Phytosterols: What Are They, and Do They Have Downsides?

Phytosterols, also known as plant sterols, are a family of molecules related to cholesterol.

They’re found naturally in a variety of plants. Like cholesterol, they’re a key structural component of cell membranes (1).

Campesterol, beta-sitosterol, and stigmasterol are the most common plant-derived phytosterols you get from your diet. They’re found naturally in foods like nuts, seeds, and vegetable oils, and they’re added to some processed foods like margarine (1).

Because phytosterols can block the absorption of cholesterol, they’re often promoted as a way to improve heart health and decrease blood levels of LDL (bad) cholesterol (2).

However, it’s estimated that only around 2% of phytosterols found in food are absorbed by your body, compared with around 50% of cholesterol (2).

SUMMARY

Phytosterols are a type of compound found in nuts, seeds, vegetable oil, and margarine. They’re often used to decrease cholesterol levels, though your body only absorbs small amounts of them.

Many healthy plant foods contain considerable amounts of phytosterols, including (3, 4):

• Nuts: pistachios, macadamia nuts, almonds, cashews, peanuts, hazelnuts
• Seeds: pumpkin seeds, sunflower seeds, watermelon seeds
• Fruits: pineapples, oranges, berries, bananas, apples, apricots
• Vegetables: artichokes, broccoli, green beans, cabbage, asparagus, sweet potatoes, celery, cauliflower
• Legumes: chickpeas, lentils, mung beans, adzuki beans, soybeans
• Oils: olive oil, argan oil, sunflower oil, canola oil

For this reason, some research has found that people eating a vegan or vegetarian diet typically consume more phytosterols than people who follow nonvegetarian diets (5).

Similarly, it’s estimated that the diet of ancient Paleolithic hunter-gatherers, which was rich in plant foods like nuts and seeds, contained around 2.5–5 times as many phytosterols as the average modern diet (6).

While these ancient groups of people got plenty of phytosterols from plant foods, many people today regularly get added phytosterols from refined vegetable oils and processed foods like margarine.

Furthermore, cereal grains contain some phytosterols and can be a good source for people who eat a lot of grains (3, 4, 7).

It’s generally believed that consuming at least 2 grams of phytosterols per day could significantly reduce LDL (bad) cholesterol levels (8).

For reference, 1 cup (170 grams) of chickpeas contains approximately 206 mg of phytosterols, a 3.5-ounce (100-gram) serving of sweet potato contains 105 mg, and 1 tablespoon (14 grams) of sunflower oil contains 69 mg (3, 4).

Keep in mind that refined vegetable oils, margarine, or phytosterol supplements don’t provide other beneficial nutrients like fiber or vitamins C, K, or A. Thus, it’s best to simply eat more whole foods that contain phytosterols if you’d like to boost your intake.

SUMMARY

Plant foods like nuts, seeds, vegetables, and legumes are rich in phytosterols. Many people also regularly consume refined vegetable oils and processed foods that often contain added phytosterols.

Studies show that phytosterols may offer several benefits, especially when it comes to cholesterol levels and cancer risk.

Might reduce cholesterol levels

In your gut, phytosterols compete with dietary cholesterol for certain enzymes needed for their metabolism. This can reduce cholesterol absorption by a whopping 30–50% (8).

According to one review, consuming at least 2 grams of phytosterols per day could reduce your blood levels of LDL (bad) cholesterol by around 8–10%. However, it’s worth noting that this study used high-dose supplements, not natural food sources (8).

Phytosterols are particularly useful for people who have high cholesterol levels, as they’ve been shown to boost the effectiveness of statins, a type of cholesterol-lowering medication (9).

Although cholesterol doesn’t directly cause heart problems, having high levels of cholesterol in your blood is a risk factor for heart disease (10).

May lower the risk of certain cancers

Some evidence suggests that phytosterols may lower your risk of some cancers.

Human studies show that consuming a high amount of phytosterols could be linked to a lower risk of stomach, lung, liver, breast, prostate, and ovarian cancer (11, 12).

Test-tube and animal studies similarly indicate that phytosterols may have cancer-fighting properties and could slow the growth and spread of tumors (13, 14, 15).

Keep in mind, though, that the studies conducted in humans don’t account for other factors that could play a role in cancer development, such as family history, physical activity, alcohol consumption, and tobacco use.

What’s more, many of the test-tube and animal studies were conducted using large amounts of highly concentrated phytosterols that exceed the amount you’d naturally get from your diet.

Therefore, more research is needed to determine how phytosterols may affect cancer growth in humans when consumed in normal amounts as part of a healthy diet.

summary

Phytosterols can decrease cholesterol levels by 8–10%. Some studies also suggest that they could be linked to a lower risk of cancer, although more research is needed.

Although phytosterols may be associated with several benefits, there are a also few downsides to consider.

May increase plaque buildup

Some research shows that phytosterols could increase the buildup of plaque in your arteries, which can contribute to a condition known as atherosclerosis (16, 17).

This can narrow the arteries, making it harder for your heart to pump blood throughout your body (18).

This is especially worth noting for people with a genetic condition called sitosterolemia. Sitosterolemia causes the body to absorb large amounts of phytosterols into the bloodstream, increasing the risk of plaque buildup and heart disease (19).

Still, research is conflicting.

For example, older and newer studies in humans and animals have found that increased consumption of phytosterols isn’t associated with a higher risk of atherosclerosis. Rather, they’ve found that it may promote blood flow by dilating the blood vessels (20, 21, 22).

As such, more research is needed on the topic.

Could increase heart disease risk

Although research shows that phytosterols might decrease levels of LDL (bad) cholesterol, studies on whether they can reduce the risk of heart disease have found mixed results.

For example, one 2007 study didn’t find an increased risk of heart disease among people with higher blood levels of phytosterols (23).

Additionally, a 12-week study in 232 people with high cholesterol showed that consuming a low fat spread with 3 grams of added phytosterols per day did not affect markers of circulatory health (24).

On the other hand, several older studies have found that increased levels of phytosterols in the blood may be linked to a higher risk of developing heart disease or having a heart attack (25, 26, 27).

One review also noted that some people have genetic variations in certain proteins that increase the absorption of phytosterols in the gut — and that having these proteins could be linked to increased heart disease risk (16).

SUMMARY

Some studies suggest that phytosterols could increase plaque buildup in your blood vessels and may be tied to a higher risk of heart disease. However, more research is needed.

For centuries, phytosterols have been part of the human diet as a component of vegetables, fruits, legumes, and other plant foods.

Today, they’re added to some processed foods, including many types of margarine.

Studies show that a high intake of phytosterols might be associated with reduced cholesterol levels and a lower risk of certain types of cancer.

Yet, research on their other potential effects on heart health — including how they affect plaque buildup and heart disease — has turned up mixed results. Thus, more research is needed.

Ultimately, it’s best to increase your intake by enjoying more nutrient-dense plant foods rather than phytosterol-enriched processed foods and supplements.