• Plant sterols are structurally similar to cholesterol and are often called phytosterols.
• More than 40 sterols have been identified in plants, of which b-sitosterol, campesterol and stigmasterol are the most abundant.
• Stanols are saturated sterols and have no double bond in the ring structure.
• The average daily intake of phytosterol from the diet is ~250 mg/day, while that of stanol is ~25 mg/day.
• To make plant sterol more soluble, sterols are hydrogenated, forming stanols.
• More than 30 clinical studies have shown that plant sterols and stanols may lower total plasma cholesterol concentrations.
• The FDA has approved 'health claims' on plant sterol and stanol products. The possible claim is that phytosterols may maintain healthy cholesterol with a low fat diet.
• b-sitosterol is the most abundant phytosterol, comprising 50% of dietary phytosterols.
• Sterols and stanols are equally effective in lowering total plasma cholesterol concentrations.

• Plant sterols are poorly absorbed. In the case of sitosterol, only 5% is absorbed.
• Plant sterols decrease total serum cholesterol and LDL cholesterol concentrations in a dose dependent manner, but not serum HDL cholesterol.
• The mechanism by which plant sterols lower cholesterol has not been fully determined. The following theories have been proposed.
  • Compete efficiently with dietary cholesterol for micelle incorporation
  • Reduce cholesterol transport across the unstirred water layer in gastrointestinal tract
  • Inhibit cholesterol esterification in enterocytes
• Since plant sterols and stanols may alter micelle formation, it is possible that absorption of fat-soluble nutrients (such as vitamin E and carotenoids) is diminished.
• b-sitosterol may suppress tumor cell growth.

• No health hazards or side effects are known.
• Caution with pregnancy or nursing, consult physician before using.

1. spreads and dressings for salad containing at least 0.65 grams of plant sterol esters per serving,
2. spreads, dressings for salad, snack bars, and dietary supplements in softgel form containing at least 1.7 grams plant stanol esters per serving.  [~20~]

There has been conflicting evidence on the consumption of plant sterols/stanols and their effect on plasma fat-soluble vitamin and carotenoid concentrations:

One study compared the consumption of plant sterol/stanol esters on serum fat-soluble vitamin and carotenoid concentrations. Fifteen subjects were randomly fed a diet containing either margarine (control), margarine with sterol esters (1.92 grams/day), or margarine with stanol esters (1.76 grams/day) over 21 days. No significant differences were found in initial or final serum concentrations of fat-soluble vitamins or carotenoids among the 3 phases. These results suggest that consumption of esterified plant sterols or stanols does not effect fat-soluble vitamin or carotenoid concentrations when compared to a control diet. [~21~]

Forty-six subjects with hypercholesterolemia consumed a sterol-free spread (control), a sterol ester spread (2.3 grams) and a stanol ester spread (2.5 grams). With each treatment, subjects were advised to eat 5 or more servings of fruits and vegetables, and one or more the servings was to be carrots, sweet potatoes, pumpkin, tomatoes, apricots, spinach or broccoli. Adding 1 daily serving of vitamin A-rich fruit or vegetable while consuming plant sterol or stanols esters, allowed subjects to maintain normal plasma carotenoid concentrations. Thus, it is recommended for individuals to consume an additional serving of a carotenoid-containing fruit or vegetable when consuming plant sterol or stanol products. [~22~]

A recent mini-review discusses how regular consumption of plant sterols/stanols may result in a 10-20% decrease in plasma carotenoid concentrations. Although it is believed that there is no health risk associated with slight decrease in blood concentrations of carotenoids due to intake of plant sterol/stanols, the mechanism of how plant sterols/stanols affect plasma carotenoid concentrations is unclear. Data on carotenoids was pooled from 2 studies on plant sterols. Plasma carotenoid concentrations were presented as tertile values, showing that subjects with the lowest plasma carotenoid concentrations had the least decrease in their plasma alpha-, beta-carotene and lycopene levels. The mid and high-tertile subjects demonstrated a higher decrease in alpha and beta-carotene concentrations, more so than the lowest tertile group. However, the plasma levels of carotenoids in the mid and high tertile groups did not reach the level found in the low tertile group. The same was found for lycopene. From this, the importance of variability in baseline carotenoid levels among subjects was highlighted. Numerous factors affect plasma carotenoid levels (dietary habits, vegetable/fruit intake, seasonal variation (10-40%), bioavailability of carotenoids, etc.) [~23~]

A one-year, randomized, double-blind study was conducted using placebo and either 1.8 or 2.6 g of sitostanol per day as margarine. The result showed that margarine containing stanols significantly lowered serum total and LDL cholesterol concentrations compared to placebo. Although no difference was found for the first 6 months between the 1.8 g and 2.6 g sitostanol groups, higher amounts of sitostanol in margarine (2.6 g) showed slightly but significantly greater decrease between 6 and 12 months of study. ⁸

A double-blind study with 55 hypercholesterolemic subjects for 8 weeks was conducted to see if plant stanols decrease serum cholesterol concentrations using two different sources of stanols. Plant stanols were derived from soy oil or wood. The stanol composition in wood and vegetable oil was 2.15 g and 0.19 or 1.50 g and .07 g of sitostanol and campestanol, respectively. The basic diet was low fat (25 – 26% of energy) during the experiment. The reduction in serum total cholesterol concentrations was 10.6% and 8.1% greater than in the control group. The same trend was observed on serum LDL cholesterol concentrations. Results suggested that plant stanol esters with a low fat diet can diminish serum cholesterol concentrations. ⁹

In one study with healthy or mildly hypercholesterolemic subjects, three different levels of plant sterol margarine spreads were given to see the effect on blood lipid and fat-soluble nutrients. Plant sterols at the level of 0.83, 1.61 and 3.24 g/day or placebo were fed for 3.5 weeks. Compared to the control spreads, total serum cholesterol concentration significantly decreased by 0.26 – 0.35 mmol/L for the 3 plant sterol groups. However, there was no difference of cholsterol-lowering action among sterol groups. Lipid standardized carotene concentrations were decreased by 0.83 and 3.24 g plant sterols. The author concluded that daily ingestion of 1.6 g plant sterols may favorably influence serum cholesterol concentrations. ¹⁰

In a review paper, Law found the reduction of serum LDL cholesterol concentration was significantly greater in old people than in young people. Plant sterols or stanols decreased serum LDL cholesterol concentrations in a dose-dependent manner up to 2 g/day. ¹¹

Prostate Cancer: An animal study was done to examine the effect of phytosterols (PS) versus cholesterol on the growth and metastasis of the PC-3 human prostate cancer cells in SCID mice. The SCID mice were fed a diet containing 2% of either a PS mixture or cholesterol plus 0.2% cholic acid, and implanted with 2x10(6) tumour cells per mouse. The experimental diet consisted of 39.7% cornstarch, 20% casein, 13.2% maltodextrin, 10% sucrose, 7% soybean oil, 5% cellulose, 3.5% mineral mix, 1% vitamin mix, 0.3% L-cystine, 0.25% choline bitartrate and 0.0014% t-butylhydroquinone. Diets were supplemented with 0.2% cholic acid plus 2% of either cholesterol (control diet) or PS mixture. Tumour growth was monitored for 8 weeks post inoculation, and animals fed the PS diet had tumours 40-43% smaller than those fed the cholesterol diet. The number of mice with lymph node and lung metastasis was almost one-half that of cholesterol-fed group. In addition, an analysis of the growth and migration of these cancer cells in vitro was conducted. Results found that both beta-sitosterol and campesterol inhibited the growth of PC-3 cells by 70 % and 14%, respectively, while cholesterol supplementation increased growth by 18% when compared with controls. PS taken as a dietary supplement can indirectly inhibit the growth and metastasis of PC-3 cells, and PS directly (in tissue culture media) inhibited the growth and metastasis of PC-3 cells. [~24~]

In a randomized, double-blind, placebo-controlled multicenter study, 200 subjects with symptomatic benign prostatic hyperplasia were given 20 mg b-sitosterol three times a day for 6 months. Treatment with plant sterol significantly lowered modified Boyarsky scores as compared to the placebo group. The peak of urine flow was improved while mean residual urinary volume decreased. Prostatic volume was not influenced in either group.¹²

Stomach Cancer: An epidemiological study in Uruguay showed there was a strong inverse relationship between total phytosterol intake and stomach cancer in a dose response effect. This risk of association remained similar after adjustment for vegetables, fruits and other nutrients. Furthermore, when combined, b-sitosterol and a-carotene showed stronger inverse association with risk of stomach cancer. A similar inverse relationship was epidemiologically observed in lung cancer.^{13 14}

• To reduce serum cholesterol, 1.5 - 3.0 g of plant sterols or stanols should be taken daily.^{1 2}
• Regardless of the origin of sterols or saturation of sterols (phytosterol or phytostanol), hypocholesterolemic action has been found.³