Plant sterols, or phytosterols, are fats which are components of plant cell membranes. More than 40 sterols have been identified, of which beta-sitosterol, campesterol and stigmasterol are the most abundant. They are similar in structure to cholesterol; however, unlike cholesterol, plant sterols are only absorbed in trace amounts by the human body. Their ability to lower total cholesterol as well as LDL cholesterol (known as the “bad” cholesterol) has been studied extensively for over 50 years with over 40 clinical trials attesting to their efficacy. In contrast, they do not lower serum levels of HDL-cholesterol, known to be beneficial for preventing cardiovascular disease.
The Masai diet
The diets of our ancestors were rich in plant sterols, providing a daily intake of approximately 1000mg, in contrast to present-day plant sterol consumption, which varies between 200mg and 450mg per day.
This difference is due to current dietary habits that are heavily influenced by convenience foods and quick-fix snacks that are usually nutrient deficient and low in plant-based ingredients. The amount of plant sterols needed to be consumed for significant cholesterol-lowering effects is 1.5-2g per day, although some studies show that plant sterols in foods are active at doses as low as 150mg.
Interestingly, the traditional diet of the East African Masai tribe is dominated by a high intake of saturated animal fats, yet despite this their serum cholesterol levels remains low and cardiovascular disease is almost non-existent. This is thought to be due to their practice of adding various plants to milk and meat-based soups, drinking herbal teas with their meals, regularly using medicinal plants and frequently chewing on tree barks and gums. Medical doctors and anthropologists who studied the tribe found that many of the common Masai plant-derived food additives contain cholesterol-lowering plant sterols.
Lowering cholesterol
The main mechanism responsible for the cholesterol-lowering effect of plant sterols is the inhibition of intestinal cholesterol absorption. Plant sterols lower total serum cholesterol levels by displacing cholesterol from micelles, extremely small particles formed in the gut.
These micelles are needed to transport cholesterol through the intestinal wall. When cholesterol is displaced from the micelle, its absorption into the blood is prevented. Another means by which plant sterols inhibit cholesterol absorption involves their co-crystallisation with cholesterol to form insoluble mixed crystals that are also unable to pass across the intestinal wall.
About 1000mg of cholesterol is secreted into the bile each day, 60 per cent of which is reabsorbed and the rest excreted. It is thought that plant sterols may also work by increasing the amount of cholesterol that is recirculated into the bile, thereby enhancing its elimination from the body.
Sterols in food
Plant sterols are present in high amounts in cold-pressed, unrefined vegetable oils such as rice bran, flaxseed, olive, sesame and wheat germ oils, nuts and seeds. There are also some sterols in algae such as seaweed and in spirulina, fruit, vegetables, cereals and legumes.
Eat your nuts!
Nuts are one of the richest sources of plant sterols in the typical Western diet. Studies have shown that people consuming diets that contain between 40 and 100g of nuts such as almonds, hazelnuts, macadamias, pecans, pistachios and walnuts have lower serum triglyceride, total cholesterol and LDL cholesterol levels. Pistachios, in particular, are an excellent source of plant sterols with 100g of pistachios providing 214mg of plant sterols.
Food fortification
Since studies have shown that the amount of plant sterols needed to be consumed to lower cholesterol levels by 10 per cent is between one and three grams per day — an amount significantly higher than that consumed in the typical Western diet — the fortification of various foods such as margarines and table spreads has become common practice.
While eating fortified foods can help increase the amount of plant sterols in your diet, you would still need to consume several servings of these foods each day for therapeutic effects. For example, in order to lower your cholesterol levels by 10 per cent you would need to eat approximately 25g or five teaspoons of fortified table spread or margarine every day.
In the past, many table margarines have been high in trans-fatty acids which are linked to an increased risk of cardiovascular diseases. Trans-fatty acids are created when manufacturers use a process called partial hydrogenation. This process turns liquid oil into a semi-solid form, such as shortening or margarine. Most table margarines have sought to eliminate trans fats these days but check the labels for trans-fat content and look out for ingredients containing partially hydrogenated oils.
Plant sterols in your diet
Ensure you get adequate amounts of plant sterols in your diet by eating a variety of plant-based foods rich in these compounds with each meal every day. Try a handful of pistachios for your morning and afternoon snacks, use cold-pressed vegetable oils such as flaxseed oil for salad dressings, put unhulled tahini (sesame seed spread) on your toast or add a couple of teaspoons of spirulina powder to your breakfast smoothie.
When consuming a diet high in plant sterols, be aware that the absorption of carotenoids and possibly other fat-soluble vitamins such as vitamin E may be reduced. One additional serving of fruit and vegetables high in carotenoids such as carrots, pumpkin, broccoli, apricots or mangoes will offset any drop in your carotenoid concentrations.
Phytosterols in nature
| Food Sources: | Plant sterol content: |
| Rice bran oil | 1190mg/100g |
| Sunflower seeds | 534mg/100g |
| Wheat germ | 413mg/100g |
| Sesame seeds | 400mg/100g |
| Flaxseed oil | 338mg/100g |
| Pistachios | 214mg/100g |
| Almonds | 141mg/100g |
Source: United States Department of Agriculture Nutrient Database
Saskia Brown is a qualified naturopath with degrees in naturopathy and the social sciences. She is currently practising in Neutral Bay specialising in weight loss, allergies and asthma. E: saskia@saskiabrown.com; W: www.saskiabrown.com.
