How the body protects us from potentially toxic amounts of sugar
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一.Science News:How the body protects us from potentially toxic amounts of sugar
Too much sugar can cause liver damage and raise the risk for other medical problems. Now, researchers studying mice have learned that the small intestine protects the liver from exposure to one type of sugar, called fructose. But the small intestine has its limits, the study finds. High doses of fructose overwhelm the intestine’s ability to process the sugar. Researchers reported those results February 6 in Cell Metabolism.
Fructose is a type of simple sugar. It’s found in honey and fruits, as well as in table sugar and in many sweetened foods and drinks. To use fructose for energy, the body needs to convert it into another type of simple sugar, called glucose, or into other smaller molecules. But too much fructose puts a strain on the body. For example, in people it puts the liver at risk for conditions such as fatty liver disease. It also raises the risk of obesity and type 2 diabetes (DIE-uh-BEAT-eez).
Scientists knew fructose could be broken down and absorbed in both the liver and the small intestine. But they believed the liver was mainly responsible for the process. The new study suggests otherwise. It finds that moderate doses of fructose are transformed in the small intestine. The liver steps in only when the dose of fructose is too high for the small intestine to handle.
In that way, the small intestine shields the liver from dangerously high doses of fructose, says Joshua Rabinowitz. One of the study authors, he works at Princeton University in New Jersey. He studies how the body breaks down chemicals.
But how much fructose is too much is still up in the air. Rabinowitz and colleagues fed mice a sugar mix that contained equal parts glucose and fructose. (That’s the ratio in basic table sugar.) Some mice got a lower dose of sugar, and some got a higher dose.
The researchers used a special technique to chemically “label” the sugar molecules they gave to the mice. The method involved swapping certain carbon atoms out for a slightly heavier form of carbon. That allowed the researchers to track which sugars were being transformed and where their by-products were ending up.
Later, the researchers collected samples from different mouse organs. Then they separated out the sugar by-products by weight and identified the molecules with heavier carbon.
At lower sugar doses, researchers found lots of by-products from labeled fructose molecules in the small intestine. But they found only small amounts in the liver. The same was true in the vein that connects the small intestine to the liver. Lots of glucose molecules were found in this vein, though. The chemical labels showed some had been transformed from fructose molecules in the small intestine.
At high sugar doses, the small intestine couldn’t keep up. The vein connecting the intestine and liver had a much higher ratio of fructose to glucose than at lower sugar doses. That suggests the small intestine was passing some fructose along to the liver.
Translating these findings into dietary recommendations for people could be challenging because mice burn more energy relative to their body weight than people do, cautions Luc Tappy. He’s a physiologist at the University of Lausanne in Switzerland. He wasn’t part of the study. He notes that it’s hard to compare sugar doses between humans and mice.
Plus, Rabinowitz adds, scientists don’t know whether the small intestine is a safer place than the liver to process fructose. His lab plans to research that next.
二.重點摘譯
太多的糖會造成肝臟損傷，並增加其他醫療問題的風險。現在，研究小鼠的研究人員已經了解到，小腸可以防止肝臟接觸一種稱為果糖的醣類。研究發現，小腸有其局限性。高劑量的果糖壓倒了腸子處理糖的能力。研究人員在2月6日的Cell Metabolism中報導了這些結果。
果糖是一種簡單的糖。它出現在蜂蜜和水果，以及餐桌糖和許多甜食和飲料中。為了使用果糖能量，身體需要將其轉化為另一種簡單的糖，稱為葡萄糖或其他小分子。但過多的果糖會對身體造成壓力。例如，在人們中，肝臟處於諸如脂肪肝疾病的風險之中。它也增加了肥胖和2型糖尿病的風險（DIE-uh-BEAT-eez）。
科學家知道果糖可以分解並吸收到肝臟和小腸中。但他們認為肝臟主要負責這一過程。新研究表明否則。它發現中等劑量的果糖在小腸中轉化。只有當果糖的劑量太高而不能處理小腸時，肝臟才會進入。
就這樣，小腸將危險的高劑量果糖屏蔽肝臟。作者之一的Joshua Rabinowitz說，他在新澤西州普林斯頓大學工作。他研究人體如何分解化學物質。
但是果糖多少還在空氣中。 Rabinowitz和同事給小鼠餵食含有等量葡萄糖和果糖的糖混合物。 （這就是基本食糖的比例）。一些老鼠的糖分含量較低，有些則得到了較高的劑量。
研究人員用一種特殊的技術來化學“標記”他們給小鼠的糖分子。該方法涉及將某些碳原子換成較輕的較重形式的碳。這使得研究人員能夠跟踪哪些糖正在轉化以及其副產物在哪裡結束。
後來，研究人員收集了來自不同老鼠器官的樣本。然後他們按重量分離出糖副產物並用較重的碳鑑定出這些分子。
在較低的糖劑量下，研究人員在小腸中發現了大量來自標記的果糖分子的副產物。但他們在肝臟中只發現少量。連接小腸和肝臟的靜脈也是如此。儘管如此，還是發現了許多葡萄糖分子。化學標籤顯示一些已經從小腸中的果糖分子轉化而來。
在高糖劑量下，小腸無法跟上。連接腸道和肝臟的靜脈的果糖與葡萄糖的比例要比較低的糖劑量高得多。這表明小腸會通過一些果糖到肝臟。
Luc Tappy警告說，將這些發現轉化為對人們的飲食建議可能是具有挑戰性的，因為老鼠相對於他們的體重燃燒更多的能量。他是瑞士洛桑大學的生理學家。他不是這項研究的一部分。他指出，很難比較人和小鼠之間的糖劑量。
此外，Rabinowitz補充說，科學家們不知道小腸是否比肝臟更安全，以處理果糖。他的實驗室計劃下一步研究。
三.延伸閱讀
吃糖可以很好的補充能量。我們有很多的運動員在參加劇烈的運動之前，往往是不能吃過於撐肚子的食物，但是又不得不補充能量，所以會選擇糖來補充能量，因為糖只需要點點就可以釋放很多的能量。是高能量的食物。
其次，可以提高血壓。很多人都患有低血壓，在感覺頭暈炫目的時候不知道咋辦，可以告訴你，糖是提高血壓的最好的物質之一，所以當感覺血壓過低的時候，可以適量的吃些糖類食物。
最後，糖可以減輕一個人的壓力。很多時候人感覺有壓力的時候都會選擇嘴裡含著糖，因為這樣的話可以給自己一個心理提示，嘴是甜的，生活還會苦嗎？所以很多運動員在參加一些重要的比賽的時候都會選擇口裡嚼著口香糖。
四.心得
果糖在生活中是很常見的，從文章中可以知道果糖在體內的轉變過程，很有趣。還有，除了了解糖在體內的轉換外我也透過延伸閱讀知道糖不是只有壞處。
