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\'Good\' or \'Bad\' Cholesterol?

(2007-10-04 08:11:50) 下一个

1. Some Basics Before We Start:

Cholesterol is a sterol (a combination steroid and alcohol), a lipid found in the cell membranes of all body tissues. The name originates from the Greek chole- (bile) and stereos (solid), and the chemical suffix -ol for an alcohol. Most of your body’s cholesterol (75%) is synthesized by the body and some has dietary origin (25%).

Cholesterol is more abundant in tissues which either synthesize more or have more abundant densely-packed membranes, for example, the liver, spinal cord, brain, and atheromata (arterial plaques).

Cholesterol is insoluble in blood, but is transported in the circulatory system bound to one of the varieties of lipoprotein, spherical particles which have an exterior composed mainly of water-soluble proteins. The term "bad cholesterol" has been used to refer to cholesterol carried by LDL (low-density lipoprotein) which, according to the lipid hypothesis, is thought to have harmful actions. The term "good cholesterol" to refer to cholesterol contained in HDL (high-density lipoprotein), thought to have beneficial actions. So, good cholesterol's technical name is high density lipoprotein or HDL cholesterol. Second, cholesterol in itself is neither good nor bad, it depends on which type carrier the cholesterol happens to be.

With HDL cholesterol, this cholesterol is being taken away from the heart and arteries to the liver where the cholesterol is broken down and excreted from the body. Ideally, you should try to raise your good cholesterol level if you want to have a healthy heart. A high HDL cholesterol level is considered to be 60 mg/dl or above. If you can reach this level of 60 mg/dl or above, researchers believe you can offset other causes that put you at risk for heart disease. While 60 mg/dl is a good level to aim for, you should have at least 30 mg/dl or above if you are a woman or 40 mg/dl or above if you are a man.

2. Functions of Cholesterol in your body:

Cholesterol is required to build and maintain cell membranes; it regulates membrane fluidity over a wider range of temperatures. Hibernators have a higher percentage of cholesterol in their cell membrane so their cell membrane remains fluid-like to sustaine a normal function. The hydroxyl group on cholesterol interacts with the phosphate head of the membrane, while the bulky steroid and the hydrocarbon chain is embedded in the membrane. Some research indicates that cholesterol may act as an antioxidant.[2] Cholesterol also aids in the manufacture of bile (which is stored in the gallbladder and helps digest fats), and is also important for the metabolism of fat soluble vitamins, including vitamins A, D, E and K. It is the major precursor for the synthesis of vitamin D and of the various steroid hormones (which include cortisol and aldosterone in the adrenal glands, and the sex hormones progesterone, the various estrogens, testosterone, and derivatives).

Most notably, cholesterol is an essential part of the myelin sheath (that is why you do not want to cut cholesterol intake to a child whose central nerves system is rapidly developing, this is how we started on this topic). The myelin sheath, similar to the coating on our house copper wire, ensures that the brain functions properly by aiding the passage of electrical impulses. Without the myelin sheath, it is difficult to focus and we can lose memory (too many "electrical" sparks among nerve fibers short-cutting signal transduction). Recently, cholesterol has also been implicated in cell signalling processes, where it has been suggested that it forms lipid rafts in the plasma membrane. It also reduces the permeability of the plasma membrane to hydrogen ions (protons) and sodium ions.[3]

3. Cholesterol Synthesis and intake:

Cholesterol is required in the membrane of mammalian cells for normal cellular function, and is either synthesized in the endoplasmic reticulum, or derived from the diet, in which case it is delivered by the bloodstream in low-density lipoproteins. These are taken into the cell by receptor-mediated endocytosis in clathrin-coated pits, and then hydrolysed in lysosomes.

       1) Synthesis: The HMG-CoA reductase pathway ------- too technical, you may skip to the intake section.

Cholesterol is primarily synthesized from acetyl CoA through the HMG-CoA reductase pathway in many cells and tissues. About 20 – 25% of total daily production (~1 g/day) occurs in the liver; other sites of higher synthesis rates include the intestines, adrenal glands and reproductive organs. For a person of about 150 pounds (68 kg), typical total body content is about 35 g, typical daily internal production is about 1 g and typical daily dietary intake is 200 to 300 mg in the United States and societies adopting its dietary patterns. Of the cholesterol input to the intestines via bile production, 92-97% is reabsorbed in the intestines and recycled via enterohepatic circulation.

Konrad Bloch and Feodor Lynen shared the Nobel Prize in Physiology or Medicine in 1964 for their discoveries concerning the mechanism and regulation of the cholesterol and fatty acid metabolism.

Cholesterol is minimally or not soluble in water/blood plasma; it cannot dissolve and travel in the water-based bloodstream. Instead, it is transported in the bloodstream by lipoproteins - protein "molecular-suitcases" that are water-soluble and carry cholesterol and triglycerides internally. The apolipoproteins forming the surface of the given lipoprotein particle determine from what cells cholesterol will be removed and to where it will be supplied. The largest lipoproteins, which primarily transport fats from the intestinal mucosa to the liver, are called chylomicrons. They carry mostly fats in the form of triglycerides and cholesterol. In the liver, chylomicron particles release triglycerides and some cholesterol. The liver converts unburned food metabolites into very low density lipoproteins (VLDL) and secretes them into plasma where they are converted to low-density lipoprotein (LDL) particles and non-esterified fatty acids, which can affect other body cells.

In healthy individuals, the relatively few LDL particles are large. In contrast, large numbers of small dense LDL (sdLDL) particles are strongly associated with the presence of atheromatous disease within the arteries. For this reason, LDL is referred to as "bad cholesterol".

The 1987 report of National Cholesterol Education Program, Adult Treatment Panels suggest the total blood cholesterol level should be: <200 mg/dl normal blood cholesterol, 200-239 mg/dl borderline-high, >240 mg/dl high cholesterol.<

High-density lipoprotein (HDL) particles transport cholesterol back to the liver for excretion, but vary considerably in their effectiveness for doing this. Having large numbers of large HDL particles correlates with better health outcomes, and hence it is commonly called "good cholesterol". In contrast, having small amounts of large HDL particles is independently associated with atheromatous disease progression within the arteries.

     2) Dietary Intakes: 

Cholesterol is found in animal fats: all food containing animal fats contains cholesterol; food not containing animal fats either contains no cholesterol or negligible amounts. Major dietary sources of cholesterol include eggs, beef and poultry.<

Plants have trace amounts of cholesterol, so even a vegan diet, which includes no animal foods, has traces of cholesterol. However, the amounts are very small. For example, to ingest the amount of cholesterol in one egg, one would need to drink about 9.6 litres (19.57 pounds) of pure peanut oil !!!!!!!!!

Plant products (e.g. flax seed, peanut), also contain cholesterol-like compounds, phytosterols, which are suggested to help lower serum cholesterol. While both saturated and trans fats increase levels of LDL cholesterol (so-called "bad" cholesterol), trans fats also lower the levels of HDL cholesterol (so-called "good" cholesterol) [2]; this increases the risk of coronary heart disease (CHD). The NAS is concerned "that dietary trans fatty acids are more deleterious with respect to CHD than saturated fatty acids". Trans fats are harmful because they are absorbed by the body's cell membranes as if they were cis fats, causing the cells to become partially hydrogenated, which disrupts cell metabolism.

Vegetarians have been shown to have a 24% reduced risk of dying of heart disease. The most powerful cholesterol-lowering agents are soluble fiber, unsaturated fats, and phytochemicals, all of which are found almost exclusively in plant foods.

In the seventeen studies conducted between 1978 and 2002, the average vegan’s cholesterol level was 160 mg/dl, while the average non-vegetarian’s cholesterol was 202 mg/dl

4. Diet that can help to lower body Cholesterol, including the famed Cretan Mediterranean-style diet:

The Seven Country Study found that Cretan men had exceptionally low death rates from heart disease, despite moderate to high intake of fat. The Cretan diet is similar to other traditional Mediterranean diets: consisting mostly of olive oil, bread, abundant fruit and vegetables, a moderate amount of wine, and fat-rich animal products such as lamb, sausage and goat cheese. However, the Cretan diet consisted of less fish and wine consumption than some other Mediterranean-style diets, such as the diet in Corfu, another region of Greece, which had higher death rates.

The Lyon Heart Study set out to mimic the Cretan diet, but adopted a pragmatic approach. Realizing that some of the people in the study would be reluctant to move from butter to olive oil, they used a margarine based on rapeseed (canola) oil. The dietary change also included 20% increases in vitamin C rich fruit and bread and decreases in processed and red meat. On this diet, mortality from all causes was reduced by 70%. This study was so successful that the ethics committee decided to stop the study prematurely so that the results of the study could be made available to the public immediately.

5. Here are some principles or tips to make a low cholesterol diet successful:

1). Load on lots of fruits and vegetables because these are low in calories, cholesterol, and fat
2). Lower your intake of saturated fats or the foods that contain these to lower the possibility of developing heart diseases
3). Take note of "trans-fatty" elements that are usually found in partially hydrogenated vegetable oils like margarines and shortenings because they increases blood cholesterol levels the way saturated fat does
4). Consume foods that use whole grain foods instead of those that contain white flour
5). Compared regular, full-fat dairy products, opt for low fat or skimmed ones. These are not only good for your cholesterol level but also for your weight as well
6). Choose lean meats like turkey and chicken meats instead of red meat because it is closely-associated with decreasing cholesterol levels
7). Use olive and canola oils when cooking instead of using cooking oils because these are higher in monounsaturated fats that help lower cholesterol levels
8). Plant products (e.g. flax seed, peanut), also contain cholesterol-like compounds, phytosterols, which are suggested to help lower serum cholesterol. Cosco/PriceClub has the flax seed which also bumps up your daily omiga-3 fatty acid.

6. Some foods that can help to lower body Cholesterol:

Just recap of what have been said earlier:

The word “cholesterol” can refer either to the cholesterol found in the body (blood cholesterol) OR the cholesterol found in food (dietary cholesterol). You get cholesterol in two ways. Your liver makes about 75% cholesterol for your body and the rest about 25% comes from animal products that you eat, such as meats, eggs, and dairy products. Some foods contain saturated or trans-fats, which also cause/increase your body to make cholesterol. The foods that raise your blood cholesterol the most are saturated fat and Trans fat in such foods as fatty meat and whole-fat dairy products, snack foods and ready-prepared foods.

Foods that have high levels of dietary cholesterol include egg yolks, organ meats, shrimp, squid and fatty meats. In terms of food or dietary cholesterol, there is no “good” or “bad” cholesterol at all !!! Dietary cholesterol is absorbed just like other food particles into the blood stream to maintain your bosy’s function. It is when they are bound to LDL or HDL their functions differ from there on, either "good" or "bad". SO when you hear people saying things like (鸡蛋黄里的胆固醇是好胆固醇,人体需要;鱿鱼里的胆固醇是坏胆固醇,要避免摄入), just give them a witty smile, and if worth it, educate them.

According to the American Heart Association, "You can reduce cholesterol in your blood by eating healthful foods, losing weight if you need to and exercising." What follows is a listing of the most potent foods to add to your diet if you want to fight high cholesterol and drive your levels down using your diet as a primary tool

1). Shitake Mushrooms. The active component in shitake mushrooms--eritadenine--has been found to lower cholesterol levels in animal studies. The more eritadenine the animals received, the more their cholesterol levels dropped
2). Walnuts. A study in the April 2004 issue of Circulation found that when walnuts were substituted for about one-third of the calories supplied by olives and other monounsaturated fats in the Mediterranean diet, total cholesterol and LDL (bad) cholesterol were reduced. Walnuts contain the beneficial omega-3 fatty acids, which are known to be excellent for the heart
3). Soy. A new study found that eating two servings of soy protein a day can lower cholesterol by up to 9 percent--but it must not be overcooked to have benefit. "Soy protein increases the activity of low-density lipoprotein receptors primarily on the liver that clears it from the body. Eating soy protein increases the activity of these enzymes that break down the cholesterol," said study author James Anderson, a scientist at the University of Kentucky in Lexington. Good soy sources would be edamame or soy nuts. "Soy-fortified muffins, cereals or nutritional bars in which the soy protein was baked at high temperatures do not provide the benefit,"
4). Blueberries. Researchers with the U.S. Department of Agriculture have identified an antioxidant in blueberries called pterostilbene (it's similar to resveratrol, the antioxidant found in grapes and red wine). This compound has effectively lowered cholesterol levels in animal studies.
5). Salmon. This fish is a particularly good source of omega-3 fatty acids, which are known to lower LDL cholesterol while raising the good (HDL) kind.
6). Garlic. Numerous studies have demonstrated that eating garlic regularly reduces LDL cholesterol and raises HDL levels.
7). Avocado. Avocados are rich in oleic acid, a monounsaturated fat known to help lower cholesterol. In fact, one study found that people with moderately high cholesterol levels who ate a diet high in avocados for one week had significant drops in total and LDL cholesterol levels, and an 11 percent increase in the good HDL cholesterol.
8). Black Beans. Black beans and other legumes are high in dietary fiber, which is an excellent cholesterol fighter.
9). Apples. Rich in both pectin and fiber, along with powerful antioxidants, including quercetin, catechin, phloridzin and chlorogenic acid, apples help lower bad cholesterol while raising the good kind
10). Dark Green, Leafy Vegetables. According to the National Heart, Lung and Blood Institute's Family Heart Study, participants who ate four or more servings of fruits and vegetables a day had significantly lower levels of LDL cholesterol than those who ate fewer servings. Among the most powerful veggies are the dark green, leafy variety, such as spinach, kale, collard greens and Swiss chard.
11). Olive oil or other veggi oils that contains primarily mono- or poly-unsaturated faty acids. As discussed earlier, they will increase the HDL level, decrease the LDL level, and off-set the detrimental effects of dietary animal fat and dietary cholesterol.

            If anyone needs references regarding this, please let me know QQH.

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闲人忙人 回复 悄悄话 嘻嘻!现在可以写了。多谢!
MDGG 回复 悄悄话 闲人忙人: sure thing. I'll try my best if I could answer any questions.