Plant sterols, or phytosterols, are the equivalent of cholesterol in the vegetable world. These substances, such as campesterol, sitosterol and stigmasterol, closely resemble the animal sterol, cholesterol, and can interact with cholesterol receptors in the gut wall. This blocks the absorption of cholesterol from the diet, and cholesterol secreted into the gut via the bile. As a result, less cholesterol is absorbed and more is voided via the bowels, along with most of the plant sterols which are not significantly absorbed themselves.
Plant sterols food sources
Plant sterols are found in small amounts in most plant foods, such as avocado, wheat germ, oats, nuts, legumes, and vegetable oils such as olive oil and sea buckthorn oil. Foods containing the highest concentration of phytosterols include:
- wheat germ oil
- rice bran oil
- corn oil
- rapeseed or canola oil
- sesame seeds
- sunflower seeds
- pistachio nuts
- pine nuts
- wheat germ
- soy beans.
Although diet should always come first, it is difficult to obtain optimum amounts of sterols from food sources alone. While those following a vegetarian diet obtain the highest amounts, it is almost impossible to obtain the intakes of 2g to 3g plant sterols needed per day to produce meaningful improvements in cholesterol balance.
Dietary intakes of plant sterols
A study in the American Journal of Clinical Nutrition estimated that it is only possible to obtain a moderate phytosterols intake of 459mg per day from a healthy diet, without supplements.
A large trial involving over 22,500 men and women living in Norfolk found that people with the highest dietary intake of plant sterols (average 463mg per day) had a cholesterol level that was 0.25 mmol/l (9.67 mg/dl) lower than those with the lowest plant sterol intake (average 178mg per day) after adjusting for other dietary factors.
If you have a raised cholesterol level, then as well as eating more fruit and vegetables, you would benefit from selecting functional foods fortified with sterols (or the closely related stanols) such as spreads and yoghurts. Plant sterols supplements are one of the easiest ways to boost your intake. The way in which plant sterols block cholesterol absorption is shown in the following clip:
Plant sterol supplements lower cholesterol
Following a plant-based diet that is enriched with phytosterols supplements can lower levels of LDL-cholesterol by around 15%.
The pooled results from 124 studies found that plant sterols supplements lowered LDL-cholesterol by an average of 12% at dose of 3g per day. Phytosterol supplements are even more effective in people with type 2 diabetes; according to one study, plant sterols (at a dose of 1.8g per day for 21 days) reduced LDL-cholesterol levels by 26.8% in people with type 2 diabetes, compared to a reduction of 15.1% in those without diabetes.
Having reviewed all the evidence, the EU has authorised health claims that plant sterol supplements 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.
Supplements tend to provide 800mg plant sterols per tablet, and taking three tablets a day, with or just after meals, can significantly lower your cholesterol levels within 2 to 3 weeks.
Plant sterols and statins
Statin drugs that are prescribed to lower cholesterol levels work in a different way to plant sterols. Statins inhibit an enzyme in the liver, so less cholesterol is made and released into your circulation, while plant sterols block the absorption of cholesterol in the gut.
Because they work in a different way, plant sterols can be combined with statin therapy to lower cholesterol levels even further. This is a great way to boost the effect of statins and avoid having to increase the dose. In fact, adding plant sterols to statin medication is more effective than doubling the statin dose.
Plant sterols side effects
Phytosterols are among the safest supplements with few side effects. The only recognised potential adverse effect of plant sterols is a reduced absorption of some dietary carotenoids. This is easily overcome by eating an additional serving of a carotenoid-rich (yellow or orange) fruit or vegetable per day – something we should all aim to do anyway!
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