I first want to give Dr. Nadir Ali credit for most of the research in this particular post.
All living things have some form of a “sterol” that fulfills vital functions in its body. Animals have cholesterol and plants have phytosterol. One of the most important functions of these molecules is the structure and integrity of the cell membrane of the organism. Phytosterol does this in plants and cholesterol does this in animals. Right off the bat it is interesting to think that if animals use cholesterol and humans are animals, then do we think that cholesterol or phytosterol would be better for humans? Obviously, cholesterol is better.
Most humans eat both forms of these sterols because most humans eat an omnivorous diet. However, we eat these two sterols together, they actually compete to get absorbed in the intestines. Humans are very well designed to absorb fat because of our very developed gallbladder, this is a characteristic we share with known carnivores. Since our 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. They do this by surrounding the fats in what is called micelle and shuttling them to where they need to go.
One interesting observation is that many times people supplement Vitamin D but do not see a rise in blood levels of the vitamin. This is likely due to the fact that they did not eat a meal with fat in it when they took the vitamin D. Without eating the fats, no bile was stimulated to be secreted and not much fat was absorbed. Since Vitamin D is fat soluble (transported in fats) then it is likely not getting absorbed either.
Now, by eating both phytosterols and cholesterols the body attempts to absorbs both types of fat. Obviously in this case the absorption is split between the two. This competition often resulted in less absorption of cholesterol and therefore decreases blood levels of cholesterol. This was one reason that plant sterols (margarine, vegetable oils) were recommended by heart health regulating bodies and associations. Interestingly, in the case of phytosterols the gut has a mechanism that places as much of the phytosterols it absorbs back into the intestines in the hopes that it gets eliminated with the other waste. In other words, the body doesn’t want it.
There is a genetic condition where this mechanism that puts absorbed phytosterols back into the intestines is not present. This condition is called sitosterolemia. The condition is characterized by phytosterol deposits like xanthomas (deposits in skin) or xanthelesma and arcus senilis (deposits in eyes). These people 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 them to clump up. They 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 inability of the body to get rid of the phytosterols efficiently, but the more problematic symptoms are due to the effects of phytosterols on red blood cells. Red blood cells are shaped like a disc with a slight depression in the middle making them look sort of like a doughnut. They are able to maintain this shape because they have cholesterol in the cell membranes. When there are too many phytosterols around and not enough cholesterol the red blood cells have to use phytosterol for the cell membranes instead. When this happens the red blood cells lose their pliability 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.
Hopefully you are starting to see the problems that can happen from the consumption of too many plant sterols. Let’s look at some studies. In the first study they gave two groups of rats either an animal fat diet or that diet plus phytosterols. In the animal fat diet, the rats arteries stayed dilated while in the phytosterol group their arteries became restricted. Also, in this study they induced a stroke in the rats. In the rats eating high animal fats the stroke was much smaller than in the group that had the phytosterols added to their diet. The phytosterols present in the red blood cells made the strokes bleed more. As a second part of the study they looked at people who needed replacement heart valves. They had data on these patients on how much plant sterol rich foods they consumed. When they removed the old valves, they found that those who ate the most plant sterol foods had the highest amount of plant sterols deposited on the heart valves contributing to their need of a replacement. (1)
In another study in rats, researchers took rats genetically altered to be prone to stroke and fed one group of the rats a high animal fat diet, one group a diet high in corn oil, and a third group a diet high in olive oil (corn and olive oil both having phytosterols). They then waited to see which group lived longer. The group of rats that at the high animal fat diet lived much longer than the other groups. (2)
By now you probably realize that large amounts of these plant sterols in your diet is not a good idea. But before we discuss the main sources of these phytosterols there is one other way we can accumulate more of them other than just eating them. Like we said before the body tries to get rid of as many of these plant fats that it absorbs by putting them back into the intestines. However, if there is too many of them and it overwhelms this mechanism then we end up with way more absorption. Interestingly, in one study they gave people high doses of statins and over time the amount of plant sterols absorbed continued to increase. (3) By interfering with the production of cholesterol it prevents the reabsorption of it in the liver and therefore more plant sterols are absorbed instead. Just another reason not to take statin drugs.
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). The seed oils are way higher in these plant sterols that any of the other plant fats and it is no wonder that we have seen a steady increase in heart disease since seed oils were mass produced and became widely available in the early 1900’s. While olive oil, avocado oil, and coconut oil do have plant sterols, they are in much smaller amounts than the seed oils and I believe a safer option if you are going to eat plant fats.
All this information goes to show that humans are designed to eat and use animal fats, but we can use plant fats to survive when animal fats are not available. Plant fats are not ideal, and long-term high use of them can lead to many health problems. We need to stick to fats that come naturally from animals. You don’t have to over process lard, beef tallow, butter, bone marrow, or suet to get a fat from it because it is naturally in it's ideal form for us. These natural fats are the route to health and long term use of the industrially derived seed oils and plant fats will lead to disease.
Stay healthy out there!
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