● 美食 與 膽固醇的關係 -

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膽固醇 (Cholesterol)
      膽固醇 (別名膽甾醇)是一種類固醇及甾醇，化學式為C27H46O。固態之下是一種無色的結晶。膽固醇廣泛存在於動物體的細胞膜中，同時也是合成幾種重要荷爾蒙及膽酸的材料。膽固醇可以分成兩種，低密度脂蛋白膽固醇(LDL-C)及高密度脂蛋白膽固醇(HDL-C)。若血液中膽固醇的總含量過高，則發生心血管疾病的機率會提高。
     膽固醇是在1784年在膽石首次被發現的。其命名為希臘文中的chole- (膽汁)加上stereos (固體)，再加上其化學結構中有羥基，故再接上"-ol"在結尾上。膽固醇在人體內扮演著重要角色，可說是一種與生命現象息息相關的重要化合物。
膽固醇與健康
      膽固醇過高或過低都會造成健康風險；總膽固醇最佳值是在160mg/dl~200mg/dL之間，此時擁有最低的健康風險；低於130mg/dL就需要檢查是否有重病或營養不良、也會增加出血性中風、憂鬱等疾病風險，超過240mg/dL也是不健康到需要治療。
      吃下肚的酯質進入十二指腸後，會由叫做胰脂酶的酵素部分分解，釋出其中的脂肪酸，由肝臟合成成為膽固醇。
      膽固醇通常能在肝臟與細胞來去，並在必須時經由肝臟轉換成脂蛋白供人體使用；膽固醇不溶於水，與低密度脂蛋白及高密度脂蛋白結合，隨血液運行。如果低密度脂蛋白比高密度脂蛋白多出太多，在血液中運行的膽固醇就會多於細胞所需的量，這時過剩的膽固醇會積聚在血管壁上。這個過程叫做動脈粥樣硬化，會導致心臟病。但當膽固醇凝結在血管壁上將阻礙血流，嚴重時形成血栓，可能併發心血管疾病，如高血壓、中風。
      膽固醇若過低，則容易造成出血型中風、憂鬱等疾病；不然就是癌症等重病造成的；不過多數健康人不用擔心飲食會造成此風險，只有純素者會有因為飲食而造成膽固醇過低的風險，飲食中只要有少量的雞蛋、牛奶、魚肉或其他動物性食品，大多不會造成膽固醇過低。

You need to know about Cholesterol
1. Cholesterol is “just” another fancy organic molecule in our body but with an interesting distinction: we eat it, we make it, we store it, and we excrete it – all in different amounts.
2. The pool of cholesterol in our body is essential for life. No cholesterol = no life.
3. Cholesterol exists in 2 forms – unesterified or “free” (UC) and esterified (CE) – and the form determines if we can absorb it or not, or store it or not (among other things).
4. Much of the cholesterol we eat is in the form of CE. It is not absorbed and is excreted by our gut (i.e., leaves our body in stool). The reason this occurs is that CE not only has to be de-esterified, but it competes for absorption with the vastly larger amounts of UC supplied by the biliary route.
5. Re-absorption of the cholesterol we synthesize in our body (i.e., endogenous produced cholesterol) is the dominant source of the cholesterol in our body. That is, most of the cholesterol in our body was made by our body.
6. The process of regulating cholesterol is very complex and multifaceted with multiple layers of control. I’ve only touched on the absorption side, but the synthesis side is also complex and highly regulated. You will discover that synthesis and absorption are very interrelated.
7. Eating cholesterol has very little impact on the cholesterol levels in your body. This is a fact, not my opinion. Anyone who tells you different is, at best, ignorant of this topic. At worst, they are a deliberate charlatan. Years ago the Canadian Guidelines removed the limitation of dietary cholesterol. The rest of the world, especially the United States, needs to catch up. (Peter Attia, M.D.)
http://eatingacademy.com/nutrition/the-straight-dope-on-cholesterol-part-ii

膽固醇在人體內移送過程 Cholesterol trafficking

Cholesterol and Risk Factors
There are numerous risk factors for cholesterol. Some of these are directly linked to diet, whereas others could have links to genetics, general lifestyle or illnesses. Varying risk factors include:
● Gender — statistics show that men are at an increased risk of developing the condition. Although women have a lower risk factor due to the protective effects of the hormone oestrogen, early menopause can increase the risk in some cases.
● A sedentary lifestyle with not enough or minimal exercise can cause high levels of cholesterol. This is most common in people with a desk job or full-time drivers who are unlikely to get a large amount of exercise.
● Smoking can cause unnecessary blockage in your artieries and increases your risk of developing high levels of cholesterol.
● Being overweight and/or obese will mean you are more prone to suffering from high levels of cholesterol.
● An unhealthy diet with too much salt or sugar (or both) can also affect levels.
● Other chronic illnesses such as diabetes, high blood pressure or kidney disease.

Cholesterol plaques accumulate at the inside lining of blood vessel. Eventually, they result in the blockage of blood vessel.