What is cholesterol, HDL and LDL?
Cholesterol is a waxy substance with a molecular weight of about 387g/mol. It is an essential part of the cell membranes of all animals. It is needed to ensure the correct pliability and permeability of the cell membranes. It is also a necessary building block for many hormones like sex hormones and corticosteroids, of several fat-soluble vitamins, and of the bile acids.
Since Cholesterol is not water-soluble, it cannot be just dissolved in the bloodstream for transportation. Cholesterol is therefore bound to large complexes of proteins, fats and other lipids to form large complexes for transportation. The two main kinds of transport complexes are called low-density-lipoprotein (LDL) and high-density-lipoprotein (HDL).
HDL has the highest protein content and is therefore denser than other lipoprotein-complexes. HDL is also known as “good cholesterol”, as levels over 60mg/dl in the blood are associated with protection from atherosclerosis and heart disease. Levels below 40mg/dl in men and 50 mg/dl in women signal an increased risk for heart disease, myocardial infarctions and stroke. Scientists believe that HDL can remove cholesterol from atherosclerotic plaques (“reverse cholesterol transport”), and transports it to the liver and to the adrenal gland and gonads. This is how researchers believe it confers protection from heart disease.
LDL is the so-called bad cholesterol which is associated with a higher risk for heart disease, atherosclerosis, myocardial infarctions and stroke. It consists of a single Apo-B and a single B-100 protein chain and has a core of fatty acids and about 1500 cholesterol molecules. Everything is covered by a layer of more cholesterol molecules and phospholipids. LDL is the main transporter of cholesterol from the liver to other cells in the body. However, LDL can invade the endothelium (the inner lining of the blood vessels) where it can become oxidized. Oxidized LDL particles can stick to certain molecules called proteoglycans in the wall of arteries and thus start the formation of atherosclerotic plaques. Therefore increased levels of LDL in the blood stream are associated with atherosclerosis, heart attack, and stroke.
What are free fatty acids, and triglycerides?
Fats as they are found in our diet consist of three fatty acids that are bound via ester-bond to a glycerol molecule. This is the reason why regular fats are also called triglycerides. Compounds consisting of two fatty acids, bound to a glycerol molecule that also has a hydrophobic end, are called lipoids, and they are vital components of our cell membranes. Our body can clip the ester-bond between the glycerol-molecule and the fatty acids easily. The result consists of free fatty acids and a glycerol molecule that can be further metabolized.
Foods that will Lower Your Cholesterol
The most obvious way to lower cholesterol level in the blood seems to be very easy: Stay away from food high in cholesterol. High cholesterol levels are found in all animal tissues, with highest amount in fatty tissues. Lean meat and fish does contain cholesterol, but to a much lower degree than fat meat. Egg yolks, and high-fat diary products like cheese, whipping cream and ice cream are also a rich source of cholesterol. Staying away from these types of food will ensure that my cholesterol level is low, right? Well, yes, maybe, if you’re lucky….
Dietary cholesterol is not the only source of the cholesterol in our blood stream. Our own liver is busily synthesizing it, too. How busily, is mainly determined by genetics, so if you have a family history of high cholesterol levels, you most likely need to do more than staying away from high-cholesterol food to keep you own levels in check. This is where the other pathways our body uses to control cholesterol levels, come into place.
Niacin (aka Vitamin B3) can inhibit cholesterol synthesis in the liver. The body reacts with increasing the amount of LDL-receptors on its cells which increases the clearing of LDL from the blood stream. It also increases cholesterol recycling which might increase HDL levels. Niacin is found in foods like lean beef, chicken, tuna, and salmon, and also in plant derived foods like avocados, dates, tomatoes, leafy vegetables, broccoli, carrots, sweet potatoes, asparagus, nuts, whole grain products, legumes, mushrooms, and brewer's yeast.
A few members of the Vitamin E family (tocotrienols) can also inhibit cholesterol synthesis by the liver. Many of the plant derived foods that contain high levels of Niacin also contain high levels of Vitamin E like e.g. avocados, leafy vegetables, broccoli, asparagus, nuts, whole grain products, legumes, mushrooms, and brewer's yeast.
The relative amount of carbohydrate and proteins in ones’ diet can also influence cholesterol levels, as insulin which is secreted in response to carbohydrates increases cholesterol synthesis in the liver. Insulin has a hormone complement that has the opposite action: while insulin lowers blood sugar by inducing sugar consumption in muscle cells and sugar storage in the liver or by converting it to fat in fat tissue, glucagon, insulin’s complement, increases blood sugar levels by mobilizing sugar from the liver. As the true opponent of insulin, glucagon also inhibits cholesterol synthesis. Since diets high in protein and low in carbohydrate decrease insulin secretion and increase glucagon secretion, these diets can lower blood cholesterol levels. These diets do not increase blood sugar levels by increasing glucagon secretion, as it is rather the other way around. These diets decrease blood sugar levels, and the body reacts with increasing glucagon synthesis to provide enough blood sugar which is the main fuel for many tissues, for the body to function properly.
Eating low amounts of saturated fats lowers blood levels of triglycerides. This in turn can lower LDL levels, as triglycerides are needed in the formation of LDL-particles.
Fructose can increase the production of LDL-particles, as it increases the production of a preliminary stage of them. Foods to avoid are therefore processed foods that contain high-fructose corn-syrup and large amounts of sucrose (regular sugar).
LDL-particles need to be oxidized before they can stick to the artery walls and form atherosclerotic plaques. While scientific evidence is inconsistent on whether eating foods rich in anti-oxidants like blueberries, pomegranates, and other fresh brightly colored fruits and vegetables can help, these foods might reduce the harmful effects of high LDL levels in the blood by preventing the LDL from getting oxidized.