In the last post, we spoke about the lipid hypothesis and how it came to be. In this post we will be looking at why saturated fat and cholesterol having being wrongly accused of the main drivers behind heart disease (HD).
Poor diet and lifestyle, the real causes of heart disease
If you have been told by your doctor that your cholesterol is high from a blood test, I’m sure you have all seen on your test the number values relating to your LDL and HDL cholesterol levels.
Cholesterol is just a molecule and HDL and LDL are not different types of cholesterol. Rather, they are carriers of cholesterol. Think of them as vehicles that transport cholesterol in your blood stream. Cholesterol is a fatty molecule and in order to travel through the blood, which is mostly water, it needs a carrier.
So if you imagine your blood vessels as a highway, with LDL and HDL being the cars and cholesterol being the passengers in the cars. LDL’s main function is to carry cholesterol from the liver to all the different tissues in the body where it is needed to perform its metabolic functions. HDL on the other hand is responsible for taking unused cholesterol away from the tissues and back to the liver to be excreted.
This is why HDL is considered protective against heart disease as it helps remove excess cholesterol from the blood. Where is LDL carries cholesterol into the blood. This is also why HDL is called “good” cholesterol and LDL as “bad” cholesterol. HDL and LDL are neither good or bad, they are just part of physiological functions in the body. However, in saying that, high LDL cholesterol levels on a blood tests are associated with heart disease, which is why it is called “bad,” but this association will be explained below.
Moving back to the car, highway and passenger analogy. On the road we can have either busses or cars. Obviously busses carry more people, therefore you may have a lot of people travelling on the road, however they may all be in busses. This will in turn decrease traffic. Where is if all these people were put into individual cars, this would increase traffic on the highway.
If there is more traffic on the road, there is more likely to be a crash and once this happens, there is more likely to be a build up of traffic. Similarly, if there is more LDL in your blood, the more likely that these particles will crash and causes blockages in your blood vessels, leading to decreased blood flow. There are different types of LDL in your blood. Large ones and small ones. The large ones would represent the busses and the small ones would represent the cars. Obviously, we would want more busses than cars, larger LDL than small.
When these LDL particles (busses or cars) crash into your blood vessels, the cholesterol passengers will obviously be found at the crash scene, however this does not mean that cholesterol (passengers) was the cause of the crash. It may have been the driver or something else on the road. The presence of cholesterol in blood vessel walls of people who have had a heart attacks or strokes, has led to further blame of cholesterol being the driver of HD.
Ultimately, the liver will rarely overproduce cholesterol, it just depends what type of vehicle this amount of cholesterol (passengers) is travelling in, busses (large LDL) or cars (small LDL).
What can often happen is that the LDL particles floating in the blood don’t gwt taken up by there target tissue to drop off what they are carrying. This leads to LDL lingering in the blood for longer than it should, increasing the risk of it crashing and causing a plaque in the arteries. Going back to our analogy, this can be interpreted as a lack of parking on the road, which ends up increasing traffic on the as the cars and busses can’t park and drop off their passengers. Over time this will increase passengers and vehicles on the road, increasing the risk of crashes and traffic.
Based on this information, it is not about how much cholesterol is in your blood, it is about how many LDL particles are in your blood and whether they are large (busses) or small (cars). The factors that cause a lack of parking spaces and increased amount of cars rather than busses, will be discussed below.
Saturated fat increases busses not cars, therefore it is not associated with HD
Just looking at your LDL levels on a blood test will not tell you whether or not your cholesterol is in cars or busses. Sometimes it may be high, but if it is all in busses than this is more protective against HD, as it means there is less traffic.
This is where ratios come in. Ratios help to determine particles sizes of LDL in the blood and are a more sensitive marker of HD risk on your blood tests. This will be discussed below.
in uncontrolled/poorly done feeding studies, saturated fat consumption may be associated with heart disease and increased cholesterol levels because often these studies have people eating cholesterol rich foods without other anti-oxidants like fruit and vegetables, as well as with unhealthy foods like vegetable oils and processed carbs (e.g. burgers).
However, in consistently controlled studies, it is no doubt that eating a diet high in cholesterol and saturated fat will also increase cholesterol (passengers) levels in the blood such as LDL and even HDL. However, despite this, it does not increase the actual risk of having a heart attack, a stroke or some kind of cardiovascular event.
Why is this you may ask?
Well, maybe it has something to do with the fact that saturated fat may increase passengers, but it also increases busses carrying these passenger and not cars. Saturated fat may also be less prone to causing LDL particles to crash. You could think of saturated fat maybe increasing good drivers. Lastly, saturated fat may help busses (LDL) to find parking spaces (tissue receptors).
Where is in controlled feeding studies, if you replace saturated fat for vegetable oils, there is a dramatic increase in the risk of actual cardiovascular events. This may be because that vegetable oils increase the number of cars on the road and decrease parking spaces, leading to more LDL particles floating in the blood.
(Note: Vegetable oils are easily oxidized and create inflammation the body. They are used as cooking oils in restaurant/takeaway foods and found in all packaged foods, sauces and salad dressings. They not only increase heart disease risk but the risk of other diseases as well).
The fact that saturated fat increases blood cholesterol and LDL levels, but not HD risk, it shows that simply looking at these values on a blood test is not a good marker of HD risk. This is because these values tell us nothing about the size of LDL particles.
In the last article of this series we will discuss how to analyse a standard blood test to asses your HD risk.