By Joe Leech, Dietitian Authority Nutrition
There are many nutrients that are claimed to be heart healthy.
Among the best known are phytosterols, often added to margarines and dairy products.
Their cholesterol lowering effects are generally well accepted.
However, some serious concerns emerge when looking at the science.
What Are Phytosterols?
Phytosterols, or plant sterols, are a family of molecules related to cholesterol.
They are found in the cell membranes of plants, where they play important roles, just like cholesterol in humans.
The most common phytosterols in the human diet are campesterol, sitosterol and stigmasterol. There are also molecules called plant stanols, which are similar.
This diagram shows the difference between cholesterol and campesterol.
Although we have evolved to function with both types of sterols in the system, the human body definitely prefers cholesterol (1).
Humans actually have two enzymes called sterolins, designed to regulate which sterols can enter the body from the gut. Only tiny amounts of phytosterols get through, whereas around 55% of cholesterol always passes through (2).
Bottom Line: Phytosterols are the plant equivalents of cholesterol in animals. They have a similar molecular structure, but are metabolized differently.
Vegetable Oils and Margarines Are High in Phytosterols
Many healthy plant foods contain considerable amounts of phytosterols.
Throughout the ages, they have been a part of the human diet as a component of nuts, seeds, fruits, vegetables and legumes.
It has been suggested that paleolithic hunter-gatherers, who ate a diet rich in plants, consumed large amounts of phytosterols (3).
In comparison to modern diets, this is not entirely true.
Vegetable oils are actually very high in phytosterols. Because these oils are added to all sorts of processed foods, the total intake of phytosterols is probably greater than ever before (4).
Cereal grains also contain modest amounts of phytosterols, and can be a major source for people who eat a lot of grains (5).
Then phytosterols are added to some processed foods, especially margarines, which are then labelled as “cholesterol lowering” and claimed to help prevent heart disease.
Bottom Line: The amount of phytosterols in the diet is greater than ever before, largely due to high consumption of vegetable oils.
Phytosterols Can Lower Total and LDL Cholesterol, But Does it Matter?
It is a well documented fact that phytosterols can lower cholesterol levels.
2-3 grams of phytosterols per day, for 3-4 weeks, can reduce LDL cholesterol by around 10% (6, 7)
They are particularly effective for people who have high cholesterol, independently of whether they are taking cholesterol-lowering statin drugs or not (6, 8)
They are believed to work by competing for the same enzymes as cholesterol in the gut, effectively preventing cholesterol from being absorbed (1).
However, it’s important to realize that cholesterol levels are just a risk factor for heart disease.
Just because something has positive effects on a risk factor for a disease, it does not guarantee that it prevents the actual disease.
Bottom Line: Phytosterols can reduce LDL cholesterol levels by around 10%, by reducing the absorption of cholesterol from the gut. However, cholesterol levels are just a risk factor, not an actual disease.
Paradoxically, Phytosterols May Increase The Risk of Heart Attacks
Many people assume that phytosterols can prevent heart attacks, because they lower cholesterol.
Unfortunately, there are no studies that actually prove that phytosterols can lower the risk of heart disease, strokes or death.
In fact, many studies show that they can paradoxically increase your risk.
Numerous observational studies in humans have linked high phytosterol intake with an increased risk of cardiovascular disease (9, 10, 11).
Additionally, among heart disease patients in the Scandinavian simvastatin survival study, those with the most phytosterols in the blood were the most likely to get another heart attack (12).
In another study of men with heart disease, the subset of those men with the highest risk of heart attack were at three times greater risk if they had high concentrations of phytosterols in the blood (13).
There are also studies in rats and mice, showing that phytosterols increase plaque buildup in the arteries, cause strokes and shorten lifespan (14, 15).
Even though many health authorities like the American Heart Association still recommend phytosterols to improve heart health, others disagree.
For example, The German Drug Commission, France’s Food Standards Agency (ANSES) and UK’s National Institute for Health and Care Excellence (NICE) all recommend against the use of phytosterols for heart disease prevention (1, 16).
There is also a (very) rare genetic condition called phytosterolemia or sitosterolemia, where people absorb large amounts of phytosterols into the bloodstream.
These people have a massively increased risk of heart disease and liver problems.
Bottom Line: Despite phytosterols leading to reduced cholesterol levels, many studies in both animals and humans suggest that they can increase the risk of heart attacks.
Phytosterols May be Protective Against Cancer
There is also some evidence that phytosterols may lower the risk of cancer.
Human studies have shown that people who consume the most phytosterols have a lower risk of stomach, lung, breast and ovarian cancer (17, 18, 19, 20).
There are also studies in animals, indicating that phytosterols can have anti-cancer properties, helping to slow the growth and spread of tumors (21, 22, 23, 24).
However, the only human studies supporting this are observational in nature. These types of studies can only provide hints, but not proof.
Plant Foods Are Healthy, But Added Phytosterols Are a Disaster
Throughout the ages, phytosterols have been part of the human diet as a component of vegetables, fruits, legumes and other plant foods.
However, the modern diet now contains unnaturally high amounts, largely due to consumption of refined vegetable oils and fortified foods.
High intake of phytosterols is claimed to be heart healthy, but the evidence suggests that they are more likely to cause heart disease, rather than prevent it.
Although eating phytosterols from whole plant foods is fine, it is best to avoid phytosterol-enriched foods and supplements like the plague.