Phytosterols

Phytosterols, which encompass plant sterols and stanols, are phytosteroids similar to cholesterol which occur in plants and vary only in carbon side chains and/or presence or absence of a double bond. Stanols are saturated sterols, having no double bonds in the sterol ring structure. More than 200 sterols and related compounds have been identified. Free phytosterols extracted from oils are insoluble in water, relatively insoluble in oil, and soluble in alcohols.

Phytosterol-enriched foods and dietary supplements have been marketed for decades. Despite well documented LDL cholesterol lowering effects, no scientifically proven evidence of any beneficial effect on cardiovascular disease (CVD) or overall mortality exists.

The molecule on the left is β-sitosterol. Nomenclature for steroid skeleton is on the right.

The richest naturally occurring sources of phytosterols are vegetable oils and products made from them. They can be present in the free form and as esters of fatty acid/cinnamic acid or as glycosides, respectively. The bound form is usually hydrolyzed in the small intestines by pancreatic enzymes. Nuts, which are rich in phytosterols, are often eaten in smaller amounts, but can still significantly contribute to total phytosterol intake. Cereal products, vegetables, fruit and berries, which are not as rich in phytosterols, may also be significant sources of phytosterols due to their higher intakes. The intake of naturally occurring phytosterols ranges between ~150–450 mg/day depending on eating habits. Specially designed vegetarian experimental diets have been produced yielding upwards of 700 mg/day. The most commonly occurring phytosterols in the human diet are β-sitosterol, campesterol and stigmasterol, which account for about 65%, 30% and 3% of diet contents, respectively. The most common plant stanols in the human diet are sitostanol and campestanol, which combined make up about 5% of dietary phytosterol.

The European Foods Safety Authority (EFSA) concluded that blood cholesterol can be reduced on average by 7 to 10.5% if a person consumes 1.5 to 2.4 grams of plant sterols and stanols per day, an effect usually established within 2–3 weeks. Longer-term studies extending up to 85 weeks showed that the cholesterol-lowering effect could be sustained. Based on this and other efficacy data, the EFSA scientific panel provided the following health advisory: “Plant sterols have been shown to lower/reduce blood cholesterol. Blood cholesterol lowering may reduce the risk of coronary heart disease".

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