Phytosterols, also known as plant sterols, are cholesterol-like molecules found in plants, such as whole grains, fruits, legumes, and vegetables. All plants contain phytosterols but, to date, the amount of sterols contained in each plant has not been established. Although there have been more than 40 types of plant sterols discovered so far, three of them are the most abundant: beta-sitosterol, campesterol, and stigmasterol.
Phytosterols differ from animal cholesterol only slightly in their structure, but vary greatly in their ability to induce atherosclerosis, which is the buildup of a fatty plaque on vessels that can lead to heart disease.
Animal Cholesterol Bad, Phytosterols Good
In persistently high amounts, the cholesterol found in animals can increase blood cholesterol and may lead the development of atherosclerosis and heart disease.
Phytosterols, on the other hand, are minimally absorbed from the small intestine, so they do not enter the bloodstream. Additionally, phytosterols stop or slow absorption of dietary cholesterol and cholesterol made by the liver. How this occurs is not fully known. Nonetheless, there have been many products that have hit the grocery shelves containing phytosterols, such as margarine spreads, salad dressings and supplements. Many of these products may contain saturated phytosterols, which are known as phytostanols, or plant stanols.
Do Phytosterols Really Lower Cholesterol?
There have been many studies that have examined the cholesterol-lowering abilities of phytosterols. Several studies have indicated that up to two grams of phytosterols per day can lower low-density lipoproteins (LDL) by 10 percent. This amount would roughly equal to 1 teaspoon of the extract, or one tablespoon of a spread containing phytosterols.
High-density lipoproteins (HDL) and triglycerides do not appear to be affected by phytosterols. Additionally, it only takes one to two weeks to see the cholesterol-lowering results of phytosterols. During these studies, individuals were either placed on a low fat diet or maintained the diet they had before the study. The Food and Drug Administration has taken notice and has allowed products containing phytosterols to be labeled as “heart-healthy”. There are many products currently on the market, such as salad dressings, spreads, candies, and supplements and this designation would be clearly labeled on any product containing sterols or stanols.
Despite the wide variety of foods stanols are contained, there is some debate on the effectiveness of stanols when taken as a supplement. Some researchers contend that, when purified during the manufacturing process, the phytosterols found in supplements are not biologically active. This would mean that the phytosterols found in some supplements may not be effective in lowering cholesterol if not properly prepared by the manufacturer. The phytosterols found in foods, from soybeans to spreads, are biologically active and would therefore be beneficial in lowering cholesterol.
The Bottom Line
Eating fruits and vegetable is good for you, and the research mentioned above is just further evidence of that.
Also, although these results appear promising, there is still more information needed to address the potential for phytosterols to cause atherosclerosis when used long-term in humans. The research to date indicates that phytosterols may actually reduce the likelihood of atherosclerosis development in healthy individuals. The exception for this would be individuals who suffered from the rare, genetic condition, phytosterolemia, or sitosterolemia, which causes high levels of phytosterols in the blood and premature atherosclerosis.Sources:
Ostund RE. Phytosterols, cholesterol absorption and healthy diets. Lipids. e-pub 9 January 2007
Ostund RE. Phytosterols and cholesterol metabolism. Curr Opin Lipidol. 2004 Feb;15(1):37-41.
Pinedo S, Vissers M et al. Plasma levels of plant sterols and the risk of coronary artery disease: the prospective EPIC-Norfolk Population Study. Journal of Lipid Research, Vol. 48, 139-144, January 2007.
Saji J, AV Sorokin, PD Thompson. Phytosterols and vascular disease. Current Opinion in Lipidology. 18(1):35-40, February 2007.