What are Lipoproteins? Lipoproteins are special particles made up of droplets of fats surrounded by a single layer of phospholipid molecules. Phospholipids are molecules of fats which are attached to a phosphorus- containing group. They are distinctive in being amphipathic, which means they have both polar and non- polar ends. In a lipoprotein, the polar ends of all the phospholipid molecules face outwards, so as to interact with water, itself a polar molecule. This enables the lipoprotein to be carried in the blood rather than rising to the top, like cream on milk. The non- polar fat balled up inside the phospholipid layer, at the center of the lipoprotein, is thus transported to the place where it must be stored or metabolized, through the bloodstream, despite being insoluble in blood. Thus lipoproteins are molecular level trucks to carry fats wherever they are required or stored. Copyright: Naeblys via Shutterstock, Image ID: 1. Types of lipoproteins. Different lipoproteins are differentiated based on specific proteins attached to the phospholipid outer layer, called the apolipoprotein. This also helps to make the fatty molecule more stable, and also binds to cell surface receptors in some cases, to enable the cell to take up the lipoprotein by receptor- mediated endocytosis. The types of lipoproteins with their function are as follows: Chylomicrons – these are the largest and least dense of the lipoproteins, with the highest triglyceride content. They consist of a protein component synthesized in the liver, which wraps around diet- derived cholesterol and fats. It travels from the intestinal lymphatics to the large veins, and sticks to the inner surface of the tiny capillary blood vessels inside the muscles and the fat storage cells in various parts of the body. There the fat is digested, while the cholesterol remains. This is now called the chylomicron remnant. It travels to the liver, where the cholesterol is metabolized. Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein. These groups, from least dense, compared to surrounding water, (largest particles) to. Very-low-density lipoprotein is especially harmful because is made up of even more triglycerides, a type of fat, than low-density lipoprotein and thus further. Thus chylomicrons deliver fats and cholesterol from the intestines to the muscles, fat cells and the liver. VLDL, very low density lipoprotein – this is composed of protein, fats and cholesterol synthesized in the liver. It is associated with 5 different apoproteins, namely , B- 1. C- I, C- II, C- III and E. It is converted to IDL and LDL by removal of the apoproteins, except for one called apoprotein B1. They are second only to chylomicrons in the percentage triglyceride content. IDL – intermediate density lipoprotein, is created by the metabolism of VLDL. LDL, low density lipoprotein – this is the last VLDL remnant, and contains chiefly cholesterol. The only apoprotein associated with it is apo. B- 1. 00. Thus all these forms carry fats and cholesterol produced in the liver to the tissues. AST or SGOT. One of the two main liver function blood serum tests (the other being the ALT test). The purpose of this blood test is to detect a recent myocardial. HDL, high density lipoprotein – this has the highest protein: lipid ratio, and so is the densest. It has the apoprotein A- 1. This is also called . High HDL levels are associated with lowered risk of cardiovascular disease. HDL levels are higher with exercise, higher estrogen levels, with alcohol consumption, and weight loss. The importance of lipoproteins. Lipoproteins show varying patterns that correlate with the risk of having a fatal cardiovascular event. High LDL, VLDL and triglyceride levels are associated with a high risk of atherosclerosis and heart disease. High HDL is correlated with reduced cholesterol levels, and a lower cardiovascular risk. Thus a high measurement of apo- A- 1 correlates with a low atherosclerosis risk. HDL levels drop with cigarette smoking, and rise with regular exercise, alcohol use, estrogen levels and weight loss. The lipid profile. An important part of the health evaluation is the lipid profile. This consists of measuring the total plasma cholesterol, the LDL, VLDL and HDL levels, as well as the triglyceride level. These numbers are studied together with other risk factors in your history, to decide whether treatment is required to bring down your cholesterol levels. High cholesterol does not produce any signs or symptoms, so a blood test is essential to evaluate the risk of atherosclerosis. All children should have one lipid profile between 9- 1. Adults without other risk factors should have a blood lipid profile once in 5 years at least. The effect of diet on the lipoprotein profile. A diet high in saturated fat is associated with a high cholesterol level. However, if it contains plenty of fish oils, which are rich in omega- 3 unsaturated fats, the cholesterol and triglyceride levels drop dramatically. Monounsaturated and polyunsaturated fatty acids, as in olive oil and peanut or sunflower oils, respectively, also reduce the blood cholesterol. References. Further Reading. The Ketogenic Diet and Cholesterol. A common misconception is that because ketogenic diets are high in fat, they must increase cholesterol in your body and clog your arteries. However, much of the recent research shines light on how low- carb diets can optimize your cholesterol levels and in fact improve your heart health. Here we show the most up- to- date research on how different types of cholesterol impact the body and how the ketogenic diet can be a useful tool in maintaining a robust cardiovascular system. Cutting through the Fat: What are Lipids and Cholesterol? Before we can examine the research, we need to understand the roles fat, cholesterol, and carrier molecules called lipoproteins play in the body. Fats, also known as lipids, are a diverse group of molecules with a “non- polar” characteristic that repels water. This means that you if you put a fat such as oil or grease in water they will not mix. In the human body, fats are most commonly found in the bloodstream in one of two forms. The first is triglycerides, a fatty acid that stores energy for later use. These long molecules can be broken down into other fatty acids and glycerol to create fuel for the body. Glycerol can further be broken down into forms of glucose. Elevated levels of triglycerides in your blood can increase your risk of developing diabetes, cardiovascular illnesses, and other life- threatening diseases. These molecules have a variety of functions in your body such as building hormones including estrogen and testosterone, maintaining the integrity of cell membranes, and aiding in the absorption of vitamins. Your body produces all the cholesterol you need through the liver and other body cells. Cholesterol is also obtained by consuming animal- based foods such as poultry, dairy, and red meat. Typically, 7. 5% of the body’s cholesterol is produced endogenously (internally) while the other 2. From least dense to most dense, they come in five forms: chylomicrons, very- low- density lipoproteins (VLDL), intermediate- density lipoproteins (IDL), low- density lipoproteins (LDL), and high- density lipoproteins (HDL). Because VLDL, LDL, and HDL cholesterol are frequently used as clinical indicators, we are going to focus on them. It is important to emphasize that while they are often referred to as “VLDL cholesterol”, “LDL cholesterol”, and “HDL cholesterol”, these molecules themselves are not cholesterol; they are cholesterol transporters. What is HDL Cholesterol? HDL cholesterol is frequently known as “the good cholesterol.” In addition to transporting cholesterol around the body, HDL collects cholesterol that is not being used by cells and brings them back to the liver to be recycled or destroyed. By doing this, HDL prevents cholesterol from accumulating and clogging arteries. Thus, elevated levels of cholesterol are integral in maintaining optimal cardiovascular health. Clinically acceptable levels of HDL cholesterol are 4. A recent research study published by De Nardo et al shows that HDL may be responsible in reducing inflammatory activity by regulating immune system cells called macrophages. However, there is general consensus among clinicians and scientists that HDL- cholesterol is healthy for the body and that higher levels of HDL- C are healthy for the body. For many years, physicians have used drugs called statins to increase HDL (and lower other forms of cholesterol). Recently, scientists have looked at utilizing dietary interventions as cost- effective methods to optimize HDL cholesterol and prevent the onset of cardiovascular diseases. Below we document three research studies examining low- carb and ketogenic diets effects’ on HDL. The Impact of Carbohydrate Restriction on HDL Cholesterol. In a recent meta- analysis published in the British Journal of Nutrition by Bueno et al, researchers investigated the impacts of very- low- carbohydrate ketogenic diets (VLCKD) on key metrics of cardiovascular health including HDL cholesterol. The authors defined a VLCKD as a diet lower in 5. They included 1. 3 randomized controlled studies with a total of 1,4. All studies took place for at least a full year and all subjects included were over 1. BMI of at least 2. In each of these studies, VLCKD diets were compared to low- fat diets. Overall, 1. 2 studies including 1. VLCKD on HDL cholesterol. When assessing the data, the individuals assigned to a VLCKD achieved an average increase in HDL of 0. L. This was double the average increase in HDL of the low- fat dieters who achieved an average increase in HDL of 0. L. The first group consumed a very- low- carbohydrate, high- saturated diet with 4%, 3. This equates to about 2. The second group consumed primarily a low- fat diet with 4. Both diets contained an equal number of calories. About 5. 9% of participants completed the 1. Both groups lost similar amount of body weight and body fat. The subjects who participated in the low- fat intervention experienced an average increase in HDL cholesterol of 0. L from 1. 3. 6 mmol/L to 1. L. Subjects who suffered from moderate to severe medical conditions such as diabetes, heart diseases, and active cancer were not included. Subjects of all different weights and BMIs were included as long as they were considered healthy. Scientists then randomly selected 6. HDL cholesterol. After adjusting for demographic factors such as age, sex, and ethnicity and lifestyle factors such as smoking, researchers noted that subjects in the lowest third of carbohydrate consumption had significantly higher levels of HDL cholesterol than subjects in the highest third of carbohydrate consumption. More specifically, subjects in the lowest third of carbohydrate consumption had an HDL concentration of 1. L while subjects in the highest third had HDL concentration of 1. L. You can accomplish this through a variety of low- carbohydrate diets, including the ketogenic diet. LDL Cholesterol: Clearing the Confusion. The story behind LDL, or low- density lipoprotein, is more complicated. LDL transports cholesterol produced by your liver and cells throughout your body. Unlike HDL, LDL molecules move slowly through the bloodstream and are vulnerable to oxidizing agents known as “free radicals.” Once oxidized, LDL can easily burrow itself into the walls of your arteries (called endothelium) and impede cardiovascular function. This triggers an inflammatory response in which white blood cells called macrophages rush to eat up the LDL. Typically known as the “bad cholesterol” to its healthy counterpart HDL cholesterol, increased levels of LDL cholesterol are associated with an increased risk of cardiovascular diseases (CVD). This is for two main reasons. First, LDL can be measured in two ways. The first is called LDL- C which measures the concentration of cholesterol transported by LDL in the blood. The second is called LDL- P which measures the number of LDL particles in the blood. Sometimes, there is a correlation – more LDL particles means that you can have higher levels of LDL- C. However, larger LDL molecules can grow and carry more cholesterol – leading to a discordance in which LDL- C and LDL- P are not necessarily proportional. When this happens, LDL- C and LDL- P are said to be “discordant.”For many years, LDL- C tests have been used as the primary method of measuring LDL in the blood. It is cheaper and easier to measure. Recent research has called into questioning how effective LDL- C is compared to LDL- P in precisely assessing cardiovascular risk. After reviewing cross- sectional data, a recent peer- reviewed paper from the world- renowned Framingham Heart Study stated that“In a large community- based sample, LDL- P was a more sensitive indicator of low CVD risk than either LDL- C or non- HDL- C, suggesting a potential clinical role for LDL- P as a goal of LDL management.” . That being said, LDL- C is still a useful indicator for future cardiovascular illness and ideally you want to have both low LDL- C and LDL- P. LDL can come in different forms – each with different effects on your health. A research study from 1. LDL is three times more likely to lead to heart disease than normal LDL . Additionally, more recent research shows that oxidation of LDL by substances called free radicals increases the risk of cardiovascular illness . Like LDL, VLDL transports cholesterol produced by the cells and liver throughout the body. However, VLDL particles also serve as the main transporters of triglycerides in the body. Additionally, they are composed of higher lipid and lower protein content than LDL. Because of their physical properties and functional purposes, VLDL particles are more likely than other lipoproteins to clog vessels and impair vascular functions. Research studies have noted that high levels of VLDL are associated with increased risk of artherosclerosis and cardiovascular diseases. In the meta- analysis by Bueno et al., low- carb diets were shown to increase HDL twice as much as low- fat diets after randomized controlled interventions. It also showed that there was a small increase in LDL- C in low- carb subjects compared to low- fat diet subjects who experienced no increase. The research study by Brinksworth et. The subjects’ ages ranged from 2. BMIs ranged from 2. Their intervention diets consisted of 1. Assuming a 2. 00. After the 1. 2 weeks intervention, researchers noted that the concentration of LDL particles decreased by 9. L 1. 18. 0 to 1. 06. L. Additionally, the particle size of LDL increased by an average of 5. However, they noted that the total number of VLDL particles decreased by 1. L to 6. 1. 7 nmol/L. In a randomized, parallel clinical trial, researchers recruited 1. The mean age of the subjects was 4. BMI was 3. 4. 4 kg/m. The second group of 6. After the intervention, researchers noted that the ketogenic diet group had decreased their VLDL by 7. VLDL by 6. 0%, and their small VLDL by 5. It is important to mention that LCKD did not lower total LDL cholesterol.
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November 2017
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