What are plant sterols?

To be absorbed, cholesterol normally mixes with other substances to form what is known as a micelle, which then allows it to pass into the blood stream. Plant sterols, because they are closely related to cholesterol, compete with cholesterol for a place in the micelle.

If a cholesterol molecule can't find a place in the micelle, it is not absorbed and simply passes out of the body with other bowel wastes. If eaten in sufficiently high quantities, sterols have been proven to lower blood cholesterol, particularly the 'bad' LDL-cholesterol.

Where do you find plant sterols?

Plant sterols are found in most plant foods with the largest amounts found in vegetable oils and smaller amounts in nuts, legumes, breads and cereal grains, with still smaller amounts in fruits and vegetables.

Why do you need plant sterols?

If you have high cholesterol, plant sterols added to your diet, can assist in lowering it. In an average diet, we usually only consume between 0.2 and 0.4 g of these sterols a day. This level is too low to have any noticeable effect on our cholesterol.

However, plant sterols, that have been extracted and concentrated during the processing of soy or wood pulp, are added to a number of foods these days, notably margarine spreads and low-fat milks. Adding these foods to your diet is an easy swap and brings significant results. Read my review of the HeartActive low-fat milk here.

Plant sterols are added to other foods such as mayonnaise, dressings, yoghurt and muesli bars. However as it's a small market these 'secondary products' tend come and go.

Sterols were first introduced in Australia and New Zealand in 1999. Other countries also have food enriched with sterols, as well as its hydrogenated version, stanols.

Effectiveness of sterols

There are good clinical trials showing that sterols are effective at reducing blood cholesterol levels. According to the National Heart Foundation, adding 2 to 3 g of sterols a day reduces LDL by 10 to 15 per cent, while having no effect on the good HDL or triglycerides.

This quantity translates to around 1 to 1 ½ tablespoons of spread a day, about the amount you'd spread on three or four slices of bread, or it could come from a combination of spread plus dressing or mayonnaise and some milk.

If you already use a spread, it makes good sense to swap it for one with sterols (for example, Logicol or Pro-activ). While they cost more, the good news is that they're salt-reduced, made from 'good' oils and will complement any medications (like a statin) you may be taking. Similarly if you normally drink a reduced-fat milk, it's worth swapping that for a special sterol one like HeartArtive.

Even if you eat no cholesterol at all (say if you were a vegan), your body still produces its own cholesterol - known as endogenous cholesterol - for use in many bodily functions. Endogenous cholesterol enters the digestive tract via bile and would normally be reabsorbed and then transported to the liver where it could be recycled. Once you start eating sterols, they reduce the absorption of all cholesterol in the digestive tract, which will include that from bile. This means that in addition to a low cholesterol diet, plant sterols have the potential to reduce your cholesterol further, by limiting the absorption of your body's own cholesterol.

Remember, however, that sterols will work best when included with two or three of your daily main meals and they will only work as long as you keeping eating them. Once you stop, your blood cholesterol will return to previous levels.

Safety aspects

Plant sterols have been shown to be safe even when consumed at high levels (say over 5 grams a day) over long periods of time.

They have a history of use in pharmaceuticals that dates back to the 1950s when sterol esters were first prescribed by doctors to control high cholesterol before the advent of today's statin medications. No adverse side effects were ever reported from consuming these even though doses were as high as 30 grams a day – fifteen times what is suggested today for heart health.

There is no significant benefit in consuming more than 2 to 3 grams a day but if you inadvertently took in more than suggested, sterols pose no health risk. This is because plant sterols are poorly absorbed from the digestive tract. The small amounts that are absorbed are known to be rapidly excreted.

The main safety concern has been for fat-soluble vitamins and antioxidants — beta-carotene and related compounds, carotenoids — which were thought to be affected by sterol consumption. However, clinical trials show little effect on fat-soluble vitamins and the observed decreases in carotenoids stayed within the normal range.

Warning

The only group who should not consume sterols are those people with a rare inherited genetic disorder called homozygous sitosterolaemia, a condition where plant sterols are absorbed quite readily from the intestine and can result in heart disease at a young age. This is quite the opposite of most people, for whom sterols are not well absorbed. However, it is extremely rare, occurring in only one in six million people.

Sterols should be viewed as an additional weapon in the war against cholesterol. They are not a substitute for your medication (but they do complement any you take) nor are they a replacement for a healthy diet but they will work in addition to both. It's a situation where the final effect is greater than the sum of the two parts!

Aim for:

2 to 3 serves of sterol-enriched foods each day. One serve means sterol-enriched foods such as:

• 2 teaspoons sterol spread (e.g. Logicol, Pro-activ)
        (this means 10 g which is the amount you'd spread on 1-2 slices of bread)
• 1 glass (250 mL) milk with sterols (e.g. HeartActive)
• 1 carton (200 g) yoghurt with sterols (e.g. Jalna Proheart)
• 1 serve (20 g) mayonnaise or dressing with sterols

         Note: lower intakes are still effective for some people, especially is you're of small weight and height.

This post was sponsored by HeartActive low-fat milk.