What is cholesterol?
Cholesterol is a four ringed, lipid molecule and is biosynthesized by all animal cells. It has the formula C27H46O.
Cholesterol enables animal cells to dispense with a cell wall to protect membrane integrity and cell viability, thus allowing them to change shape and move about (unlike bacteria and plant cells which are restricted by their cell walls). Cholesterol composes 30% of cell membranes. It makes the membrane more flexible and maintains the cell membrane. It means animals do not have to build cell walls as in plants or bacteria. It means animal cells can change shape readily which means animals can move.
Cholesterol is also important in intracellular transport, cell signaling and nerve conduction. The myelin sheath is rich in cholesterol and important for the conduction of nerves impulses.
All animal cells manufacture cholesterol, for both membrane structure and other uses, with relative production rates varying by cell type and organ function. About 20% of total daily cholesterol production occurs in the liver. Other sites of higher synthesis rates include the intestines, adrenal glands and reproductive organs.
The amount of cholesterol biosynthesized depends on the amount eaten. Eat more and you will make less. Eat less and your body will make more.
Cholesterol is present in bile and it aids the absorption of fats and fat soluble vitamins (Vit A, D, E, K).
A human male weighing 68 kg normally synthesizes about 1 g (1,000 mg) per day, and his body contains about 35g, mostly contained within the cell membranes. Cholesterol is essential for your body. It is both made internally (80%) and absorbed via food (20%). Cholesterol is also recycled in the body. The liver excretes it (via bile) into the digestive tract. Typically, about 50% of the excreted cholesterol is reabsorbed by the small bowel back into the bloodstream.
Ingested cholesterol has little effect on body cholesterol because (a) cholesterol in foods is poorly absorbed and (b) any changes in intake are compensated for by alternations in internal body production.
The body compensates for any absorption of additional cholesterol by reducing cholesterol synthesis. If Cholesterol is absorbed via food, for the first seven hours afterwards, the concentration of cholesterol in the blood increases. Seven to ten hours after ingestion there is little, if any effect on concentrations of cholesterol in the blood.
The fraction of cholesterol in the intestines which is absorbed varies from 15% to 75%, and averages about 50%, with the remainder excreted in the feces. However absorbed cholesterol is mostly cholesterol which was excreted by the liver into the bile, not from food. Recycled cholesterol.
Cholesterol is ubiquitous. All animal cells manufacture cholesterol and all animal meats and animal products (milk, cheese and eggs) contain cholesterol.
Okay Cholesterol is important. What foods is it in?
In your diet it is commonly in fat. That lamb cutlet with a layer of fat contains cholesterol. In the lamb fat you eat the main constituent is triglyceride. But the fat also contains other lipids such as cholesterol. Triglycerides are esters of three fatty acid chains and the alcohol glycerol. The three chains of fatty acids are each bonded to an OH group of the glycerol.
Eating plants prevents absorption of animal cholesterol. A little bit. Plants make cholesterol in very small amounts. Plants manufacture phytosterols (substances chemically similar to cholesterol produced within plants), which can compete with cholesterol for reabsorption in the intestinal tract, thus potentially reducing cholesterol reabsorption.
What is a fatty acid chain?
The major constituent of animal fat, triglycerides contain chains of fatty acids. A fatty acid is carboxylic acid attached to a long chain of C and H atoms. They are naturally occurring with an even number of C atoms from 4 to 28. The carbon atoms are linked into a zig-zag chain with hydrogen atoms to the side. The more carbon atoms there are in any fatty acid, the longer its chain will be, and so the longer ones melt at a higher temperature. The liver makes fatty acids for use by the rest of the body. There are many different types of fatty acids and they are essential to a healthy life.
In animal fat are lipids of various types. Fats are naturally occurring molecules that include fatty acids, oils, waxes, steroids, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, phospholipids, and cholesterol. So animal fat contains both fatty acids in triglycerides, fatty acids in phospholipids and cholesterol.
When we use the word fat to describe a food we are describing a mixture of triglyceride and phospholipids. Phospholipids are broken down in the healthy body to release their constituents, glycerol and fatty acids
Fat is an important foodstuff for many forms of life, and fats serve both structural and metabolic functions. Fats serve both as energy sources for the body, and as stores for energy in excess of what the body needs immediately. Animal fats are a complex mixture of triglycerides, phospholipids and other lipids. Triglycerides are the most common. Triglycerides contain three fatty acid chains and glycerol. Phospholipids contain two fatty acids and phosphate and glycerol. When we look at the lamb chop we are looking at fatty acids and glycerol. There will be very minimal bits of cholesterol
.
Many cell types can use either glucose or fatty acids for energy. Heart and skeletal muscle are good at using fatty acids. Glycerol from fats can be converted to glucose by the liver and become a source of energy.
What is the connection between cholesterol and fat?
Triglycerides (containing fatty acids), phospholipids and cholesterol are all lipids (insoluble in blood) and are transported around the body via lipoproteins.
Lipids (such as cholesterol) are not soluble in water or blood. In order to get around the body they are joined to proteins and then transported through the blood stream to the rest of the body. When lipids are joined to proteins they are called lipoproteins. In blood the main types are high-density lipoproteins or low-density lipoproteins. These are both made in the liver. HDL are normally considered good lipids. LDL are normally considered bad.
Lipoproteins. Why are they important?
Lipoproteins are special particles made of droplets of fats surrounded by a single layer of phospholipid molecules. Phospholipids are molecules which are attached to a phosphorus containing group. They have both a polar and a non-polar end. They carry molecules which are in-soluble in blood such as cholesterol.
Lipoproteins are the plasma lipoproteins (chylomicrons (ULDL), VLDL, IDL, LDL and HDL), the transmembrane proteins of the mitochondrion and the chloroplast and bacterial lipoproteins.
Is too much fat bad for you?
Fat is generally considered bad for you. Major epidemiological studies that look at large groups of people are interesting. ‘The China Study’ looked at Chinese people with a very poor traditional lifestyle. Their diet in China was very low in animal fat and dairy products and high in vegetables. Diet fat levels were half those of the USA. Their blood cholesterol was half that of the USA. They had virtually no heart disease, diabetes and cancer.
Initially the easy way to measure the amount of fat in your body was to measure cholesterol in the blood. There was a very good, cheap and reliable test for this. But nowadays the lipoproteins are seen as a better guide.
HDL is a lipoprotein that consists of a high proportion of protein and a little triglyceride and cholesterol. It transports cholesterol from the body to the liver and then via the gall bladder and the bile it is eliminated. HDL normally moves through the blood system, safely and without any collateral damage to the blood vessels.
LDL is a lipoprotein that consists of a moderate proportion of protein a little triglyceride and a high proportion of cholesterol. It carries cholesterol from the liver to the tissues of the body where it is stored. Each LDL particle carries approximately 1,500 molecules of cholesterol ester. In an unregulated environment the LDL molecules lead to atherosclerotic plaque formation. Atherosclerotic plaque is atheroma and means you are on the way to cardiovascular disease. For this reason LDL is called bad cholesterol.
The average LDL particle carries 3-6000 fat molecules some of which are cholesterol. The common view is that LDL particles are bad. HDL particles are good.
Fat in your diet
Fat in your diet normally consists of triglycerols. Which is chains of fatty acids joined to glycerol. Fat in your diet comes in many ways. Saturated fats, mono-unsaturated fats, polyunsaturated fats and trans fats.
In saturated fats the carbon atoms are only joined by single bonds not joined by double or triple bonds. There are no double bonds between the carbons in the chain. Saturated fats have the greatest possible number of hydrogen atoms. They are saturated with hydrogen. Therefore they find it difficult to react with other atoms or radicals. Saturated fats come from animal meats or animal products (milk, cheese) and palm oil and coconut oil. These have a higher melting point and are more likely to be solid at room temperature.
Unsaturated fats have one or more double bonded carbons in the carbon chain reducing the number of places where hydrogen atoms can bond to carbon atoms. They have a lower melting point and are more likely to be liquid at room temperature.
Mono means there is only one double bond. Mono-unsaturated fats come from olive oil and canola oil. Polyunsaturated means there are many double bonded carbon bonds.
If the third carbon from the end is a double bonded carbon then it is called an omega -3 fatty acid. Omega 3 fats are a type of polyunsaturated fat. They are general considered good. They decrease inflammation and are good for disease such as dementia and arthritis. Omega 3 fats come in fish oil and flax seed.
Omega 6 fat is another type of polyunsaturated fat. Omega 6 fats come from vegetable oils and nuts. Can also come from meat (animal and fish). They often react with oxygen in the air and go rancid. (Olive oil, sunflower oil) Can be neutral or protective.
Trans fats occur when you artificially heat an oil and deep fry food in it. Trans fats are normally considered the worse type of fat. They are man-made. Do not occur naturally.
How do you decrease your cholesterol level?
Your cholesterol level is a guide to your lipoproteins which are a guide to the status of your arteries (especially the coronary ones). Your cholesterol level is important and should be known.
Nowadays bad cholesterol levels are treated by strict dieting (low saturated fat, trans fat-free, low cholesterol foods,) and medications such as statins. Studies have shown that statins work. They decrease bad cholesterols in the blood and decrease heart problems.
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