Plant stanols are part of a larger group of compounds found in plants called phytosterols. Also included in this group are compounds called plant sterols, which have a slightly different structure. Think of phytosterols as the "cholesterol of plants;" both plant stanols and plant sterols have structures similar to the cholesterol in human bodies. Scientists have been studying these compounds since the 1950s, when they discovered that phytosterols might reduce cholesterol levels.
Mechanism of Action
Research suggests that phytosterols block your body's absorption of cholesterol from the foods you eat. Cholesterol normally binds to fat absorption molecules, called micelles, within your gastrointestinal tract. But when plant stanols and sterols are also present, they take the place of cholesterol in micelles because of their similar shape. The end result: Less cholesterol is absorbed.
Additional Mechanisms
Scientists suspect that additional mechanisms also might be responsible for lowering blood cholesterol. Phytosterols could affect cholesterol metabolism within the cells of the intestine, drawing in more of the cholesterol from the bloodstream so less is floating around. But further study is necessary to fully understand the processes leading to lower cholesterol levels.
Recommendations
The National Cholesterol Education Program's most recent guidelines advise consuming 2 grams of plant stanols a day for people with high cholesterol levels. This is part of the "therapeutic lifestyle changes" for reducing the risk of heart disease along with reductions in fat intake, increases in fiber and physical activity. If you already take cholesterol-lowering medications, such Lipitor or other statins, phytosterols might reduce your cholesterol levels even further.
Foods With Plant Stanols
Though phytosterols are naturally present in plant-based foods, such as vegetables, nuts and seeds, Americans typically do not consume enough to reduce cholesterol levels. But phytosterols are now available in a slightly modified form--plant stanol esters and plant sterol esters--in some fortified margarine spreads. Two daily servings of these margarines should provide enough plant stanols or sterols to bring down blood cholesterol levels.
Safety
People in Finland have been using plant stanols for more than 10 years with no reported complications. Additionally, in the American Journal of Cardiology, J. Plat and R.P. Mensink reviewed numerous studies establishing the safety and effectiveness of plant stanols and sterols in foods. However, they noted that blood levels of carotenes--antioxidants that also serve as the building blocks of vitamin A--decrease when people use spreads containing phytosterols. If you decide to use such a spread, make sure to get additional carotene from brightly colored fruits and vegetables.
A more serious downside is that blood levels of plant sterols increase when you consume phytosterols. The effects of high plant sterol levels in the blood are not yet known. However, another disorder which causes high sterol levels in the blood--sitosterolemia--is associated with an increased risk of both heart disease and anemia. Still, Plat and Mensink emphasize that this association has not been proved for phytosterols, and they consider phytosterols safe to use.
References
- The American Journal of Cardiology; Plant Stanol and Sterol Esters in the Control of Blood Cholesterol Levels: Mechanism and Safety Aspects; J. Plat and R.P. Mensink; July 2005
- National Heart, Lung and Blood Institute: Detection, Evaluation and Treatment of High Blood Cholesterol in Adults
