Cholesterol is a kind of fat that you eat as a normal part of the diet. You also produce your own cholesterol in your liver.
Cholesterol is essential in your body. It is used to produce steroid hormones (testosterone, estrogen, aldosterone, cortisol, and so on), and it is important to make our body cells flexible.
So why does cholesterol get such a bad press?
High levels of cholesterol in the blood, also known as hypercholesterolemia, has been linked with all sorts of health problems, mostly due to blood vessel damage.
You may have heard about “good” cholesterol and “bad cholesterol”, but really there is only one kind of cholesterol (a bit of an oversimplification but we don’t want to go mad here). It is where the cholesterol is found that makes it good or bad, and how much of it there is.
You may also have heard of LDL cholesterol, HDL cholesterol, total cholesterol, dietary cholesterol, endogenous cholesterol, and so on. What I thought I might do here is try to make some sense of cholesterol and why too much of it can be bad for you.
A lot of what we read about cholesterol is that we can have too much of it our diet. Some foods do contain cholesterol and that cholesterol can find its way into your bloodstream, raising blood cholesterol levels.
Foods high in cholesterol include eggs (especially the yolks), some fish and seafood, pate, butter and cheese. Dietary cholesterol is absorbed through the walls of the small intestine (like most types of food), and the amount absorbed varies from person to person.
Most foods digested and absorbed through the walls of the intestine are absorbed directly into the bloodstream. This is because they are water soluble and can be carried easily in the blood.
Fats, such as cholesterol, are a bit different. If fats were absorbed directly into the blood they would clump together into globules that could potentially block blood vessels (this is called fat embolism). Think, “oil and water don’t mix”.
Lipoproteins carry fats in the blood
So fats have to be carried differently in the blood. Fats from the diet, including cholesterol, are packaged into little capsules called lipoproteins.
The lipoprotein particles provide a waterproof coat that stops the the fats sticking to other fats in the blood, and an “address” for the fat to be delivered to. Imagine a little envelope containing sticky fat with the address written on the outside.
These lipoproteins containing fats have different names depending on where they are made and where the fats are being delivered to. Understanding the different types of lipoprotein particles can help us to make sense of “good” and “bad” cholesterol, so I will provide a simplified overview here.
Fats absorbed from the diet through the intestines are packaged in the walls of the intestines into lipoprotein particles called chylomicrons (that’s the most exotic name – the other names are named by how much they weigh).
Chylomicrons deliver the fats from the diet to the liver. The liver repackages the dietary fats, together with fats made in the body (we’ll get to that later), into lipoprotein particles called Very Low Density Lipoproteins (VLDL). VLDL contains cholesterol and other types of fat.
The VLDL carries the cholesterol and other fats in to blood and delivers the other fats to organs of the body. After the VLDL drops off the other fats there is mostly Cholesterol left behind in these lipoprotein particles. Now they are called Low Density Lipoproteins (LDL). Heard of that one?
In the interests of your sanity I have missed out some stages here, and the main points needed to understand cholesterol transport are focused on.
When you have your blood cholesterol measured, one of the numbers you are given is your LDL cholesterol level. This LDL cholesterol is what is often referred to as “bad cholesterol”.
LDL cholesterol levels are important because these LDL particles are quite “leaky” and cholesterol is deposited on the blood vessel walls. Cholesterol, remember, is not water soluble so it sticks to blood vessel walls. It then gets inside the vessel wall cells and builds up forming plaques that lead to atherosclerosis.
These plaques narrow the blood vessel walls so that blood flow is obstructed. Also, the plaques damage the walls of the blood vessels so that blood clots form inside the vessels. Both of these are factors in development of cardiovascular disease, and increase the risk of heart attacks and strokes.
This is why LDL cholesterol is called “bad cholesterol”. High levels of LDL (containing cholesterol) means that there is a lot of cholesterol leaking out and being deposited on the walls of blood vessels, causing damage and vascular disease. The higher the levels of LDL, the more rapidly this happens.
HDL Cholesterol – it’s not all bad
Your body is prepared for these deposits of cholesterol from LDL though. Your liver produces empty lipoprotein coats that travel around the bloodstream picking up the cholesterol that leaks out of the LDL particles. This cholesterol is then taken back to the liver for disposal.
Cholesterol inside these lipoprotein particles, being taken to the liver for disposal, is called HDL cholesterol. HDL stands for High Density Lipoprotein.
HDL cholesterol is often called “good cholesterol” because it is being removed from around the blood circulation, and that protects us from vascular disease.
Endogenous cholesterol – made by your body
Your body also makes its own cholesterol in addition to the cholesterol you get from your diet. This endogenous cholesterol, as it is called, is made by the liver.
Just like dietary cholesterol that arrives at the liver, endogenous cholesterol is packaged into lipoproteins for deliver around the body via the bloodstream. Once inside these lipoproteins there is no difference between dietary and endogenous cholesterol, and high levels of LDL cholesterol lead to cardiovascular disease.
This production of cholesterol causes problems for people who try to reduce the amount of cholesterol in the diet. The less cholesterol you eat, the more cholesterol your liver makes to maintain cholesterol levels in the body.
Other fats raise blood cholesterol
You will probably be aware of the differences between saturated and unsaturated fats. Actually “lipids” is the more correct term. Lipids that are solid at room temperature are usually called fats, and lipids that are liquid at room temperature are called oils.
Saturated lipids (fats) come from animals, are solid at room temperature and increase the amount of cholesterol produced by the liver. Unsaturated lipids (oils) come from plants and reduce the amount of cholesterol produced by the liver.
So it’s not just cholesterol in your diet that can increase your blood cholesterol levels. Reducing the amount of animal fat that you eat will also help to reduce the amount of cholesterol produced by your liver, and will help to reduce the “bad” cholesterol in your bloodstream.