Fats and oil (3)
This is a wax-like substance that is produced in the liver and is also found in certain foods that we eat. Cholesterol has for long been given a bad name, as though we as human beings can and should do without it. In my research and writing of this article, I have come to the conclusion that cholesterol is not bad as many have tried to show in the past. Hopefully, this will become clear to us as we continue in this article.
First of all, we shall look at the functions of cholesterol and in doing so, determine the actual status of cholesterol in the body.
Functions of cholesterol: Cholesterol is required to build the cell membrane and in human and animal cells, it maintains the integrity and rigidity of the cell.
Cholesterol is involved in reducing the permeability of the plasma membrane to hydrogen and sodium ions and to solutes like water. The function of cholesterol is particularly important in conditions of dehydration and when the body has to go into a redistribution mode. This is a condition whereby water has to be re channeled from the muscles, joints and bones to the five vital organs (brain, heart, liver, kidneys and the lungs).
In a state of dehydration, the brain sends signals to the liver to produce more cholesterol, which will act as adhesive plugs between cells instead of water. With cholesterol forming the adhesive plugs, the rate of permeability of water becomes drastically reduced and excess water in the circulation is made available to the vital organs.
In the liver, cholesterol is a precursor molecule for various biochemical reactions.
Cholesterol is used for the synthesis of bile. Bile is either stored in the gall bladder or it is passed into the small intestine to assist in the absorption of fats and the fat-soluble vitamins; A, D, E and K. In the small intestine, bile is converted into bile salts which enhance the solubility of fats. It therefore, helps in the absorption of fats and the vitamins that are soluble in fats.
Cholesterol is also a precursor for the synthesis of vitamin D, the steroid hormones and the sex hormones (progesterone, oestrogen and testosterone). The adrenal hormones, cortisol and aldosterone are also synthesized from cholesterol.
Looking at all these functions of cholesterol, it becomes easy to determine if cholesterol is good or not. The problems that would occur in a state of cholesterol deficiency are numerous. We shall be looking at these in the concluding part of this article next week.
Sources of dietary cholesterol: As I have already mentioned, cholesterol is synthesized in the liver. This accounts for 20 to 30 per cent of the daily production of cholesterol in the body. Cholesterol is further synthesized in other cells of the body.
Apart from these endogenous sources of cholesterol, there are exogenous sources of cholesterol. The main exogenous sources of cholesterol are from the animal kingdom and these include beef, pork, chicken and turkey skin, fish, shrimp, egg yolk and cheese. Cholesterol is not found in plants, but there is a phytochemical, similar to cholesterol, known as phytosterol that is produced in some plants.
Phytosterol: Phytosterols are cholesterol-like compounds found in such plants as avovado, peanuts and flaxseed. They do not function as cholesterol, instead, they compete with it for the same receptor site and also reduce the absorption of both dietary and bile cholesterol. In this role, they directly reduce LDL-cholesterol.
LDL and HDL – cholesterol: Cholesterol, being only slightly soluble in water, dissolves to a very small concentration in blood, which is predominantly water-based. To increase the concentration of cholesterol in the blood and the tissues where they are to be carried to, they are transported in lipoproteins. Lipoproteins are lipid (fat) and protein complexes that move around the blood carrying cholesterol. There are different kinds of lipoproteins in the blood stream, but two are of interest to us in this article.
Depending on the density, we have the Low-Density Lipoprotein, otherwise known as LDL-Cholesterol and secondly is the High-Density Lipoprotein, HDL-cholesterol. LDL particles are the main transporters of cholesterol in the blood stream. They transport cholesterol from the liver to the cells where they are used, while HDL transports cholesterol from the cells to the liver to be excreted or to other tissues where they are used for hormone synthesis.