The Role of Phytosterols in Reducing Cholesterol
Plant Sterols in "Functional Foods" may be Too Much of a Good Thing
Unlike animal cells, plants do not usually synthesize substantial cholesterol. Instead, they create a variety of phytosterols to serve in the stabilization of cell membranes and creation of hormones. These share a similar structure to cholesterol with only an addition of a side chain methyl or ethyl group at Carbon 24 of the molecule.
Phystosterols are a general term for related plant sterols and stanols. Plant sterols have a double-bond in their structure while stanols are saturated forms. Some phytosterols are unique to a specific plant species while others are ubiquitous spanning plant families. The most commonly encountered phytosterols are beta-sitosterol, campesterol, and stigmasterol.
High levels of phytosterols are expected in oils, seeds, nuts, and fatty vegetables. Significant levels are found in many fruits and vegetables. Since phytosterols are increasing with demand, some manufacturers are resorting to materials derived from a by-product of the paper industry called “tall oil.” This is touted as “non-GMO” -apparently to make it more palatable to the more sophisticated health food consumer. Manufacturers also modify phytosterols by connecting them (esterifying) with fatty acids so they can be blended readily into foods.
Phytosterols and Cholesterol Reduction
While Phytosterols often have novel pharmacological effects, some have recently become popular as an emerging natural way to lower cholesterol. Moderate intake of phytosterols is associated with a 10-15% reduction. It appears that cholesterol lowering effects occur with the inclusion of 1 gram phytosterols per day and level off at levels approaching 3. Taking more than 3 grams a day has no advantage and may be detrimental. In contrast, the normal Western diet includes about 200-300 mg of phytosterols. The United States Food and Drug Administration (FDA) has approved the claim that foods enriched with 1.3 grams of plant sterol esters or 3.4 grams of stanol esters “may reduce the risk of heart disease.”
Ways that phytosterols reduce serum cholesterol:
- Compete with cholesterol for absorption in the small intestine
- Alter cholesterol creation in the liver
- Increase bile-salt excretion and block its reabsorption
Challenges Regarding Enriched Foods
While a diet rich in natural phytosterols is a desirable thing, building concern exists regarding excessive intake from enriched sources like “functional foods.” Emerging research is alluding that these added sterols may be incorporated into atherosclerotic plaques much like conventional cholesterol.
European Concerns
Several European countries have voiced concern regarding the lack of long term safety assurance coupled with correlations of cardiovascular disease. Countries like Germany are also concerned about the additive effect of consuming several different products and recommend a daily intake of less than 3 grams a day. There is also a sense of bewilderment regarding how this material was able to achieve the relatively rare claim status by the FDA without long term efficacy and safety.
Toxicity
Since these materials may inhibit absorption of beta carotene and fat soluble vitamins, children and women breastfeeding are discouraged from use. Those with a rare autosomal recessive condition (phytosterolemia) should make it a point to avoid plant sterols since they tend towards severely elevated levels in the tissues.
Additional References
Patel SB, Zablocki CJ. "Plant Sterols and Stanols: Their Role in Health and Disease". J Clin Lipidol. . 2008 Apr ;2(2):S11–S19.
Weingartner O, Bohm M, Laufs U. "Controversial role of plant sterol esters in the management of hypercholesterolaemia"Eur Heart J. 2009 Feb 2;30(4):404-409.
Olive oil is high in beta-sitosterol
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