Plant sterols are essential components of plant cell membranes and are structurally similar to cholesterol found in our bodies. Sterols are present in small quantities in fruits, vegetables, nuts, seeds and legumes. The efficacy of plant sterols in lowering blood cholesterol levels was observed in the 1950s, according to Pollak OJ, in an article on the Reduction of Blood Cholesterol in Man, published in the American Heart Association (AHA) journal. As plant sterols are not water-soluble and hence not wholly absorbed by our bodies, they are added to foods like margarine, after first being extracted from soybean oil or pine tree oil. Consumption of plant sterols can have both positive and negative effects on cholesterol levels.
A high blood cholesterol level, especially an increase in low density lipoprotein (LDL), the so-called bad cholesterol, raises one's risk of coronary heart disease (CHD). Studies have proven that an intake of 1-3 grams of plant sterols reduces LDL. The European Food Information Council (EUFIC) website quotes epidemiological data which estimates that a 10 per cent reduction in LDL cholesterol can lower one's lifetime CHD risk by 20 per cent.
Even though plant sterols are not properly absorbed by human intestines, plant sterols effectively reduce cholesterol absorption and lower the circulation levels of cholesterol. According to the American Journal of Clinical Nutrition, a reduced absorption of cholesterol, through an intake of plant sterols, leads to a decrease in plasma and LDL-cholesterol concentrations.
Individuals who suffer from sitosterolemia, a lipid metabolic disorder, absorb and store an abnormally high amount of plant sterols. They also experience biliary excretion of dietary sterols, have high cholesterol levels and develop premature coronary atherosclerosis. These individuals have a high mortality rate and should maintain a diet that is restricted in plant sterols.
A study entitled "Stanol/Sterol Ester-Containing Foods and Blood Cholesterol Levels," published in the AHA journal, observed decreased levels of plasma alpha and beta carotene, -tocopherol, and lycopene, resulting from the consumption of foods containing plant sterols. However, this plasma carotenoid deficiency can be overcome by consuming a carotene-rich diet that contains dark green, yellow and orange fruits and vegetables.
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