June 10, 2006
Q: What are phytoserols and what are they good for? - Layperson
Combination products include Phytosterol Complex w/Beta Sitosterol (Source Naturals).
Phytosterols (also see Phytostanols and Beta-Sitosterol), widely found in the plant kingdom, are chemically similar to cholesterol. Cholesterol, however, only occurs in animals and is not found in plants. The cylclopentanoper- hydrophenanthrene ring structure of the sterol molecule is common to all sterols; the differences are primarily in the structure of the side chains.
Phytosterols are present in the diet. Typical daily dietary intakes of phytosterols range from 100 to 300 milligrams. It is higher in vegetarians. There are over 40 phytosterols, but beta-sitosterol is the most abundant one, comprising about 50% of dietary phytosterols. The next most abundant phytosterols are campesterol (about 33%) and stigmasterol (about 2 to 5%). Other phytosterols found in the diet include brassicasterol, delta-7-stigmasterol and delta-7-avenasterol.
Beta-sitosterol differs from cholesterol by the presence of an ethyl group at
the 24th carbon position of the side chain. In the case of
campesterol, this position is occupied by a methyl group. Chemically, the
phytosterols are classified as 4-desmethylsterols of the cholestane series.
Beta-sitosterol has the following chemical structure:
Phytosterols are potentially atherogenic like cholesterol, but except in the rare genetic disorders, sitosterolemia and cerebrotendinotic xanthomatosis, they are not. This is because so little of the phytosterols are absorbed. On the other hand, phytosterols can lower cholesterol levels. As early as 1951, it was shown that phytosterols lowered cholesterol in chickens, and subsequently they were found to lower cholesterol in humans. Recently, functional foods containing phytosterols have become available. These functional foods are in the form of margarines, spreads and salad dressings. In the case of most of these products, phytosterols are found esterified with long-chain fatty acids. These phytosterols are derived from soybean oil and are mainly beta-sitosterol, campesterol and stigmasterol.
Phytosterols are also known as plant sterols and, owing to their large sitosterol content, are sometimes called sitosterol. Phytosterols are virtually insoluble in aqueous media and are poorly soluble in lipid media. Esterification of phytosterols with long-chain fatty acids increases their lipid solubility.
ACTIONS AND PHARMACOLOGY
Phytosterols have cholesterol-lowering activity.
MECHANISM OF ACTION
The mechanism of the cholesterol-lowering activity of phytosterols is not fully understood. Phytosterols appear to inhibit the absorption of dietary cholesterol and the reabsorption (via the enterohepatic circulation) of endogenous cholesterol from the gastrointestinal tract. Consequently, the excretion of cholesterol in the feces leads to decreased serum levels of this sterol. Phytosterols do not appear to affect the absorption of bile acids.
It is believed that phytosterols displace cholesterol from bile salt micelles. Another proposed mechanism is the possible inhibition of the rate of cholesterol esterification in the intestinal mucosa.
Supplemental esterified phytosterols, following ingestion, undergo hydrolysis in the small intestine, catalyzed by such enzymes as cholesterol esterase, to yield the phytosterols beta-sitosterol, campesterol and stigmasterol. Of course, unesterified phytosterols do not undergo hydrolysis. About 5% of the ingested beta-sitosterol and about 15% of the campesterol are absorbed and transported via the portal circulation to the liver where some fraction of these phytosterols is glucuronidated. The phytosterols are excreted either in the free or glucuronidated form mainly via the biliary route.
INDICATIONS AND USAGE
Phytosterols may be indicated for the management of hypercholesterolemia.
Phytosterols have been compared with phytostanols to assess their relative efficacy in lowering total cholesterol and LDL-cholesterol. These studies confirm that both are effective in lowering these lipids. A recent review concluded that plant sterols and stanols, in the studies analyzed, reduce, on average, total cholesterol by 10% and LDL-cholesterol by 13%. They have no significant effect in either HDL-cholesterol or triglycerides.
CONTRAINDICATIONS, PRECAUTIONS, ADVERSE REACTIONS
Phytosterol supplementation is contraindicated in those with the rare genetic disorders sitosterolemia and cerebrotendinotic xanthomatosis.
Phytosterol supplementation should be avoided by pregnant women and nursing mothers.
Adverse reactions are mainly mild gastrointestinal ones, including occasional indigestion, feeling of fullness, gas, diarrhea and constipation. Phytosterol supplementation is generally well tolerated.
None known to date. Phytosterol supplementation may be additive to the cholesterol-lowering effects of such cholesterol-lowering drugs as the statins.
NUTRITIONAL SUPPLEMENTS AND FOOD
Some randomized trials have indicated that phytosterols may lower serum levels of alpha- and beta-carotene, lycopene and vitamin E, probably by interfering with their absorption. Neither vitamin A nor vitamin D levels appear to be affected by phytosterol ingestion. There are no data yet available on the effect of phytosterols on other carotenoids (lutein, zeaxanthin), flavonoids or polyphenols.
No reports of overdosage.
DOSAGE AND ADMINISTRATION
Phytosterols are cholesterol-like molecules found in all plant foods, with the highest concentrations occurring in vegetable oils. They are absorbed only in trace amounts but inhibit the absorption of intestinal cholesterol including recirculating endogenous biliary cholesterol, a key step in cholesterol elimination. Natural dietary intake varies from about 167-437 mg/day. Attempts to measure biological effects in feeding studies have been impeded by limited solubility in both water and fat. Esterification of phytosterols with long-chain fatty acids increases fat solubility by 10-fold and allows delivery of several grams daily in fatty foods such as margarine. A dose of 2 g/day as the ester reduces low density lipoprotein cholesterol by 10%, and little difference is observed between Delta(5)-sterols and 5alpha-reduced sterols (stanols). Phytosterols can also be dispersed in water after emulsification with lecithin and reduce cholesterol absorption when added to nonfat foods. In contrast to these supplementation studies, much less is known about the effect of low phytosterol levels in the natural diet. However, reduction of cholesterol absorption can be measured at a dose of only 150 mg during otherwise sterol-free test meals, suggesting that natural food phytosterols may be clinically important. Current literature suggests that phytosterols are safe when added to the diet, and measured absorption and plasma levels are very small. Increasing the aggregate amount of phytosterols consumed in a variety of foods may be an important way of reducing population cholesterol levels and preventing coronary heart disease.
Phytosterols are available in the form of fatty acid esters in some functional food products, including margarines, spreads and salad dressing. Unesterified phytosterols are available in capsules. Doses of the phytosterol esters range from 1.12 to 2.24 grams daily. Doses of the unesterified phytosterols are about 1 gram daily. Capsules, if used, should be taken with meals.
Foods Enriched with Plant Sterols and Plant Stanols
The majority of clinical trials that demonstrated a cholesterol-lowering effect used plant sterol or stanol esters solubilized in fat-containing foods, such as margarine or mayonnaise . More recent studies indicate that low-fat or even nonfat foods can effectively deliver plant sterols or stanols if they are adequately solubilized. Plant sterols or stanols added to low-fat yogurt , low-fat milk and orange juice have been reported to lower LDL cholesterol in controlled clinical trials. A variety of foods containing added plant sterols or stanols are available in Europe, Asia and the US, including margarines, mayonnaises, vegetable oils, salad dressings, yogurt, milk, soy milk, orange juice, snack bars and meats . Available research indicates that the maximum effective dose for lowering LDL cholesterol is about 2 g/d and the minimum effective dose is 0.8-1.0 g/d. In the majority of clinical trials that demonstrated a cholesterol-lowering effect, the daily dose of plant sterols or stanols was divided among two or three meals. However, consumption of the daily dose of plant sterols or stanols with a single meal has been found to lower LDL cholesterol in a few clinical trials.
Phytosterol supplements marketed as beta-sitosterol are available without a prescription in the US. Doses of 60-130 mg/d of beta-sitosterol have been found to alleviate the symptoms of BPH in a few clinical trials. Soft gel chews providing 0.5 g of plant stanols are being marketed for cholesterol-lowering at a recommended dose of 2 g/d. Phytosterol supplements should be taken with meals that contain fat.
In the US, plant sterols and stanols added to a variety of food products are generally recognized as safe (GRAS) by the FDA . Additionally, the Scientific Committee on Foods of the EU concluded that plant sterols and stanols added to various food products are safe for human use . However, the Committee recommended that intakes of plant sterols and stanols from food products should not exceed 3 g/d.
Few adverse effects have been associated with regular consumption of plant sterols or stanols for up to one year. People who consumed a plant sterol-enriched spread providing 1.6 g/d did not report any more adverse effects than those consuming a control spread for up to one year, and people consuming a plant stanol-enriched spread providing 1.8-2.6 g/d for one year did not report any adverse effects. Consumption of up to 8.6 g/d of phytosterols in margarine for 3-4 weeks was well-tolerated by healthy men and women, and did not adversely affect intestinal bacteria or female hormone levels. Although phytosterols are usually well-tolerated, nausea, indigestion, diarrhea and constipation have occasionally been reported.
Sitosterolemia, also known as phytosterolemia, is a very rare hereditary disease that results from inheriting a mutation in both copies of the ABCG5 or ABCG8 gene . Individuals who are homozygous for a mutation in either half transporter protein have dramatically elevated serum phytosterol concentrations due to increased intestinal absorption and decreased biliary excretion of phytosterols. Although serum cholesterol concentrations may be normal or only mildly elevated, individuals with sitosterolemia are at high risk for premature atherosclerosis. People with sitosterolemia should avoid foods or supplements with added plant sterols . Two studies have examined the effect of plant sterol consumption in heterozygous carriers of sitosterolemia, a more common condition. Consumption of 3 g/d of plant sterols for four weeks by two heterozygous carriers and consumption of 2.2 g/d of plant sterols for 6-12 weeks by 12 heterozygous carriers did not result in abnormally elevated serum phytosterols .
Pregnancy and Lactation
Plant sterols or stanols added to foods or supplements are not recommended for pregnant or breastfeeding women because their safety has not been studied. At present, there is no evidence that high dietary intakes of naturally occurring phytosterols, such as those consumed by vegetarian women, adversely affects pregnancy or lactation.
The LDL cholesterol lowering effects of plant sterols or stanols may be additive to those of HMG-CoA reductase inhibitors (statins). The results of controlled clinical trials suggest that consumption of 2-3 g/d of plant sterols or stanols by individuals on statin therapy may result in an additional 7-11% reduction in LDL cholesterol, an effect comparable to doubling the statin dose. Consumption of 4.5 g/d of stanol esters for eight weeks did not affect prothrombin times (INR) in patients on warfarin (Coumadin) for anticoagulation.
Fat-soluble Vitamins (vitamins A, D, E and K)
Because plant sterols and stanols decrease cholesterol absorption and serum LDL cholesterol concentrations, their effects on fat-soluble vitamin status have also been studied in clinical trials. Plasma vitamin A (retinol) concentrations were not affected by plant stanol or sterol ester consumption for up to one year. Although the majority of studies found no changes in plasma vitamin D (25-hydroxyvitamin D3) concentrations, one study observed a small (7%) but statistically significant decrease in plasma 25-hydroxyvitamin D3 concentrations at the end of one year in those who consumed 1.6 g/d of sterol esters compared to placebo. There is little evidence that plant sterol or stanol consumption adversely affects vitamin K status. Consumption of 1.6 g/d of sterol esters for six months was associated with a nonsignificant 14% decrease in plasma vitamin K1 concentrations, but carboxylated osteocalcin, a functional indicator of vitamin K status, was unaffected. In other studies of shorter duration, consumption of plant sterol and stanol esters did not significantly change plasma concentrations of vitamin K1 (89) or vitamin K-dependent clotting factors. Consumption of plant sterol or stanol-enriched foods has been found to decrease plasma vitamin E (alpha-tocopherol) concentrations in a number of studies. However, those decreases generally do not persist when plasma alpha-tocopherol concentrations are standardized to LDL cholesterol concentrations. This suggests that observed reductions in plasma alpha-tocopherol are due in part to reductions in its carrier lipoprotein, LDL. In general, consumption of plant sterol and stanol-enriched foods at doses of 1.5 g/d or more have not been found to have adverse effects on fat-soluble vitamin status in well-nourished populations.
Dietary carotenoids are fat-soluble phytochemicals that circulate in lipoproteins. A number of studies have observed 10-20% reductions in plasma carotenoids after short-term and long-term consumption of plant sterol- or stanol-enriched foods. Even when standardized to serum total or LDL cholesterol concentrations, decreases in alpha-carotene, beta-carotene and lycopene may persist, suggesting that phytosterols can inhibit the absorption of these carotenoids. It is not clear whether reductions in plasma carotenoid concentrations confer any health risks, but several studies have found that increasing intakes of carotenoid-rich fruits and vegetables can prevent phytosterol-induced decreases in plasma carotenoids. In one case, advice to consume five daily servings of fruits and vegetables, including one serving of carotenoid-rich vegetables, was enough to maintain plasma carotenoid levels in people consuming 2.5 g/d of plant sterol or stanol esters.
Although relatively safe, long-term use of increased phytosterol intake has not been studied.
Those who are pregnant/lactating or have a cholesterol condition, especially, should seek the advise of a healthcare professional.
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