How do plant sterols work?
Sterols are the equivalent of animal cholesterol in the vegetable world. In fact, these substances so closely resemble cholesterol that they compete for the same receptors in the small intestine. Eating foods containing plant sterols, or taking supplements, can therefore block cholesterol absorption into the circulation to help reduce your cholesterol levels.
The cholesterol in your bloodstream comes from two main sources - that which you make in your liver (around 800mg per day) and that absorbed from your diet (typically around 300mg per day). Some of the cholesterol made in your liver is also delivered into the intestines via the bile from which it is then reabsorbed into your circulation.
Plant sterols therefore block the absorption not just of dietary cholesterol but also of the cholesterol that is recycled from the bile. As a result, more cholesterol is voided via the bowels, along with most of the plant sterols. A large trial involving over 22,500 men and women living in Norfolk showed that people with the highest dietary intake of plant sterols have the lowest cholesterol levels, for example.1
Benefits of plant sterols
The EU has reviewed all the evidence and has authorised the nutrition and health claims that plant sterols can lower blood cholesterol levels by:
- 7% to 10% at a daily intake of 1.5g to 2.4g plant sterols per day
- 10% to 12% with a daily intake of 2.5g to 3g per day
These effects are seen with 2 to 3 weeks of daily use.
The protective effects appear to be even more pronounced in people with type 2 diabetes. For example, one study showed they reduced LDL-cholesterol levels by 26.8% in people with type 2 diabetes, compared to a reduction of 15.1% in those without diabetes.2
By improving your cholesterol levels, following a sterol-enriched diet may help to reduce your risk of cardiovascular diseases such as hardening and furring up of the arteries, high blood pressure, heart attack and stroke.3 As a result, there is also an approved EU claim that a dose of 1.5g to 3g of plant sterols and plant stanol esters has been shown to lower/reduce blood cholesterol. High cholesterol is a risk factor in the development of coronary heart disease.
Supplement or food?
Although diet should always come first, it's difficult to obtain optimum amounts of sterols from food sources alone. The average omnivore diet provides 200mg - 400mg sterols per day, while following a vegetarian diet can provide up to 800mg per day.
In the Norfolk study mentioned above, for example, those with the lowest sterol intake obtained an average of just 178mg daily, while those with the highest intakes obtained an average of 463mg per day. For optimum benefits, intakes of at least 2g to 3g per day are needed. In addition, sterols in plant foods are naturally bound to fibre, which limits their action, unlike those found in supplements which are more available to the body.
As well as eating a diet that favours healthy oils, nuts, seeds, fruit and vegetables, taking a plant sterol supplement is a useful alternative solution for people with a moderately raised cholesterol who are unable or unwilling to take statins. Fortified foods such as yogurts and spreads that contain plant sterols or stanols are also available.
Plant sterols vs statins
Statins are the medical treatment of choice for lowering cholesterol levels. These drugs work by inhibiting a liver enzyme (HMG-CoA reductase) so that less new cholesterol is made and pushed out into your circulation. Because plant sterols work in a different way to statins, the two can be combined to lower cholesterol levels through a two-pronged approach.4 In fact, adding sterols to statin medication is more effective than doubling the statin dose.5 The combination of a statin plus a plant sterol supplement can therefore help to reduce the dose of statin needed, which may reduce the risk of statin side effects (such as muscle aches and fatigue). Do check with your doctor before taking plant sterols, however, and never stop taking any medication without seeking medical advice.
Plant sterol dose
The optimum dose is 2g to 2.4g plant sterols per day. Do not take more than 3 grams per day in the form of supplements as there is no evidence of additional health benefits from taking larger amounts, and there is a possibility that higher doses may reduce the absorption of some fat-soluble vitamins and carotenoids (antioxidant plant pigments).6
Plant sterols side effects
No significant side effects have been reported when taking plant sterol supplements. A few people notice diarrhoea or fat in their motions. If this happens, reduce the dose of plant sterols and the amount of fat in your diet.
Plant sterols have been approved by the European Union Scientific Committee as safe for inclusion in functional foods.
1Andersson SW et al (2004). Intake of dietary plant sterols is inversely related to serum cholesterol concentration in men and women in the EPIC Norfolk population: a cross-sectional study, Eur J Clin Nutr 58(10):1378-85
2Lau VW et al (2005). Plant sterols are efficacious in lowering plasma LDL and non-HDL cholesterol in hypercholesterolemic type 2 diabetic and nondiabetic persons, Am J Clin Nutr 81(6):1351-8
3Patch CS et al (2006). Plant sterols as dietary adjuvants in the reduction of cardiovascular risk: theory and evidence, Vasc Health Risk Manag 2(2):157-62
4Thompson GR (2005). Additive effects of plant sterol and stanol esters to statin therapy, Am J Cardiol 96(1A):37D-39D
5Katan MB et al (2003). Efficacy and safety of plant stanols and sterols in the management of blood cholesterol levels, Mayo Clin Proc 78:965-978
6Rocha M et al (2011). Curr Pharm Des 17(36):4061-75