Plant sterols, also known as phytosterols, are naturally occurring compounds found in plants that have a chemical structure similar to cholesterol. When consumed, they compete with cholesterol for absorption in the gut, which can help lower LDL ('bad') cholesterol levels. For this reason, they are often added to fortified foods like margarine, yogurt, and milk products. However, while generally safe, there are specific side effects and situations where their use requires caution.
Common Mild Side Effects
For the majority of the population, any adverse effects from consuming plant sterols are mild and primarily affect the gastrointestinal system. These symptoms are typically transient and may resolve as the body adjusts.
- Digestive Discomfort: Some individuals report mild digestive upset, which can include diarrhea, constipation, or flatulence. A phenomenon known as 'fat in the stool' (steatorrhea) can also occur.
- Nausea: In some cases, people may experience feelings of nausea or indigestion.
Interference with Nutrient Absorption
One well-documented effect of plant sterol intake is the potential to interfere with the absorption of certain fat-soluble nutrients. This is due to their mechanism of action, which involves blocking the intestinal absorption of fats.
- Reduced Carotenoid Levels: Studies have shown that consuming plant sterols can slightly reduce blood concentrations of carotenoids, particularly beta-carotene. However, this reduction is generally considered small and not clinically significant, especially if sufficient amounts of carotenoid-rich fruits and vegetables are consumed.
- Other Fat-Soluble Vitamins: While some reports suggest minor effects on other fat-soluble vitamins, such as vitamin E, most research indicates that levels of vitamins A and D are not meaningfully affected when expressed in relation to lipid levels.
Who Should Avoid Plant Sterols?
The Serious Risk of Sitosterolemia
By far the most significant negative side effect is the exacerbation of a rare genetic disorder called sitosterolemia. This condition, caused by mutations in the ABCG5 or ABCG8 genes, results in the body absorbing excessively high amounts of plant sterols into the bloodstream.
- Premature Atherosclerosis: The buildup of these fatty substances in the arteries can lead to premature and severe atherosclerosis, significantly increasing the risk of cardiovascular events like heart attack and stroke from a young age.
- Xanthomas: Sufferers often develop xanthomas, which are yellowish growths of accumulated lipids on or under the skin, typically around joints and tendons.
- Blood Abnormalities: Some individuals with sitosterolemia may also experience hemolytic anemia, where red blood cells are prematurely destroyed.
Other Vulnerable Groups
- Pregnant and Breastfeeding Women: Due to a lack of sufficient long-term safety data, plant sterols are not recommended for pregnant or breastfeeding women.
- Children Under 5: Similarly, there is limited information on the safety and specific nutritional needs of young children, so foods fortified with plant sterols should be avoided for this age group.
- Short Bowel Syndrome: Caution is advised for those with short bowel syndrome, as a case report noted potential worsening of liver function.
Plant Sterols and Drug Interactions
Plant sterols are generally considered safe to use alongside many medications, but it is important to be aware of how they might affect specific cholesterol-lowering drugs.
| Interaction Aspect | With Statins (e.g., atorvastatin) | With Ezetimibe (Zetia) |
|---|---|---|
| Mechanism of Action | Different: Statins inhibit cholesterol production in the liver. | Similar: Ezetimibe blocks cholesterol absorption in the gut. |
| Combined Effect | Additive: Taking plant sterols can further enhance the LDL-lowering effect of statins. | Little to no additional benefit: Both work similarly and may not offer an additive effect. |
Potential Long-Term and Minor Concerns
While long-term safety studies have shown no significant adverse effects for the healthy population at recommended intakes, some minor and largely theoretical concerns have been raised. Animal studies have shown some effects, but these haven't been replicated in humans at typical doses. For instance, a mouse study found that plant sterol esters caused greater weight gain and adversely affected gut microbiota compared to oat beta-glucans, but human relevance is still unclear.
Conclusion
For the vast majority of healthy adults seeking to manage their cholesterol, plant sterols present a safe and effective dietary tool when consumed in recommended amounts. The potential negative side effects of plant sterols are mostly limited to mild, temporary digestive issues and a minor reduction in carotenoid absorption, which is easily managed with a balanced diet rich in fruits and vegetables. The most serious risk is confined to individuals with the rare genetic disorder sitosterolemia, who must avoid these compounds. As with any dietary change or supplement, consulting a healthcare provider or dietitian is a crucial first step, especially for those in a vulnerable group or those taking prescription medications.
For more in-depth information, the Cleveland Clinic offers a comprehensive guide on plant sterols.
