Cholesterol is a sterol. A sterol is a naturally occurring unsaturated steroid alcohol. Sterols are typically waxy solids, and they are part of the steroid family.
The diagram for cholesterol is below.
The reason cholesterol is called a steroid “alcohol” is because of the presence of the hydroxyl group (the “OH” group in the diagram, circled in red). This hydroxyl group is one of the main functional groups of cholesterol, and this is the site that determines whether the cholesterol is in its active form, or storage form (the storage form is called “cholesterol ester”).
Sterols are produced by all types of life, including plants, animals, bacteria, and fungi. However, cholesterol, specifically, is unique only to animals. You may have heard of phytosterols, and these are the analogs of “cholesterol” that the plant kingdom makes.
Phytosterols in brief
Our bodies can’t properly absorb phytosterols. In fact, they compete with cholesterol absorption. Phytosterols have actually been used in attempt to “lower” the cholesterol absorbed from our diet because phytosterols displace cholesterol from micelles which are the in the gut (cholesterol micelles are formed when we break down hydrophobic foods in the stomach such as fats and cholesterol). The theory goes that reducing cholesterol from the diet will reduce blood cholesterol levels and reduce risk of developing cardiovascular disease. However, these attempts don’t make much sense in light of the following two key facts:
- The amount of cholesterol we get from our diet is significantly less than the amount that is synthesized by our cells. Moreover, if our cells sense low levels of cholesterol, they will ramp up attempts to synthesize more cholesterol.
- Cholesterol and lipid-lowering therapies have NO impact on reducing the risk of cardiovascular disease.
Back to cholesterol…
Cholesterol is necessary for life. Without it, we wouldn’t have functioning cells and cellular systems. Cholesterol is one of the main building blocks of our cell membranes. It is vital for carefully controlling cell membrane fluidity, how cells interact with other cells, and how the cell transport nutrients and other compounds from inside and outside. Furthermore, cholesterol is necessary for vitamin synthesis and is the precursor to sex hormones (progesterone, testosterone and estradiol) and bile acids. In short, your body NEEDS cholesterol. It is necessary for life. And it is a good thing.
In fact, lack of cholesterol can cause malnutrition. Furthermore, individuals with Smith-Lemli-Opitz syndrome have genetic mutations that prevent them from properly synthesizing cholesterol, and this can lead to mental disabilities and skeletal muscle issues.
Overall, there is no such thing as good or bad cholesterol. Cholesterol wrongfully gets a bad rap for being a culprit of atherosclerosis and cardiovascular disease because it is present in atherosclerotic plaques. However, cholesterol itself is not to blame. To date, evidence does NOT support a link between dietary cholesterol and cardiovascular disease.
The only time cholesterol is “bad” is when it ends up in a place where it doesn’t belong, like an artery wall, during periods of inflammation. When this occurs, it can initiate the process of atherosclerosis. This is not the normal fate of cholesterol, however. Atherosclerosis only occurs in states of inflammation where cholesterol ends up in the wrong places.
How and why does cholesterol end up in the wrong places? In short, metabolism and epigenetics play a big role. However, this will be discussed in detail in a later post. In the meantime, stay tuned!
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