During the last decades, chronic disease has become widespread in our population. It is now a significant cause of concern for health authorities worldwide.
According to the World Health Organization (WHO), they are the first cause of death worldwide. 68% of deaths are caused by chronic disease.
Impressively, 40% of them are younger than 70 years old. Cardiovascular disease was the most common cause, followed by cancer, respiratory disease, and diabetes (1).
Similarly, during the last decades, doctors have recommended to increase vegetable consumption to their patients. But why are veggies so beneficial to improve our general health? One of the reasons is plant sterols.
As you will see in this article, plant sterols can have a fundamental role in keeping our health. They keep our cholesterol levels in check, boost immunity, and reduce cardiovascular risk.
Let’s see what are they exactly, how do they work, and how are they beneficial for us.
What are plant sterols?
Plant sterol is the name given to a group of biological compounds similar to cholesterol. If you look at the chemical structure of plant sterols and that of cholesterol, you will see many similarities.
The only difference can be found in the lateral chain. The main sources of plant sterols are vegetable oils. But you can also find them in cereals, bread, stanol margarines, dry fruits, and fresh vegetables (2).
They can be divided into different subgroups, and the biggest of them is called phytosterols. 95% of sterols are phytosterols, especially beta-sitosterol, campesterol, and stigmasterol.
These substances are only found in plants. It is impossible for mammals and other animals to synthesize them. Thus, the only way to obtain them is through the diet.
How do plant sterols work?
Phytosterol substances are often recommended to reduce the cardiovascular risk. This is because they interact with their close relative, cholesterol.
Plant sterols and cholesterol share many similarities, and the former inhibits the absorption of the latter in the intestines.
How do they work?
In their structure, phytosterols have important chemical differences. Due to these chemical differences, they are a bit more soluble in water. Compared to cholesterol, plant sterols are absorbed more rapidly.
They enter a structure in the intestines called miscella faster than cholesteron. This structure is fundamental for fatty acid absorption. And since they take the spot instead of cholesterol, this molecule is eliminated instead of being absorbed (3).
Besides the mechanism above, other mechanisms have been proposed. One of them has to do with the formation of cholesterol esters. This step is fundamental to export cholesterol into the bloodstream.
Otherwise, cholesterol can be absorbed but stays in the gut cell and does not pass to the blood. Some authors have proposed that cholesterol transportation is inhibited. That’s because cholesterol is no longer esterified in the gut cell, and never gets ready to be transported (4).
The mechanisms above work for all types of cholesterol. Dietary cholesterol and cholesterol from the biliary secretions will only be partially absorbed.
These mechanisms in the gut are fantastic. But, what happens once plant sterols are absorbed?
Impressively, the capacity of the gut cell to absorb plant sterols is very small. Only 0.4 to 3.5% of plant sterols are passed into the bloodstream. The least absorbed group is stanols, in a proportion of 0.02 to 0.3%.
So, they are inhibiting cholesterol absorption and taking its place. But they are not being absorbed, either. That is because the body struggles a lot to create esters of these fatty acids in the gut. And only stanol esters are passed into the bloodstream inside of chylomicrons.
Different researchers propose other roles of plant sterols in the organism. Some of them are related to cholesterols. Others are not. Their actual functions are still under research, as well as the factors that predetermine whether or not they are effective in front of cholesterol (5).
Are plant sterols effective at lowering cholesterol?
LDL is a fraction of cholesterol in the blood. When people say bad cholesterol level is high, they are talking about LDL cholesterol. This fraction has a bad reputation because it delivers and scatters fat throughout the system.
This is an important function because fat is essential to create cell membranes. However, a very high serum cholesterol based on LDL means your organism is scattering too much fat. This is deposited in your arteries, and can cause severe problems. That is why cholesterol is considered bad, even if it is necessary for many body processes.
In contrast, we also have good cholesterol, or HDL. This cholesterol particle does the opposite as LDL. Instead of scattering fat, it gathers excess fat from arterial deposits. Thus, it reduces the chance of atherosclerosis.
Many studies show that plant sterols can reduce LDL cholesterol level without affecting HDL levels. This is a very important feature because we want to stop dispersing fat. But we want to reduce atherosclerotic plaques at the same time. That’s why we use the cholesterol lowering effects of plant sterols to reduce atherosclerosis (6).
But how do plant sterols contribute to reducing high cholesterol levels?
One of the principal mechanisms is related to cholesterol absorption, as described above. Plant sterols lower blood cholesterol levels by inhibiting cholesterol absorption. They interfere with intestinal cholesterol absorption and dietary cholesterol does not pass to the bloodstream.
This reduction is significant, and each person experiences a different level. It is estimated that 20 to 80% of cholesterol won’t be absorbed in the presence of high concentration of plant sterols.
What happens next is that the liver starts a compensation mechanism. But even if the liver triggers cholesterol synthesis, the reduction of total cholesterol is significant. It is calculated around 8 to 15%, according to clinical trials (7).
That is why, along with statin treatment, phytosterols are an excellent choice to control familial hypercholesterolemia and other cases of severely high levels of LDL.
The earliest data we have about plant sterols and cholesterol reduction in humans comes from a study in 1953. Back then, the researchers reported that sitosterol reduced cholesterol levels. They proposed it was due to an inhibition of the absorption process (8).
Thereafter, other studies used enriched foods with sterols and plant stanols. This type of enriched foods started to appear in the market around 1999. Then, one of the most important revisions of scientific literature was released in 2003.
In this meta-analysis, the researchers found out that people needed 2 grams of plant sterols to achieve notable reductions of LDL. The typical reduction was around 10%. This number was then reproduced several times by other researchers (9, 10).
In a recent meta-analysis published in 2014, the researchers included 124 studies and their evidence. They showed that the higher the dose of plant sterols you consume, the more pronounced cholesterol reduction you will get. They reported that 2 grams achieved a reduction of 8.4%. But raising the dose to 3.3 grams would achieve a reduction of 12.4% (11).
Surely, the efficacy of plant sterols depends widely on your diet, too. Thus, if you have very high cholesterol levels, it is important to avoid saturated fats. It is also recommended to live a more active live and engage in physical activity. That way, LDL cholesterol will be reduced while HDL cholesterol increases.
What other conditions can plant sterols help?
The most common application of plant sterols is reducing our circulating levels of cholesterol. Thus, it is a useful treatment for hypercholesterolemia. However, it can also treat high triacylglycerol concentrations.
It is useful to prevent coronary heart disease. And some studies have linked plant sterols with immune function.
Let us review each one of these applications and their scientific evidence.
Plant sterols and triacylglycerol reductions
Plant sterols are useful for triacylglycerol (TAG) reduction, too. These are fat particles that are typically high in people with the metabolic syndrome. They apparently lower TAG concentration by one of the following mechanisms (12):
- By increasing the activity of an enzyme that burns fat, called lipoprotein lipase
- By facilitating the uptake of TAG, which then will be burned inside the cell
- By activating a protein called Plasma Lipid Transfer Protein, which collects TAG from the blood, exchanging them for cholesterol particles.
- By reducing the rate of intestinal fat absorption
- By reducing the production of fat transporters by the liver
A study performed in the Maastricht University, at Netherlands evaluated one of these mechanisms. The researchers explored the concentration of lipoproteins in the serum.
These lipoproteins transport fat in the blood, especially TAGs. Finding a reduction would explain why TAG levels are reduced after plant sterol intake.
The individuals enrolled in the study had a dyslipidemic metabolic syndrome. In other words, they had a combination of insulin resistance and high TAG levels. Another group in the study had normal levels of TAGs, and they served as a control group.
The study group with high TAGs experienced a very noticeable reduction of VLDL particles. The individuals with normal TAG concentration had a slight reduction of VLDL particles, too. However, the effect was more pronounced in patients with high concentrations of fat in the blood (13).
This study and many others show that plant sterols reduce TAGs by reducing their blood transporters. The effect is more pronounced in people with high levels of TAGs. Thus, we can use it to control dyslipidemia without affecting normal values in healthy people.
Plant sterols and coronary heart disease
Naturally, plant sterols can reduce the risk of coronary heart disease. They have been recommended for that particular use for decades now. As noted above, plant sterols reduce cholesterol and TAG levels in the blood.
They are both associated to coronary heart disease in different ways. By reducing TAG and cholesterol levels, we are also reducing the cardiovascular risk.
In a scenario of high cholesterol and TAG levels, the excess is deposited in the arteries. Gradually, these deposits become larger, and start causing inflammation. Free radicals start causing oxidation in the area. They act upon LDL particles, creating oxidized LDL.
These oxidized particles activate macrophages, and they eat or engulf the particles in an attempt to destroy them. But what they really do with all of this process is creating a very hard plaque around the arteries. This is known as the atherosclerotic plaque, and it is the first step of coronary heart disease.
By decreasing fat levels in the blood, we are actually reducing the chance of plaque formation. Other recommendations to contribute to this risk reduction include:
- Omega 3 consumption, as in fish oil. It reduces inflammation and improves lipid profile
- Living an active life and combining aerobic and anaerobic exercise to increase HDL synthesis
- Eating a healthier diet and avoiding saturated fats, as discussed above.
All of these lifestyle modifications are useful to prevent cardiovascular disease. And plant sterols can be helpful when consumed in the right proportion (12).
Plant sterols and the immune system
The immune system is rather complex. It includes cells and substances released to target tissues. Inflammation is actually a function of the immune system to fight pathogens and prevent disease.
Allergies are also based on normal functions of the immune system that become exaggerated. Rheumatoid arthritis and multiple sclerosis are based on a confused immune system that no longer distinguish between normal tissue and microbial pathogens.
So, the immune system is designed to fight disease. But an imbalance in cells and substances can cause disease by itself, without any bacteria lurking around. In short, what plant sterols do is modulating different parts of the immune system. They help the immune system find the perfect balance to fight disease without causing problems.
For example, in patients with HIV infection, plant sterols can modulate the activity of T-helper cells. These cells are fundamental to trigger the immune response against a new pathogen. In patients with asthma, a group of cells known as Th2 is overly active and cause allergies.
In this situation, plant sterols can rebalance the equation and modulate the immune response. Similarly, we can see excellent effects in autoimmune diseases, like multiple sclerosis and inflammatory bowel disease. Plant sterols won’t cure the disease, but confer a protective effect. This slows down the progression and may improve the symptoms of these patients.
In patients with high-fat diets, we typically see a fatty liver disease. It is known as non-alcoholic steatohepatitis. In these patients, fat accumulation causes inflammation of the liver.
In time, this inflammation becomes worse and starts causing severe liver problems. Interestingly, plant sterols can counter this inflammation. They do not change the fat content in the liver, but reduce hepatic inflammation (12).
Can plant sterols have side effects?
Plant sterol intake is associated with many benefits for our general health. However, we need to name a few side effects, as well. But first, we need to say that these side effects are only seen in very high doses.
The usual plant sterol intake and average supplementation is unlikely to cause the following symptoms. But if you reach a dose higher than 9 grams a day, you may experience vitamin absorption problems.
Similar to what it does with cholesterol, plant sterols can interfere in vitamin absorption. Fat-soluble vitamins are usually affected, and the most common deficiency is vitamin A.
Serum concentration of vitamin A can reduce by 10 to 20% when you consume plant sterols. Other fat-soluble vitamins can also reduce concentration in the blood. For example, vitamin K, vitamin E, and vitamin D. However, the reduction is not marked and not really important as in vitamin A (14).
Plant sterol supplementations or fortified foods with added plant sterols should be consumed along with a healthy diet. Studies have reported that you’re not likely to experience a significant reduction in vitamin A if your diet already has sufficient carotenoids. So, if you’re consuming added plant sterols, always do it along with 5 portions of fruits and vegetables (15).
Knowing these, many companies that manufacture products with enriched plant sterols have taken action. Some of them include carotenes in their formula to reduce the incidence of this side effect.
Other side effects show up only in people with certain genetic abnormalities. As mentioned above plant sterol absorption is minimal. But these individuals absorb an extremely high proportion of sterols. Thus, they develop a condition known as phytosterolemia.
Their plant sterol levels in the blood are extremely high. In their particular case, sterols start acting against them, creating atherosclerotic plaques, and increasing their cardiovascular risk (16).
Can they have interactions?
Phytosterol esters can be useful to reduce cholesterol levels. So, they do have an interaction with cholesterol-lowering medications. They can further lower cholesterol if you’re receiving statins.
Actually, people who are receiving these medications and still don’t reach adequate levels of cholesterol can also use plant sterols. Then, they would get an LDL reduction of up to 15% additional to that achieved with statins (17). It is important to note, however, that plant sterols are not meant to replace statins. Any nutritional or dosage change in your medications should be supervised by your doctor (18).
We could also say that plant sterols interact with fat-soluble vitamin absorption, as noted above. Other than that, plant sterols are not known to interact with other drugs.
Dosage
The occidental diet does not contain enough plant sterols. It is estimated that we get around 150 to 450 milligrams of dietary phytosterols every day. This is not enough to get all of the benefits listed above in the cardiovascular health and cholesterol levels.
The majority of studies with real benefits on cholesterol, TAG levels, and other diseases use higher doses. The average dose to get health benefits is 2 grams a day. 3 grams a day is still considered a safe dose. However, the European Food Safety Authority recommends that we never exceed 3 grams. Doing so would likely trigger vitamin A deficiency, as noted above (19).
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Conclusion
For decades, doctors have recommended to increase the intake of fruits and vegetables. It is one of the measures aimed to reducing our cardiovascular risk. That is because fruits and vegetables have plant sterols.
These substances reduce our cardiovascular risk by reducing cholesterol absorption. With lower LDL cholesterol levels, there is a lower chance to suffer from atherosclerosis.
Similarly, plant sterols have applications in the field of immunology. They balance the equation and have a protective effect against immune-mediated diseases. To obtain these benefits, we should increase the plant sterol dose. Our western diet usually has no more than 450 mg of plant sterols a day. But we need at least 2 grams a day to get these benefits.
Consuming 2 grams a day is possible through enriched foods and supplementation. However, it is still important to eat at least 5 portions of fruits and vegetables every day. This will reduce the change of getting a vitamin A deficiency, which is a possible side effect of a higher plant sterol dose.
