By Christopher Tack |
Clinical Specialist Physiotherapist
Plant sterols are nature’s anti-cholesterol. They are a fascinating compound found in plants which have an amazing role in the management of the bad cholesterol which can lead to heart disease. They occur naturally in many foods and are often added to foods to make them healthier (such as margarine, orange juice and cereals).
Read on to learn what plant sterols are, how they can assist your cholesterol levels and how best you can get them to become part of your diet.
What Are Plant Sterols?
Plant sterols, or phytosterols, are plant based steroid alcohol compounds. There are approximately 40 different plant sterols identified (1), with greater than 200 forms and related compounds found in plant and marine life (2).
For clarity, the term stanol (rather than sterol) is used to describe saturated sterols which have no double bond in their sterol ring structure.
The most commonly seen plant sterols are sitosterol, campesterol and stigmasterol; all of which are 4-desmethyl sterols (meaning they have no methyl groups attached to their carbon atoms) (1,3).
They also are very structurally similar to the most common animal sterol, cholesterol. The similarity is that all sterols have a chemical ring structure, and differences are between the side chains attached to this ring (1).
They also resemble cholesterol in their primary biological functions, and it is these similarities which give phytosterols some of their health benefits.
Due to their length being virtually identical to that of the phospholipid monolayer which creates a membrane around all cells (2.1nm) (4), these compounds fit easily into these cell membranes. In fact they have an important role in a number of functions for the cell membrane, such as cell stability and temperature management (3,5-6).
Outside the cell membranes, they are found predominantly in the outer layers of the mitochondria (biochemical powerhouse of the cell) and the endoplasmic reticulum (involved in protein and lipid synthesis) (3).
A final function of plant sterols which differentiates them from the animal sterol cholesterol, is their role in being a precursor for a number of plant growth factors (3).
Sources of Plant Sterols
Our daily diets provide about 0.25g of plant sterols, which is doubled if you follow a vegetarian diet (1).
In fact a vegetarian diet can give up to 1g per day of plant sterols (3).
On average the intake of plant sterols is between 0.15-0.4g per day (7, 10, 12-14), and approximately 10% comes from consumption of plant stanols.
✓ Vegetable oils and fats
In the UK, vegetable oils, fats and products derived from oils are considered the richest source of natural plant sterols (3). The daily estimated intake from oils of the most common sterols was 44% sitosterol, 54% stigmasterol and 59% campesterol (3).
✓ Cereals, grains and nuts
The next most abundant source of plant sterols are cereals, grains and nuts (3), with amounts of sitostanol and campestanol in products such as wheat and rye (9). In fact bread and cereals make up approximately 36% of sitosterol intakes (10).
Additionally, to these natural sources sterols can also be esterified (chemically turned into an ester) and added to other food products (for example margarine) (11).
Further sources of plant sterols (including brassicasterol, avenasterol and campesterol) include shellfish (such as clams and oysters) (13,15).
How Do Plant Sterols Effect Cholesterol?
The question remains then, what do plant sterols actually do? The answer to which can be easily summarised.
In essence the amount of plant sterols consumed in diet is negatively correlated with absorption of cholesterol (both total cholesterol and “bad” LDL cholesterol (3).
Remember, the greater the amount of LDL- cholesterol consumed, the greater the risk of cardiovascular and circulatory diseases (16-17).
The use of plant sterols for research into their health benefits has a long history going back 60 years to the 1950s where a crystalline form of these sterols was used to lower cholesterol levels in those with high cholesterol (18-19).
The mechanism by which they do this is through reducing the absorption of cholesterol from the gut. Their similar structure is well suited to compete with cholesterol to a place in the packages formed in the intestines which deliver lipids to cells (20-24). Rather than cholesterol becoming a part of these packages, plant sterols take their place, leaving cholesterol to be removed as waste.
Research further developed in the 1970s where sitostanol and campestanol were shown to be the most effective form of this compound (3).
Approximately 20 years later after stanol esters were formulated and found to reduce lipid levels in people with high cholesterol, the inclusion of such esters into mayonnaise and margarine showed a consistent reduction of cholesterol by 10-15% (25). This reignited the research into plant sterols leading to the production of a variety of different food stuffs which had added sterols to combat heart disease risk.
The clinical and economic benefits of dietary modifications to counter cardiovascular disease, alongside physical activity modification and cholesterol lowering drugs, continues to grow and plant sterols have a large place in public health recommendations and guidelines.
This is particularly emphasised due to the added benefits of anti-oxidants found within the plant based diets which are recommended (26).
Influence of AGE
It should be recognised that the benefits of plant sterols do differ across age groups.
In truth the reduction in LDL cholesterol is significantly greater in older people than younger people (3).
In fact there is a dose response relationship when dosages of plant sterols are increased up to a daily dose of 2g (3).
With awareness that LDL cholesterol levels are greater as we age, at this dose studies show the following statistically significant trend (1):
✓ A 14% reduction of LDL cholesterol for those aged 50-59 years old (20-21, 27, 28)
✓ A 9% reduction of LDL cholesterol for those aged 40-49 years old (29-32)
✓ An 11% reduction of LDL cholesterol for those aged 30-39 years old (29, 31, 33, 34).
It is important to note that whilst the 30-39 year olds actually had a higher percentage reduction of LDL cholesterol, the actual amount of change was less than the 40-49 year old group (because they had more cholesterol to start with).
In the 50-59 year old group a 14% reduction, which would reflect a change of 0.5mmol/ l of LDL cholesterol, would actually reduce risk of heart disease by 25% over 2 years (35).
In younger groups, interestingly this 25% reduction in heart disease risk is similar, because- although the reduction in cholesterol is less- the association is actually stronger in a younger cohort (35).
Plant sterols are potentially atherogenic (just like cholesterol) because of their structure, however because so little of the sterols are absorbed they do not accumulate in the same way as cholesterol (22,36).
Actually no harmful or adverse effects have been observed despite years of review and analysis on both isolated plant sterols or their esters (27, 37-38).
The only concerns which have been noted are that plant sterols can reduce absorption of fat soluble vitamins and reduce beta-carotene concentrations (1). For example, as sterols reduce cholesterol levels we also see an 8% reduction in vitamin E, and a 25% reduction in carotene (28, 29, 33, 39).
However, this issue is minimally important as simply adding more fruit and vegetables to your diet would be effect if countering these deficits (1).
Take Home Message
With cholesterol adding to your potential risk for heart disease it is very much worthwhile examining how you can modify your diet to make yourself healthier.
Including plant based foods into your diet, as well as incorporating vegetables and good fats into cooking, can raise the amount of plant sterols you consume, which will definitively reduce your risk of cardiovascular problems.
If you do not like fruits, salads and vegetables, why not add grains and cereals or even shell fish to get more of these heart protective compounds.
Your heart will thank you for it!