By Stephen Hussey, MS, DC

All living things have sterols that fulfill vital functions in their bodies, especially providing structure and integrity to cell membranes. Since animals have cholesterol and plants have phytosterol, does that mean, de facto, that cholesterol is better for humans than phytosterol? The answer is yes.

Both forms of these sterols are commonly consumed because most humans eat an omnivorous diet. Cholesterol in our diets comes from the animal foods we eat. The overwhelming majority of phytosterol in the modern diet come from vegetable oils (seed oils), such as corn oil, soy oil, canola oil, sunflower oil, and safflower oil. We also get phytosterols in smaller amounts from foods such as olive oil, coconut oil, and avocados. When we eat these two sterols together, they in fact compete for absorption in the intestines. 

Humans are well designed to absorb fat because of our developed gallbladder; this is a characteristic we share with carnivores. Since the human body is a mostly watery environment, and fat does not dissolve in water, we need the bile salts secreted from the gallbladder to absorb the fats we eat.

Fat and Vitamin D Absorption

Sometimes when people supplement vitamin D, they don’t see the rise in blood levels that they expect. I see this frequently in blood work of people taking high doses of vitamin D. This is probably because they’re not taking the vitamin D with a high-fat meal; while D supplements come packaged in fat, it is not enough fat to stimulate enough bile. Without enough bile, not much fat is absorbed, and since vitamin D is fat soluble (transported in fats), the vitamin D is not absorbed either.

By eating both phytosterols and cholesterols, the body attempts to absorb both types of fat, often resulting in less absorption of cholesterol and decreased blood levels of cholesterol. This is why, since it is thought that lowering cholesterol will prevent heart disease, many doctors recommend foods with lots of plant sterols such as margarine and vegetable oils. Interestingly, in the case of phytosterols, the gut has a mechanism—an ATP-binding cassette transporter protein in the gut lumen—that places as much of the phytosterols it absorbs back into the intestines to eliminate it with other waste. In other words: The body doesn’t want too much of it.

Phytosterol Metabolism

Sitosterolemia is a genetic condition in which this mechanism to return absorbed phytosterols into the intestines is not present. The condition is characterized by phytosterol deposits in the skin (xanthomas) or eyes (xanthelesma and arcus senilis). People with this condition also have increased risk of stroke and heart disease because the phytosterols build up in arteries, as well as in red blood cells, which causes the red blood cells to clump up. People with this condition can have platelet dysfunction causing abnormal bleeding, and they are at higher risk for diabetes because the phytosterols interfere with cholesterol, impairing insulin receptor function.

Some of these symptoms are from the body’s inability to get rid of the phytosterols efficiently, but the more problematic symptoms are due to the effects of phytosterols on red blood cells. A red blood cell is shaped like a disc with a slight depression in the middle, similar to a doughnut. The cell can maintain this shape because it has cholesterol in its membrane. When there are too many phytosterols and not enough cholesterol in the body, the red blood cells use phytosterols for the cell membranes instead. When this happens, the red blood cells lose pliability, become more rigid, and often clump together or get more easily stuck in tight spaces. This increases the risk of stroke and heart disease, interferes with delivery of nutrients, and causes microcirculation issues.

Research Comparing Sterols

There’s an interesting body of research to back this up. For example, in one study published in the Journal of the American College of Cardiology, researchers fed two groups of rodents an animal-fat-based diet but supplemented one of the groups with phytosterols. In the unsupplemented group, the rats’ arteries stayed dilated, and in the supplemented group their arteries became restricted. In a second part of the same study, the researchers looked at people who needed replacement heart valves and found a correlation between diets high in plant sterol and plant sterols deposited on the heart valves.

Researchers surveyed 48,188 people about their diet, placing them in one of three groups—those who ate any kind of meat, those who ate no meat except fish, and vegetarians—and then looked at health outcomes among the groups. They found that meat eaters had a slightly higher risk of ischemic heart disease—but remember, this is epidemiology; they only looked at meat eating, not whether the participants also ate processed grains, sugars, and vegetable oils. They found that the vegetarians had 20 percent higher risk of hemorrhagic and total stroke. In order for the researchers to put participants into the vegetarian group, they had to have claimed to eat no meat, fish, or eggs, so it is reasonable to assume that they would have had much less animal fats in their diet and therefore much higher amounts of plant fats, which possibly led to an increase in stroke. It seems likely that the phytosterols are problematic, especially in high amounts. All this said, it’s important to acknowledge that people with a genetic predisposition to high levels of plant sterols in their blood develop atherosclerosis prematurely, so this genetic predisposition is a factor in outcome.

In 2015, researchers reviewed all the associational literature on high levels of plant sterols in the blood and development of cardiovascular disease. Four studies showed no association, four showed an association between higher presence of plant sterols and less cardiovascular disease, and nineteen studies showed presence of higher plant sterols in the blood linked with higher risk of cardiovascular disease. These are associational studies, but the association is heavy in one direction. The authors of the review are hesitant in their conclusion yet clear about what their work signals: “These discordant findings make it impossible to draw any firm conclusions, even though the largest prospective trials have suggested that high plasma levels of plant sterols increase CV risk. The available data are still not sufficient to confirm whether plant sterol consumption increases CV risk, although they do suggest the presence of such a risk and so cannot be ignored.”

Role of Sterols in Health and Disease

Before we discuss the main sources of these phytosterols in food, it’s important to note that diet is not the only source. As we know, the body tries to rid itself of excess plant fats by depositing absorbed sterols back in the intestines. However, if the intestines are overloaded, we end up with more absorption. What can overload the system besides food? Cholesterol-lowering drugs. Interfering with the production of cholesterol with a statin drug prevents the reabsorption of cholesterol in the liver and therefore more plant sterols are absorbed instead. 

Some sources of plant sterols contribute to insulin resistance. Plant fats are much higher in unsaturated fats, and when we burn these fats rather than saturated fats for fuel, they change the way our cellular metabolism works. This changes the resulting ratio of FADH2 and NADH, which determines if our fat cells are sensitive to insulin or resistant to it. The tricky thing is that we don’t want an insulin-resistant body, but we do want insulin-resistant fat cells. The reason for this is that insulin is the number one fat-storing hormone, and if our fat cells are insulin resistant, we will not store excess fat. Eating unsaturated fat creates a ratio of FADH2 to NADH that makes fat cells insulin sensitive and eating saturated fat creates a ratio that makes our fat cells insulin resistant. This phenomenon has led to the misconception that saturated fat leads to insulin resistance.

If we eat lots of unsaturated plant fats, we create insulin-sensitive fat cells that take up glucose and fats and store them, creating weight gain. This happens because the mitochondria of those fat cells become dysfunctional when burning plant fats. As those fat cells expand, they send out insulin-resistant signals called lipokines to the rest of the body. This leads to the metabolic derangement that underlies the chronic diseases that plague our society, including cardiovascular disease.

Sources of Sterols

So, where are these plant sterols found? In fats derived from plants. That includes avocados and avocado oil, olives and olive oil, coconut oil, nuts, seeds, and all the vegetable/seed oils (soybean, corn, canola, sunflower, and so forth). The seed oils have higher levels of plant sterols than any of the other plant oils and so it is no wonder that we have seen a steady increase in heart disease since seed oils entered mass production and became widely available in the early 1900s. 

While olive oil, avocado oil, and coconut oil do have plant sterols, they contain much smaller amounts than the seed oils do, and I believe they are a safer option if you are going to eat plant fats. Be cautious though, many olive and avocado oil companies are not honest about what is in the oils. One study found that 82 percent of the avocado oil brands they tested had soybean oil in them, and some of the brands tested to be near 100 percent soybean oil. We also should be careful about how we source our animal foods. If the animals we eat are fed a diet high in soy and corn, then in some animals (namely chickens and pigs), the fat in their bodies contains plant sterols that may be passed on to us. Because of differences in their digestive systems, this is not the case for ruminant animals like cows. 

All this is to say that humans are designed to eat and use animal fats, but we can survive on plant fats when animal-based fats are not available. Long-term high use of plant sterols can lead to many health problems. When possible, we should stick to fats that come naturally from animals. This makes intuitive sense: we don’t have to over process lard, beef tallow, butter, bone marrow, or suet to get fat from them. Long-term use of the industrially derived seed oils will lead to disease. A balanced diet that includes fats from animal sources is the route to health.

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Stephen Hussey, MS, DC, is a board-certified chiropractor and functional medicine practitioner. He has a bachelor’s degree in health and wellness promotion as well as a Doctor of Chiropractic and master’s in human nutrition and functional medicine. Learn more at www.resourceyourhealth.com, or on social media @drstephenhussey.

Well Being Journal adapted this excerpt from Understanding the Heart: Surprising Insights into the Evolutionary Origins of Heart Disease—and Why It Matters copyright 2022 by Stephen Hussey, MS, DC, used with permission from Chelsea Green Publishing, White River Junction, Vermont, 802-295-6300; www.chelseagreen.com. Referenced and indexed.