How Cholesterol ACTUALLY Works In Your Body

Added: 2026-05-31

[00:00:00]Cholesterol might be one of the most misunderstood molecules in the entire human body. Because most people have heard that high cholesterol is dangerous, that LDL is the bad cholesterol, and HDL is the good cholesterol, and that cholesterol can clog your arteries and lead to heart attacks and strokes. But at the exact same time, cholesterol is also absolutely essential for human survival.

[00:00:23]Your liver actually manufactures cholesterol on purpose because [music] you cannot survive without it. So, if cholesterol is so important for survival, then why is it also associated with cardiovascular disease? And why do some people with elevated cholesterol develop plaques in their arteries while others don't? And I actually think that due to this confusion surrounding cholesterol and how it can silently have a significant impact on your long-term health that this is going to be one of our more important videos because we are going to talk about what cholesterol actually is. What's the difference between HDL, LDL, and even some other markers you may have heard about like apo B and LP little A? We'll also discuss how eating cholesterol and other fats actually influences your cholesterol levels, how your body absorbs and transports cholesterol, and of course, when does cholesterol become a problem and form plaques in your arteries, and is there anything you can do to keep your levels in check and reduce your risk of developing cardiovascular disease? It's going to be an important one. So let's jump into this anatomical and physiological awesomeness.

[00:01:30]Now before we can understand how cholesterol contributes to diseases such as atherosclerosis in the arteries, we first need to understand what cholesterol actually is. Because cholesterol is not an inherently bad molecule. In fact, as I said, cholesterol is absolutely essential for human survival. Chemically speaking, cholesterol is a type of lipid molecule known as a sterile. And as an FYI, fats are probably the most common type of lipid that you've heard of. But steriles, which cholesterol is, is just another type of lipid. Now, one of the major characteristics of lipids is that they are hydrophobic. Hydro meaning water and phobic referring to fear. So, this means that lipids do not mix very well with water. And that detail is going to become extremely important later on in the video. But first, let's talk about what cholesterol actually does inside your body. One of cholesterol's biggest roles is helping build and maintain cell membranes. Every single cell in your body is surrounded by a cell membrane, primarily made of phospholipids. But cholesterol is also embedded within those membranes, helping regulate things like membrane fluidity and providing structural stability. But cholesterol doesn't stop there.

[00:02:37]Cholesterol also is used to synthesize steroid hormones. hormones like testosterone, estrogen, cortisol, progesterone, and aldoststerone. All of these are ultimately synthesized from cholesterol. Your body also uses cholesterol to help produce bile salts, which are components of the bile that is produced by the liver that you can see on this body. But this body doesn't have a gallbladder, and the gallbladder actually stores the bile. So, we'll show you a gallbladder over on this body that you can see right here, this little bag-like organ just underneath the liver on this body. And bile is extremely important for digesting dietary fats.

[00:03:13]Cholesterol is also involved in vitamin D synthesis. And your nervous system even uses cholesterol to help build myelin sheaths around neurons, which is this fatty insulation surrounding the axons of neurons, which helps electrical impulses travel rapidly throughout the nervous system. So, as you can see, cholesterol is not some foreign invader entering the human body. It is a molecule your body intentionally manufactures because it is necessary for multiple physiological functions. And this brings up another major point of confusion because many people think cholesterol only comes from food. But your body actually synthesizes cholesterol on its own because again your liver is constantly producing cholesterol and your body is so dependent on cholesterol that even if you ate very little dietary cholesterol your body would still continue to manufacture it. Now, that does not mean diet is irrelevant because nutrition can absolutely influence cholesterol levels and cardiovascular risk, which we'll discuss in a little bit. But what it does mean is that cholesterol is not simply something you just put into your body. Your body actively creates it in order to survive. But now we run into an interesting problem. Remember I said that cholesterol is hydrophobic. It does not mix well with water. But our blood is mostly water. So, your body needs a specialized system to transport cholesterol throughout the body. And this is going to eventually lead us to things like HDL and LDL particles that you may have heard called HDL and LDL cholesterol, which we'll also talk about that nuance in the names a little bit later on as well. But we first need to figure out how the body transports cholesterol. And this includes the cholesterol that is synthesized by the liver as well as the cholesterol that we eat. So, let's start with the cholesterol that we eat. That could be cholesterol in eggs, meat, dairy products, or some other animal-based food because dietary cholesterol is only found in animal products. But once swallowed, cholesterol will travel down the esophagus, which here's an esophagus that we've removed from one of the bodies. But just to orient you a little further, here is the larynx or Adam's apple, which would be right here on me.

[00:05:19]The windpipe or the trachea is below the larynx, and behind the trachea, we have the food tube or the esophagus. But once the cholesterol travels down the esophagus, it will enter into the stomach that you can see here. Now, interestingly, the cholesterol molecule itself is not heavily digested in the stomach as it's already a relatively small lipid molecule. So, it doesn't need to be broken down into tiny subunits the way proteins or carbohydrates do. And so, the cholesterol molecule itself mostly survives this process intact. But eventually it will move from the stomach and into the small intestine. And this is where things start becoming really interesting because remember cholesterol is hydrophobic. It does not mix well with water. And the inside of the small intestine is a watery environment. So your body needs a way to help transport and absorb cholesterol and other lipids.

[00:06:12]And this is where bile becomes extremely important. bile produced by the liver and the gallbladder that we saw earlier that we can see again here is going to be released into the small intestine. So liver gallbladder dump their bile into the small intestine and bile contains bile salts which are amphopathic molecules which is a fancy pants way of saying that one side interacts well with water which would be the hydrophilic side while the other side interacts well with lipids which would be the hydrophobic side. And so this allows bile salts to almost act like biological detergents and they begin surrounding these dietary lipids bundling them into tiny transport clusters called myels.

[00:06:55]Now my cells can contain many different types of lipids including cholesterol.

[00:07:00]But they also contain fatty acids, monoglycerides, phospholipids and fats soluble vitamins. And this process is incredibly important because these hydrophobic molecules, these hydrophobic lipids, which would otherwise struggle to move efficiently through the watery environment of the small intestine, but instead they are contained within the hydrophobic portion of the myel. And the myel essentially acts like a delivery vehicle that helps shuttle these lipids toward the absorptive cells lining the small intestine. And these absorptive cells are called interosytes which is a great name because interero refers to intestine and site means cell. Now an important detail here is that the myel itself is not what gets absorbed into the interosite. Instead the myel brings these lipid molecules close to the brush border or the surface of the interosite where substances like cholesterol can be moved into the cell by certain membrane transporters. But once cholesterol enters the interosite, something very interesting happens. The cholesterol gets repackaged together with triglycerides and other lipids into a massive lipoprotein particle called a kyomicron. And these kyomicrons are absolutely loaded with lipids. In fact, they are so large that they cannot enter the normal blood capillaries. Now normally the nutrients that you digest, the amino acids from the proteins you eat or the glucose from the carbs you eat, normally these nutrients will move from the interosite into the bloodstream and then go directly to the liver. But because the kyomicrons are so large, they have to take a different route. And what they do is that they enter larger specialized lymphatic capillaries called lactals. So the cholesterol and other lipids you ingest actually bypass the bloodstream and the liver initially and instead enter your lymphatic system but they will eventually get to the bloodstream. They just have to take this little detour because of the size of the kyomicron that they are residing in. So the kyomicron will move from the lactals into larger lymphatic vessels that are near the small intestine. then move into the largest lymphatic vessel in the human body called the thoracic lymphatic duct. And finally, this thoracic duct will empty these kyomicrons into a [music] vein just under your left clavicle. Well, technically at the junction of the left subclavian vein and the left jugular vein. But the point is that we have finally now got this kyomicron into the bloodstream. Now once the kyomicrons finally enter circulation, their main job is to begin delivering triglycerides to tissues throughout the body. But remember they also contain cholesterol and other lipids. And as these kyomicrons circulate through capillary beds in tissues like skeletal muscle, cardiac muscle and atapose tissue, they encounter an enzyme called lipoprotein lipase. And this enzyme begins breaking down triglycerides within the kyomicron into free fatty acids that can either be burned for energy or stored for later use. And as triglycerides are gradually removed from the kyomicron, the kyomicron becomes smaller and denser.

[00:10:10]And because much of the triglyceride content has now been removed, the remaining kyomicron becomes proportionally richer in cholesterol.

[00:10:19]Eventually, it transforms into what is known as a kyomicron remnant. And these remnants will eventually travel to the liver where they'll be taken up and processed. So, just to review that, we have these large kyomicrons that have just entered the bloodstream from the lymphatic system and they contain triglycerides, cholesterol, and other lipids. And as they travel through the bloodstream, tissues are going to pull triglycerides out of the kyomicron to use for energy or energy storage. And so the kyomicron is getting smaller and smaller until it is mostly left with cholesterol inside. And this smaller kyomicron with the leftover cholesterol is called a kyomicron remnant. And this again will make it to the liver. Now one of the main points of today's video is how cholesterol and carriers like LDL and HDL particles relate to your long-term cardiovascular health. And one of the scary things about cardiovascular disease is that it can develop silently over years or even decades before symptoms even appear. And because of that, biomarkers related to cholesterol, inflammation, and metabolic health can become extremely important because they can give us insight into what may be happening physiologically long before somebody develops something like a heart attack or stroke. And this is actually where the sponsor of today's video comes in, Rhythm. Rhythm is an atome blood testing service that allows you to monitor multiple biomarkers related to cholesterol, cardiovascular health, inflammation, metabolic health, and hormones, all from home. And one thing I actually think is interesting is that many people only get blood work done maybe once a year during a physical. But physiology is dynamic. Things like diet, exercise, body composition, sleep, medications, and metabolic health can all influence biomarkers over time. Now, the actual testing process is surprisingly simple. You basically peel, stick, and click the device onto your upper arm. And that little click is completely painless. And within a minute or so, the collection tube begins to fill with blood. And from that sample, they can analyze biomarkers related to things like LDL, HDL, triglycerides, APOB, inflammation markers, and more.

[00:12:19]Then once the tube is filled, you simply remove it, snap the cap on, mix it around a few times, and then they'll even pick it up from your house. And I also like that this gives people a way to follow trends over time because cardiovascular and metabolic health is usually not about one single perfect decision. It's often the cumulative effects of physiology and lifestyle over long periods of time that matter most.

[00:12:40]So, if you're interested, go to rhythm.help/ha and get free shipping on your first month with Rhythm. That link and information will also be in the description below. And now, let's get back to the video. Now, once these kylo micron remnants are in the liver, the liver essentially unpacks them and decides what to do with their lipid contents. In many ways, the liver acts like the central command center of cholesterol metabolism. And the liver is not just removing cholesterol. Remember, the liver is constantly synthesized in cholesterol, but it also recycles and packages cholesterol. The liver can also convert cholesterol into bile salts, and those bile salts can then be secreted into the bile and eventually released into the small intestine to help digest dietary fats, and we discussed that earlier. But the liver can also directly secrete cholesterol into the bile. Now, keep in mind, those are two different things. converting cholesterol in order to make bile salts versus just secretreting cholesterol directly into the bile without converting it. And secretreting cholesterol directly into the bile is one of the ways the body can help eliminate excess cholesterol because as we already know, bile will eventually enter the digestive tract.

[00:13:54]And as a fun little FYI, components of bile help contribute to the normal brown color of stool. And I actually remember one of my first weeks working in the urgent care right when I got out of school, I had a patient that came in because he was having what he described as white colored poop. And this was an indicator that something was going on with his liver, gallbladder, andor the bile ducts. And one more interesting FYI if I may. If bile becomes too saturated with cholesterol, cholesterol can eventually precipitate out and contribute to the formation of cholesterol gallstones, which is the most common type of gallstone. But coming back to the liver, because the liver also has another major job, probably the one that you've all been waiting for. It needs to transport lipids back out into the bloodstream so they can be delivered to the tissues throughout the body. And this is where we start getting into things like VLDLDL, LDL, and HDL particles. But you might be wondering, if the liver just received all of these cholesterol rich kyomicron remnants from the bloodstream, then why is it repackaging lipids such as cholesterol and triglycerides and sending them back out into the bloodstream again? Well, remember the cells throughout the body are constantly active and still need triglycerides, cholesterol, and fatty acids. They don't just need them right after a meal. Plus, you may not have eaten a cholesterol or lipid-rich meal. So, you may need to make cholesterol in the liver and send it out to the tissues. So, the liver is going to have to repackage these hydrophobic molecules into particles that are similar to kyomicrons. And the first particle that we need to learn is VLDDL which stands for very low density lipoprotein. And much like kyomicrons, these VLDL particles do contain cholesterol, but they are more heavily loaded with triglycerides. So once they enter circulation, they can again interact with lipoprotein lipase in capillary beds throughout the body, allowing triglycerides to be removed and delivered to the tissues. But as triglycerides are gradually removed from these VLDLDL particles, the particles begin changing and similar to what happened with kyomicrons, they become smaller, denser, and relatively richer in cholesterol. And over time, VLDLDL particles are gradually transformed into IDL particles, which stands for intermediate density lipoproteins. And as more triglycerides are removed, they continue to get even smaller and then become LDL particles, which stands for low density lipoproteins. And this is where we arrive at one of the most misunderstood topics in all of cardiovascular physiology. Because LDL is often called bad cholesterol, but LDL is not actually cholesterol itself. LDL is a lipoprotein particle that transports cholesterol through the bloodstream. And this is why calling it an LDL particle rather than LDL cholesterol is more physiologically accurate. And physiologically LDL particles do serve important functions because tissues throughout the body still need cholesterol for things like cell membranes, hormone synthesis and other cellular functions. And so these LDL particles will transport the cholesterol to these tissues. Now later in this video we are going to talk about how LDL particles can contribute to atherosclerosis and cardiovascular disease. But one of the reasons we went through all of these details is because it's important to understand that LDL particles were not created by the body to cause cardiovascular disease. They are part of a normal physiological transport system designed to transport lipids throughout the body. But LDL is not the only major lipoprotein particle involved in cholesterol transport. Your body also has HDL particles which stands for highdensity lipoproteins. And the reason these particles are called highdensity or lowdensity lipoproteins is because they contain different proportions of lipids and proteins. LDL particles have a higher proportion of lipids compared to proteins. And since lipids are less dense than proteins, they're referred to as low density. But HDL particles contain a higher proportion of proteins compared to lipids and therefore are high density.

[00:18:17]And while LDL particles are largely involved in transporting cholesterol out to the tissues throughout the body, HDL particles are heavily involved in transporting cholesterol back toward the liver. And this process is often referred to as reverse cholesterol transport. So you can almost think of LDL particles as delivering cholesterol outward to tissues while HDL particles help participate in bringing some cholesterol back towards the liver where it can be recycled, repackaged or eliminated. And it is also thought that HDL particles may have some antioxidant and anti-inflammatory functions. And this is why some people often hear HDL referred to as the good cholesterol while LDL is referred to as the bad cholesterol. But as we're going to see, the real physiology is much more nuanced than simply good versus bad. LDL is sometimes referred to as bad cholesterol because it is considered atherogenic.

[00:19:11]You may have heard of atherosclerosis and this refers to the formation of plaques within the arteries. And if something is atherogenic, that means it can contribute to atheroscllerosis aka the formation of plaques within the arteries. And plaques building up in the arteries will narrow them and can eventually lead to conditions such as heart attacks and strokes. And LDL particles do this because under certain conditions they are able to enter the wall of the artery [music] and more importantly be retained in the wall of the artery. And we could go crazy going into all the details of atherosclerosis and what happens once LDL is retained in the wall of the artery. But the summarized version is that it will trigger oxidation, inflammation, the formation of these puffy foam cells, and ultimately the formation of a plaque.

[00:19:58]And as more and more LDL and other aogenic particles get retained, it can lead to larger and larger plaque formation. However, LDL is not the only agogenic particle. It's just the most popular one, I guess you could say.

[00:20:13]There are also other aogenic lipoproteins some of which we have already mentioned such as VLDLDL particles, IDL particles and even remnant particles as well as lipoprotein A also known as LP little A. Now you might wonder what about these particles makes them capable of being aogenic or in other words why are they more likely to be retained in the wall of the artery and form plaques? Well, one thing all of these aogenic particles have in common is that they contain a protein called apollo lipoprotein B, also known as apo B. So LDL, VLDLDL, IDL, remnant particles and LP little A contain apo lipoprotein B on their surface whereas something like HDL does not. And apo has structural characteristics that allow it to bind to molecules within the arterial wall, especially molecules called proteoglycans. And when it binds to these molecules, it causes the particles to get stuck or retained within the arterial wall and contribute to this process of atheroscllerosis or plaque formation. Now you may not have caught this, but I did say LDL particles as well as the others can be atherogenic under certain conditions. We've already learned that our body naturally makes all these particles for the purpose of transporting lipids throughout the body, not for creating plaques. So what conditions tend to make these particles become aogenic? Well, something extremely important to understand is that plaque formation is usually not caused by one single thing.

[00:21:51]Atherosclerosis is typically a multiffactorial process, meaning there are often multiple conditions and risk factors interacting together over many years or even decades. But if we did have to somewhat simplify this explanation of what most often leads to plaque formation, we'd see two main contributors. An abnormally high amount of these aogenic apo containing particles, plus damage and dysfunction to the endothelium. The first one you've likely heard the most about because all of us have heard in some form or fashion that we want to keep our cholesterol levels down. But we all know the nuances of this now. And what we specifically want is to keep the levels of these cholesterol carrying particles down especially those apo particles of LDL, VLDL, IDL, LP little A. Now genetics can play a major role on how many of these particles circulate in your body. like some individuals inherit conditions that cause extremely elevated LDL particle levels or abnormal lipoprotein such as elevated LP little A which can significantly increase cardiovascular risk even in relatively healthy individuals. But there are also controllable lifestyle factors that we can modify to help lower the levels of these particles which we'll address in just a minute. But let's come back to the other main factor that influences plaque formation and that was dysfunction and damage to the endothelium. The endothelium is the inside lining of your arteries. And under healthy conditions, the endothelium helps regulate vascular tone, blood flow, inflammation, and what substances move into and out of the arterial wall. But certain conditions can damage or stress this lining over time, making the arteries more susceptible to retention of these aogenic particles. For example, hypertension or chronically elevated blood pressure places increased mechanical stress on the endothelium.

[00:23:47]Smoking introduces oxidative stress and inflammatory chemicals that can damage the endothelium. Diabetes and insulin resistance can contribute to chronic inflammation and metabolic dysfunction with elevated blood glucose levels. also being able to damage the endothelium.

[00:24:03]Obesity, sedentary lifestyles, poor sleep, chronic stress, and certain dietary patterns may also contribute to inflammatory and metabolic conditions that increase cardiovascular risk. And ultimately, all of these things can contribute to damage and dysfunction of the endothelium of the artery, making it again more likely to retain those agenic particles. And again, this is a cumulative process influenced by both the number of circulating aogenic particles, the LDL, LDL, all those wonderful things that we just talked about and or those APOB containing particles and how long your arteries are exposed to them over the course of years and decades plus the presence of endothelial dysfunction, inflammation, and metabolic disease. So, in summary, I kind of like to think of it like this.

[00:24:51]At normal levels, LDL, VLDLDL, IDL, and LP little A particles circulate throughout the blood doing their job of lipid and cholesterol transport without causing much of a problem. But if those levels start to elevate, that increases the risk that some of them might start to get retained or embed within the wall of the artery. Then if you also add damage and inflammation to the endothelium, the particles are even more likely to get stuck and bind to these damaged and inflamed areas of the arterial wall. So the next question becomes, what can we do to prevent this or at least reduce our risk of major plaque formation? Well, in general, we can try to influence both sides of that equation. Meaning we can try to reduce the amount of circulating aogenic particles while also trying to reduce the damage, inflammation and dysfunction involving the endothelium. And this can be done with medications as well as lifestyle modifications. Now I won't go too crazy with medications, but probably the most well-known medications for this are statins. And statins primarily work by reducing cholesterol synthesis within the liver. But they also lower LDL levels by increasing LDL receptor activity on liver cells which allows the liver to pull more LDL particles out of the bloodstream. And for certain individuals, these medications can dramatically reduce these levels. But lifestyle modifications can also have major effects on both circulating aogenic particles and endothelial health. And let's start with diet because this is where a lot of confusion exists. One important thing to understand is that dietary cholesterol itself often has a smaller effect on blood cholesterol levels than many people think. And it's actually diets very high in saturated fats that have a greater influence on increasing LDL particle levels. Although genetics can strongly influence how dramatically a person responds to this. And the simplified explanation for why this occurs is that saturated fats can influence how the liver regulates cholesterol metabolism and LDL receptor activity, which can reduce the liver's ability to remove LDL particles from the bloodstream. Diets high in refined carbohydrates and excess calories can also contribute to obesity, insulin resistance, elevated blood glucose levels, elevated triglycerides, and increased production of triglyceride rich lipoproteins such as VLDL particles, which remember eventually become LDL particles. On the other hand, diets rich in fiber can help reduce cholesterol absorption and increase cholesterol elimination through the digestive tract. Exercise is also incredibly important because regular physical activity can improve insulin sensitivity, metabolic health, blood pressure, body composition, endothelial function, and overall cardiovascular health. Exercise may also help improve triglyceride levels and lower some of those aogenic particles over time. And remember, one of the major concepts we discussed earlier is that plaque formation is not just about those aogenic particles themselves, but also the health of the endothelium. So anything that contributes to chronic inflammation, oxidative stress or endothelial damage can potentially increase cardiovascular risk. And this is why smoking sessation is so important because smoking contributes heavily to oxidative stress and endothelial dysfunction. Similarly, managing blood pressure to take the mechanical strain off the endothelium is also very important. But also improving sleep, reducing chronic stress, maintaining a healthy body composition, and improving metabolic health can all help reduce stress and dysfunction involving the vascular system over time. And importantly, this is usually not about making one perfect decision.

[00:28:33]Cardiovascular disease often develops cumulatively and silently over decades, which means small improvements consistently maintained over long periods of time can meaningfully reduce risk. And so this means you want to stay on top of this with your annual physicals as well because the only way for you to know if you have elevated aogenic particles is by getting a lipid panel done which many people refer to as their cholesterol tests. The typical lipid panel includes your triglyceride levels, LDL cholesterol, HDL cholesterol, and total cholesterol with some panels also estimating VLDL levels.

[00:29:09]But clinicians will also add some additional tests like APO B or even LP little A depending on results of the initial testing as well as your individual risk factors. But I hope one of the biggest takeaways from this video is that cholesterol itself is not inherently bad. Your body absolutely requires it for survival because as we've learned, cholesterol is necessary for cell membranes, hormone synthesis, bile production, vitamin D synthesis, and nervous system function. The real issue is excessive exposure to high amount of aogenic particles combined with conditions that promote endothelial dysfunction, inflammation, and plaque formation over many years and decades.

[00:29:49]So the goal is not to eliminate cholesterol from the body entirely. The goal is to reduce excessive exposure to aogenic particles while also protecting the health of the arteries themselves.