Health benefits of dietary phytosterols

Phytosterols are steroid alcohols (triterpenes). Phytosterols (plant sterols and stanols, saturated form of the sterol) are chemically like cholesterol molecules. Phytosterols are related to cyclopentaphenanthrene with four condensed rings of 28 or 29 carbons. Phytosterols present a diverse group of more than 200 different compounds found in various plant and marine materials. They are essential structural components of the plant cells and membranes. Phytosterols regulate membrane fluidity of plant cells. Sitosterol, campesterol and stigmosterol are the most abundant phytosterols in plants. Stanols such as sitostanol, and campestanol are saturated plant sterols. Phytosterols can be converted into phytostanols by chemical hydrogenation. Phytosterols are not synthesized by the body and an estimated 200-300 mg phytosterol is obtained daily from the diet. In humans, intestinal absorption of Phytosterols is low (0-10%) compared to the >40% for cholesterol. The phytosterols and stanols are naturally occur in a variety of foods such as nuts, vegetable oils, seeds and cereals. The prime function of phytosterols is to inhibit the intestinal absorption of cholesterol. Human body uses the Phytosterols to produce the hormones it needs. Phytosterols are not synthesized in human body, are poorly absorbed and are excreted faster from the liver than cholesterol.

Definitions

Phytosterols encompass plant sterols and stanols, are steroid compounds similar to cholesterol which occur in plants and vary only in carbon side chains and/or presence or absence of a double bond. Stanols are saturated sterols, having no double bonds in the sterol ring structure (Wickipedia.org).

Phytosterols are plant –derived compounds that are structurally similar to cholesterol. The compounds may lower blood cholesterol levels, particularly LDL cholesterol and may have uses as immunostimulants and in treating benign prostate enlargement.

Phytosterols and cholesterol

1. Phytosterols are not synthesized in the human body.
2. Phytosterols have their intestinal absorption much lower than that of cholesterol and
3. Large doses of Phytosterols in diet diminish the absorption of cholesterol.

Mechanism of action of phytosterols

Cholesterol absorption is a very important physiological mechanism that regulates cholesterol metabolism. Phytosterols have been shown to inhibit the uptake of both dietary and endogenously produced (biliary) cholesterol from intestinal cells. Such inhibition results in a decrease in serum total and LDL-cholesterol levels. Levels of HDL – cholesterol and triglycerides do not appear to be affected by dietary phytosterol consumption (AbuMweis et al 2008).

Food sources

Plant sterols are found in all foods of plant origin. Foods rich in phytosterols include unrefined vegetable oils, whole grains, nuts and legumes. The main sources of Phytosterols are vegetable oils, vegetable fat spreads and margarines, cereals and cereal products (bread) and vegetables. These sources contribute to 50-80% of the total phytosterol intake (Klingberg et al 2008,Valsta et al 2004). The fruits contain about 12% of phytosterol. The content of phytosterols in most vegetable oils ranges from 1.0 to 5.0 mg/g of oil. Wheat germ oil contains 17-26 mg/g of phytosterols. Lower amounts of phytosterols are found in palm oil (0.7 – 0.8 mg/g ), coconut oil (0.7 -0.8mg/g ), and olive oil (1.4 – 1.9 mg/g ). The phytosterol content in Finland rye, wheat, barley and oat are 1.0, 0.7,0.8 and 0.4 mg/g respectively.

Health promoting properties

The most important function of phytosterols is their plasma cholesterol –lowering effect through inhibition of intestinal cholesterol absorption and enhanced elimination of cholesterol in stools. Maximum cholesterol – lowering benefit is achieved at doses of 2-3 g/day (Hallikainen et al 2000, Jones et al 2000, Maki et al 2001). Several recent studies indicate that the consumption of 2g/day of sterols or stanols could result in a reduction in the risk of heart diseases by about 25% (Law 2000, Jones and Raeini – Sarjaz 2001, Hicks and Moreau 2001). The potential health effects of phytosterols include the prevention of inflammation caused by rheumatoid arthritis, control of blood sugar in diabetes, the reduction of the risk of various types of cancers and the prevention of inflammation caused by atheroscelerosis. Phytosterols protect against colon cancer by slowing down the reproduction of cells in the large intestine.  The phytosterols have been shown to effectively reduce prostatic hyperplasia (Berges et al 1995, Berges, Kassen and Senge 2000) and colon cancer (Bouie and Lamprecht 1999). The phytosterols have limited antioxidant activity.

Recommended dietary intakes

Dietary phytosterol intakes have been estimated to range approximately 150 mg/day to 450 mg/day in various populations. Early human diets were rich in phytosterols providing as much as 1 g/day. On average, most Americans get between 2 and 4 mg/day of the phytosterols. Natural health practitioners believe that we actually need to consume between 30 and 50 mg/day of phytosterols. The United States Food and Drug Administration (FDA) recommended an amount of 800 mg of phytosterol per day on a consistent basis for increased health benefits.  Typical consumption of plant sterols in the diet is approximately 200-400 mg/day (Aparna Kuna et al 2011).

Functional use of  dietary phytosterols 

Phytosterols and phytostanols in free or esterified form are added to foods for their properties to reduce absorption of cholesterol in the gut and thereby lower blood cholesterol levels. Phytosterols are currently added as an esterified form to wide range of food products such as margarines, yoghurts, salad dressings, milk and snack bars. Phytosterol and phytostanol esters are used as a fat replacer in margarines and spreads. These esters can provide a crispy texture (prevents sogginess) to cereal products by coating the product surface. Both phytosterol and phytostanol esters give an enhanced creamy texture to low fat dairy products (yoghurt / drinking yoghurt). They may also improve the taste of food products by masking bitterness and hence reduce the amount of sugar or sweetener required to obtain a pleasant taste and mouth feel (e.g. soy drinks).The phytostanol and phytosterol esters are microbiologically inert during the fermentation process used to produce yoghurt. The phytostanol and phytosterol esters added to various food products show excellent stability at different pH levels during long term storage (upto one year). The phytostanol and phytosterol esters are also stable in milk and fermented milk products with viable bacteria like yoghurts and yoghurt drinks.
                Dietary intake of phytosterols lowers the absorption of cholesterol