Many nutrients are claimed to be good for your heart.

Among the best known are phytosterols, often added to margarines and dairy products.

Their cholesterol-lowering effects are generally well accepted.

However, scientific research reveals some serious concerns.

This article explains what phytosterols are and how they might harm your health.

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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 your diet are campesterol, sitosterol, and stigmasterol. Plant stanols — another compound occurring in your diet — are similar.

Although people have evolved to function with both cholesterol and phytosterol in their systems, your body prefers cholesterol ().

In fact, you have two enzymes called sterolins that regulate which sterols can enter your body from the gut.

Only tiny amounts of phytosterols pass through — compared to around 55% of cholesterol ().

SUMMARY Phytosterols are the plant equivalents of cholesterol in animals. They have a similar molecular structure but are metabolized differently.

Many healthy plant foods — including nuts, seeds, fruits, vegetables, and legumes — contain considerable amounts of phytosterols.

It has been suggested that paleolithic hunter-gatherers, who ate a diet rich in plants, consumed large amounts of phytosterols ().

However, in comparison to modern diets, this is not entirely true.

Vegetable oils are very high in phytosterols. Because these oils are added to many processed foods, the total dietary intake of phytosterols is probably greater than ever before ().

Cereal grains also contain modest amounts of phytosterols and can be a major source for people who eat a lot of grains ().

What’s more, phytosterols are added to margarines, which are then labeled "cholesterol lowering" and claimed to help prevent heart disease.

However, this assertion is dubious.

SUMMARY Vegetable oils and margarines contain high amounts of phytosterols. Because vegetable oils are added to many processed foods, the concentration of phytosterols in the diet is likely greater than ever before.

It is a well-documented fact that phytosterols can lower cholesterol levels.

Eating 2–3 grams of phytosterols per day for 3–4 weeks can reduce “bad” LDL cholesterol by around 10% (, ).

This is particularly effective for people who have high cholesterol — whether or not they’re taking cholesterol-lowering statin drugs (, ).

Phytosterol is believed to work by competing for the same enzymes as cholesterol in your gut, effectively preventing cholesterol from being absorbed ().

Although high cholesterol levels are associated with an increased risk of heart disease, they are likely not the cause of heart disease.

For this reason, it is unclear whether reducing your cholesterol levels has any effect on heart disease risk.

SUMMARY Phytosterols can reduce “bad” LDL cholesterol levels by around 10%. However, this may not improve your heart health.

Many people assume that phytosterols can prevent heart attacks because they lower cholesterol.

Yet, no studies indicate that phytosterols can lower your risk of heart disease, strokes, or death.

Paradoxically, phytosterols may increase your risk. Numerous human studies link high phytosterol intake with an increased risk of heart disease (, , ).

Additionally, among people with heart disease in a large Scandinavian study, those with the most phytosterols were most likely to get another heart attack ().

In another study in men with heart disease, those with the highest risk of heart attack were at three times greater risk if they had high concentrations of phytosterols in the blood ().

What’s more, studies in rats and mice show that phytosterols increase plaque buildup in the arteries, cause strokes, and shorten lifespan (, ).

Even though many health authorities like the American Heart Association still recommend phytosterols to improve heart health, others disagree.

For example, Germany’s Drug Commission, France's Food Standards Agency (ANSES) and the UK's National Institute for Health and Care Excellence (NICE) all discourage the use of phytosterols for heart disease prevention (, 16).

Keep in mind that a rare genetic condition called phytosterolemia or sitosterolemia makes some people absorb large amounts of phytosterols into their bloodstream. This increases heart disease risk ().

SUMMARY While phytosterols lead to reduced cholesterol levels, many studies suggest that they can increase your risk of heart disease.

Some evidence suggests that phytosterols may lower your risk of cancer.

Human studies show that people who consume the most phytosterols have a lower risk of stomach, lung, breast, and ovarian cancer (, , , ).

Studies in animals also indicate that phytosterols may have anticancer properties, helping to slow the growth and spread of tumors (, , , ).

However, the only human studies supporting this are observational in nature. This type of research does not provide scientific proof.

Thus, more research is needed.

SUMMARY Human and animal studies suggest that phytosterol intake is associated with a reduced risk of cancer. However, more research is needed.

For millennia, 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.

While high intake of phytosterols is claimed to be heart-healthy, evidence suggests that they are more likely to cause heart disease than prevent it.

Although it’s fine to eat phytosterols from whole plant foods, it’s best to avoid phytosterol-enriched foods and supplements.