerides, or lipid-adjusted lycopene, beta-cryptoxanthin, lutein/zeaxanthin, alpha-carotene levels, or levels of serum vitamins A or E.

Phytosterols and Congestive Heart Disease (CHD)

It turns out that the benefits of phytosterols are not limited to their cholesterol lowering abilities. Researchers have found that phytosterols reduces the concentrations of high-sensitivity C-reactive protein (hs-CRP), the marker of inflammation which is believed to trigger the development of atherosclerosis. In one study, seventy-two healthy individuals received a reduced-calorie phytosterol-enriched orange juice beverage in concentration of 1 g per 8 ounces twice a day with meals for 8 wk. Phytosterol-enriched beverage supplementation significantly reduced total cholesterol (5%;) and LDL cholesterol (9.4%), increased HDL cholesterol and resulted in a significant reduction of high-sensitivity C-reactive protein concentrations.


References

  1. The Composition of Functional Lipids in Hulled and Hulless Barley, in Fractions Obtained by Scarification and in Barley Oil
  2. New Method for Preparing Corn Fiber Oil
  3. High Phytosterol Oils from Corn Fiber and Barley


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