Fats

Plant Sterols

We know that reducing high levels of cholesterol in your blood reduces your risk of heart disease. Recent research suggests that consuming plant sterols in the diet can reduce blood cholesterol levels. Plant sterols are found in whole plant foods and so are a regular, though minor part, of our daily diet. Most people eating a normal mixed diet will consume about 200-300 milligrams of plant sterols each day. Individuals who an abundance of plant foods, for example vegetarians, may consume up to 600-700 milligrams each day. Intakes at this level in the diet have a small impact on our blood cholesterol levels, whereas higher intakes can have a more dramatic effect. This can be achieved by enriching foods with plant sterols.

So how do plant sterols lower blood cholesterol levels?

When we eat higher amounts of plant sterols, the absorption of cholesterol in our gut is reduced. Cholesterol in the gut comes from 2 sources. About two-thirds of the cholesterol comes from bile which passes down from the liver as part of the digestion process. The other one-third of the cholesterol entering the gut comes from the animal foods in our daily diets. Plant sterols work in the gut by reducing the absorption of cholesterol into the blood stream. When sufficient plant sterols are consumed they have a two-fold action. They outnumber cholesterol and interfere with its absorption into the bloodstream. In addition, plant sterols will clump with cholesterol to form crystals in the gut so that the cholesterol they contain can no longer be absorbed into the bloodstream, and so continues through the gut and out the other end. The overall effect is a reduction the amount of cholesterol in the body and blood cholesterol levels fall.

Is there research to back up the theory?

There have been several studies (including one in New Zealand at the Department of Human Nutrition, University of Otago) which have shown the cholesterol lowering properties of plant sterols.
One important finding was the form of plant sterol is very important. The early pant sterols used were in a "free" state. But when we look at plant sterols in nature we see that they are normally linked to a fat. When tested in this natural form plant sterols were seen to have an even more potent cholesterol lowering effect. Just 2-3g of plant sterols per day in the form linked to fat were shown to be as effective as up to 30g per day of the "free" form. Plants sterols in the natural form (i.e. bound to a fat) are easily dissolved in vegetable oils. For this reason plant sterols have been added to foods containing vegetable oils, e.g. margarine.
Research where participants have been asked to firstly consume a standard polyunsaturated margarine for 3 weeks, followed by the consumption of a margarine which was enriched with plant sterols have produced interesting results. Compared with the standard margarine, consumption of the margarine enriched with plant sterols reduced total cholesterol levels by 13%. Another study showed a cholesterol lowering effect with the consumption of 2g of plant sterols per day. This is the amount of plant sterols found in 25g of plant sterol-enriched margarine.
On average studies have shown that plant sterols can reduce LDL-cholesterol (the "bad" cholesterol) by about 10%. There is of course some individual variation.
One of the advantages of using plant sterols is that they have no smell or taste and so do not affect the flavour of food.