Plant sterols: Do they work?

Foods enriched with plant sterols are showing up in Canadian grocery stores. But can they really protect your heart?

Plant sterols: Do they work?

Source: Web exclusive, January 2011

The aisles at your local supermarket are now more crowded than ever with products that claim to improve your health. The latest ones? A new yogurt and margarine that contain compounds called plant sterols (or phytosterols), and claim they’ll lower your bad cholesterol levels. This could be quite an attractive offer for many people’more than 40 percent of Canadians have high cholesterol, a major risk factor for heart disease. But can foods fortified with plant sterols really help? Read on to get to the heart of the matter.

What’s new about plant sterols

In May 2010, Health Canada agreed to allow foods fortified with plant sterols into Canadian supermarkets, along with the health claim that "plant sterols can help lower cholesterol." Astro BioBest probiotic yogourt with Plant Sterols and Becel pro.activ calorie-reduced margarine with plant sterols are the first plant-sterol-enriched products to hit the shelves. But Health Canada has also approved the addition of the compounds to other spreads, mayonnaise, salad dressing, and vegetable and fruit juices. Many such sterol-enriched products are already available in the United States and Europe, where regulators have allowed the compounds to be added to foods for more than five years.

How plant sterols work

Plant sterols are a group of naturally occurring molecules that closely resemble cholesterol, an essential fat used by your body to manufacture hormones and cell membranes. There are at least 250 different plant sterols in the foods we eat, every day especially vegetable oils, seeds, nuts, cereals and legumes, veggies and fruits. The compounds have become a darling of the food industry because they have therapeutic effects in humans: specifically, they lower levels of LDL (or "bad") cholesterol in the bloodstream by interfering with cholesterol absorption in the small intestine. (They have little effect on HDL or "good" cholesterol levels.) LDL cholesterol can lead to the buildup of plaque in arteries (atherosclerosis), a major factor in heart disease and stroke.

The science behind sterols

The health benefits of plant sterols have been recognized since the 1950s, making them “one of the first items to play a significant role in the development of functional foods,” says Mohammed Moghadasian, associate professor in the department of Human Nutritional Sciences at the University of Manitoba and an expert on plant sterols. Since the mid-1990s, there have been dozens of randomized control trials looking at the effect of foods enriched with plant sterols on blood lipids, including LDL cholesterol. In one pivotal study published in the New England Journal of Medicine, participants with high cholesterol ate margarine fortified with plant sterols (1.8 to 2.6 grams) everyday. After one year, their LDL cholesterol levels had decreased by about 14 percent. LDL levels in the control group, which did not consume margarine with sterols, had decreased by only one percent. Moghadasian says that on average, plant sterols lower LDL cholesterol levels by about 10 percent.

Is this enough to fend off heart disease? In his own studies conducted on mice, Moghadasian has shown that plant sterols reduce atherosclerosis by as much as 50 percent, but this has yet to be proven in humans. Still, researchers estimate that a 10-percent reduction in LDL cholesterol levels is enough to reduce the long-term risk of cardiovascular disease by as much as 20 percent.

Are they safe?

Evidence from the United States and Europe, where plant sterols have been added to foods for up to 10 years, shows that sterols are safe. Health Canada has set the upper limit for consumption at three grams per day for adults or one gram per day for children. However, the agency doesn’t recommend that children or pregnant or breastfeeding women consume products enriched with plant sterols’not because of safety concerns but because the effects of cholesterol-lowering foods haven’t been well studied in these groups.

There is one group for whom plant sterols are considered unsafe’people who suffer from sitosterolemia, a very rare genetic disease, must avoid foods rich in plant sterols. People with sitosterolemia absorb plant sterols into their blood, leading to high cholesterol and the development of heart disease at a relatively young age.

The best sources of plant sterols

Plant sterols in whole foods that are consumed as part of a  regular diet have positive effects on cholesterol levels: A 2004 study of the effects of dietary plant sterols on LDL cholesterol showed that the more sterols consumed as food, the lower the levels of LDL cholesterol in the bloodstream. But studies also show that we consume only about 300 mg of the compounds per day’far fewer than the two grams per day that experts say is needed to lower the risk of heart disease. (Beyond two grams per day, studies have shown little additional benefit.) Health Canada allows foods enriched with plant sterols to contain up to one gram per serving, so two servings or more may be required to get the recommended daily amount.

Who should add plant sterols to their diet?

Studies have shown that plant sterols offer the greatest benefit to people with mildly high cholesterol, Moghadasian states. There’s also good evidence that combining plant sterols with cholesterol-lowering medications, such as statins, and other lifestyle changes has an additive effect, reducing LDL cholesterol more than any one of these therapies alone. A study authored by David Jenkins, Canada Research Chair in Nutrition and Metabolism, looked at the effects of pairing plant sterols with other cholesterol-lowering foods. The result? Consuming foods rich in plant sterols, soluble fiber, soy protein and nuts can lower LDL cholesterol by 28 to 35 percent, a range that is similar to cholesterol-lowering drugs. So if your doctor has told you that you have high cholesterol, you may want to talk to him or her about adding foods fortified with plant sterols to your diet.  However, if you don’t have high cholesterol, there’s no need to buy a product fortified with plant sterols, Moghadasian says. Instead, keep cholesterol levels in check by increasing your exercise, monitoring your weight and making simple changes to your diet, such as cutting down on saturated fats.

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