Plant sterols: what they are and how they help regulate cholesterol
Plant sterols are compounds similar to cholesterol naturally present in foods of plant origin. Broccoli, Brussels sprouts, cauliflower, green and black olives are particularly rich in them.
Due to their properties and beneficial effects on cholesterol concentrations, these compounds were among the first ingredients to receive authorization from organizations such as the EFSA (European Food Safety Authority) and the FDA (Food and Drug Administration).
Cholesterol, nutrition and lifestyle
Cholesterol is a fat necessary for life: it is in fact one of the main constituents of cell membranes and participates in the synthesis of vitamin D and other substances.
Cholesterol is mainly produced by our body, but some of it can be introduced in the diet.
However, an excess of this fat can be harmful to the well-being of the heart, as it increases the chances of developing illnesses such as heart attack and stroke.
Some lifestyle changes, if maintained over time, can help prevent and control cholesterol levels, among them:
- a healthy diet, rich in fruit and vegetables (natural source of vitamins, minerals and compounds with antioxidant properties), mono and polyunsaturated fatty acids and fiber and low in saturated fatty acids (present in animal-based foods such as whole milk and red meat ), trans fats and simple sugars
- body weight control
- regular physical activity
- quitting bad habits such as smoking.
These changes help reduce high levels of fats, such as cholesterol (LDL cholesterol* – or “bad cholesterol” – and total cholesterol levels) and triglycerides, and instead increase levels of good cholesterol (HDL cholesterol*).
*LDL: Low density lipoprotein; HDL: High density lipoprotein.
Sometimes, however, a lifestyle change alone is not enough to maintain cholesterol levels under control and medical treatment aimed at reducing cholesterol levels is necessary (for instance with statins, products that can slow down the synthesis of bad cholesterol).
What plant sterols are
Plant sterols are natural substances found in fruit and vegetables (broccoli, Brussels sprouts, cauliflower and olives are particularly rich in them), nuts and seeds (walnuts, pistachios, sesame seeds, sunflower seeds), grain, legumes, vegetables oils and other foods of plant origin.
Plant sterols, together with their acid derivatives, stanols (or saturated sterols), belong to the “macro-category” of phytosterols.
Phytosterols are bioactive molecules with proven beneficial properties on cholesterol control, naturally present in foods of plant origin and especially in oils obtained from some plants.
From a structural point of view, the phytosterol molecule is similar to that of cholesterol.
The absorption of these compounds also follows a similar dynamic: phytosterols and cholesterol reach the intestine, where they are incorporated into aggregates of molecules called “micelles” to be transferred into the intestinal cells, where they are assembled with specific proteins to form complexes called “lipoproteins”. Unlike cholesterol, however, phytosterols cannot be produced by the body and are present only if consumed in the diet.
The typical diet of Mediterranean countries provides a daily amount of about 500 mg of phytosterols, which are mainly taken in through the consumption of vegetable oils, grain, chestnuts, vegetables and fresh fruit.
To date, over 250 phytosterols have been identified, of which the most common are sitosterol, campesterol and stigmasterol, whose daily dietary intake corresponds to about 65%, 30% and 3% respectively.
How phytosterols lower cholesterol
Phytosterols are valid natural remedies to contrast cholesterol: they act on the absorption of cholesterol with a competitive mechanism: that is, they interfere with the intestinal absorption of cholesterol, resulting in a reduction of intestinal absorption of this fat by 30-50%.
Daily consumption of 2 g of phytosterols can actually lower cholesterol (total and LDL) by 7-10% (while little or no effect has been shown on HDL cholesterol and triglyceride levels). This effect is already measurable after three weeks of consecutive intake and lasts over time if consumption is regular.
Phytosterols can be incorporated into various products, including yogurt, milk and cheese and soy milk based beverages, fermented milk, margarine spreads, rye bread, sauces and dressings, while the inclusion of phytosterols in other products such as rice-based drinks and fruit juices is still being evaluated.
It has been shown phytosterols assumed in food matrices are just as effective in reducing cholesterol levels as equivalent doses of “free” phytosterols.
Despite the numerous beneficial effects, regular consumption of phytosterols can reduce the levels of beta-carotene (a molecule belonging to the carotenoid family) by up to 17%. The reasons for this effect are not known yet, but this reduction can be compensated by consuming more fresh fruit and vegetables.
Supplements based on plant sterols and phytosterols
The consumption of specifically targeted functional foods and/or food supplements (the so-called “nutraceuticals”) both as an alternative and in addition to treatment with lipid-lowering products, is one of the innovative nutritional strategies for the treatment of changes in the amount of lipids transported in the blood (dyslipidemias).
The administration of supplements (in various forms, including pills or tablets containing complexes of stanols and lecithin and gelatinous capsules containing phytosterolic esters in an oily medium), could represent a flexible tool, to be used in the context of lifestyle modifications aimed at reducing cholesterol levels.
The consumption of phytosterols is generally considered safe and can be recommended to reduce cholesterol levels even in combination with drug therapy.
Integration with phytosterols is aimed exclusively at people wishing to reduce excess cholesterol and is not recommended in the rare cases of patients with phytosterolemia (also called sitosterolemia, which is a rare disease caused by an excessive accumulation of phytosterols in the body).
Additionally, the introduction of phytosterols in industrial food products as cholesterol-lowering ingredients has already been approved by several regulatory agencies around the world, including Health Canada, the Food and Drug Administration (FDA), the European Food Safety Authority (EFSA), the Food Standards Australia New Zealand (FSANZ), and the National Health Surveillance Agency (ANVISA) in Brazil.
People who are undergoing cholesterol-lowering treatment should only take products containing phytosterols under medical supervision.
Products based on phytosterols must be taken in combination with a varied and balanced diet, which includes regular consumption of fruit and vegetables to counteract the effect of phytosterols on the reduction of carotenoid levels.
Consumption of more than 3g/day of plant sterols/stanols should be avoided.
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