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  3. (1) The salt equation taught to doctors for more than 200 years is not hard t

(1) The salt equation taught to doctors for more than 200 years is not hard t

游客2024-11-06  6
问题    (1) The salt equation taught to doctors for more than 200 years is not hard to understand. The body relies on this essential mineral for a variety of functions, including blood pressure and the transmission of nerve impulses. Sodium levels in the blood must be carefully maintained. If you eat a lot of salt—sodium chloride—you will become thirsty and drink water, diluting your blood enough to maintain the proper concentration of sodium. Ultimately you will excrete much of the excess salt and water in urine. The theory is intuitive and simple. And it may be completely wrong.
   (2) The research, published recently in two dense papers in The Journal of Clinical Investigation, contradicts much of the conventional wisdom about how the body handles salt and suggests that high levels may play a role in weight loss.
   (3) The findings have stunned kidney specialists. "This is just very novel and fascinating," said Dr. Melanie Hoenig, an assistant professor of medicine at Harvard Medical School. "The work was meticulously done. "
   (4) Dr. James R. Johnston, a professor at the University of Pittsburgh, marked each unexpected finding in the margins of the two papers. The studies were covered with scribbles by the time he was done. "Really cool," he said, although he added that the findings need to be replicated.
   (5) The new studies are the culmination of a decades-long quest by a determined scientist, Dr. Jens Titze, now a kidney specialist at Vanderbilt University Medical Center and the Interdisciplinary Center for Clinical Research in Erlangen, Germany.
   (6) In 1991, as a medical student in Berlin, he took a class on human physiology in extreme environments. The professor who taught the course worked with the European space program and presented data from a simulated 28-day mission in which a crew lived in a small capsule. The main goal was to learn how the crew members would get along. But the scientists also had collected the astronauts’ urine and other physiological markers. Titze noticed something puzzling in the crew members’ data: Their urine volumes went up and down in a seven-day cycle. That contradicted all he’d been taught in medical school: There should be no such temporal cycle.
   (7) In 1994, the Russian space program decided to do a 135-day simulation of life on the Mir space station. Titze arranged to go to Russia to study urine patterns among the crew members and how these were affected by salt in the diet. A striking finding emerged: a 28-day rhythm in the amount of sodium the cosmonauts’ bodies retained that was not linked to the amount of urine they produced. And the sodium rhythms were much more pronounced than the urine patterns. The sodium levels should have been rising and falling with the volume of urine. Although the study wasn’t perfect—the crew members’ sodium intake was not precisely calibrated (校准) —Titze was convinced something other than fluid intake was influencing sodium stores in the crew’s bodies. The conclusion, he realized, "was heresy. "
   (8) In 2006, the Russian space program announced two more simulation studies, one lasting 105 days and the other 520 days. Titze saw a chance to figure out whether his anomalous findings were real. In the shorter simulation, the cosmonauts ate a diet containing 12 grams of salt daily, followed by 9 grams daily, and then a low-salt diet of 6 grams daily, each for a 28-day period. In the longer mission, the cosmonauts also ate an additional cycle of 12 grams of salt daily. Like most of us, the cosmonauts liked their salt. Oliver Knickel, 33, a German citizen participating in the program who is now an automotive engineer in Stuttgart, recalled that even the food that supplied 12 grams a day was not salty enough for him. When the salt level got down to 6 grams, he said, "It didn’t taste good. "
   (9) The real shocker came when Titze measured the amount of sodium excreted in the crew’s urine, the volume of their urine, and the amount of sodium in their blood. The mysterious patterns in urine volume persisted, but everything seemed to proceed according to the textbooks. When the crew ate more salt, they excreted more salt: the amount of sodium in their blood remained constant, and their urine volume increased. "But then we had a look at fluid intake, and were more than surprised," he said. Instead of drinking more, the crew were drinking less in the long run when getting more salt. So where was the excreted water coming from? "There was only one way to explain this phenomenon," Titze said. "The body most likely had generated or produced water when salt intake was high. "
   (10) To get further insight, Titze began a study of mice in the laboratory. Sure enough, the more salt he added to the animals’ diet, the less water they drank. And he saw why. The animals were getting water— but not by drinking it. The increased levels of glucocorticoid hormones (糖皮质激素) broke down fat and muscle in their own bodies. This freed up water for the body to use. But that process requires energy, Titze also found, which is why the mice ate 25 percent more food on a high-salt diet. The hormones also may be a cause of the strange long-term fluctuations in urine volume.
   (11) Scientists knew that a starving body will burn its own fat and muscle for sustenance. But the realization that something similar happens on a salty diet has come as a revelation.
   (12) People do what camels do, noted Dr. Mark Zeidel, a nephrologist at Harvard Medical School who wrote an editorial accompanying Titze’s studies. A camel traveling through the desert that has no water to drink gets water instead by breaking down the fat in its hump.
   (13) One of the many implications of this finding is that salt may be involved in weight loss. Generally, scientists have assumed that a high-salt diet encourages a greater intake of fluids, which increases weight. But if balancing a higher salt intake requires the body to break down tissue, it may also increase energy expenditure.
   (14) Still, Titze said he would not advise eating a lot of salt to lose weight. If his results are correct, more salt will make you hungrier in the long run, so you would have to be sure you did not eat more food to make up for the extra calories burned. And, Titze said, high glucocorticoid levels are linked to such conditions as osteoporosis (骨质疏松症), muscle loss, Type 2 diabetes and other metabolic (新陈代谢的) problems. [br] It can NOT be inferred from the two studies announced in the same year that______.
选项 A、Titze wanted to verify his findings in these two studies
B、astronauts in the longer simulation had higher salt intake every day
C、Knickel was unsatisfied with all the salt levels offered in food
D、subjects were getting water not by drinking it when eating more salt
答案 B
解析 推理判断题。根据题干提示定位至第八段和第九段。第八段第三句提到在持续时间较短的那项模拟中，宇航员每天的饮食含有12克盐，接着是每天9克，然后是每天6克的低盐饮食，每个阶段为期28天。紧接着第四句指出，在持续时间较长的那项任务中，宇航员还多了一个每天摄人12克盐的饮食周期。由此可知，在两项任务中，宇航员们每天的食盐摄人量并没有区别，只是在持续时间较长的任务中，宇航员们多了一个每天摄入12克盐的饮食周期，B与原文表述不符，故为答案。第八段前两句提到，2006年，俄罗斯太空计划又宣布了两项模拟研究，一项持续105天，另一项持续520天，蒂策看到了一个机会，可以去弄清楚他那些异常研究结果的真假。由此可知，蒂策想要通过这两项研究验证其研究结果，故排除A；第八段第六句指出，参加了该项目的33岁德国公民奥利弗·科尼克尔回忆说，即使是每天提供了12克盐的食物，对他而言还是不够咸，这表明科尼克尔对食物里提供的最高盐量12克都不满意，由此可知，他对食物里提供的所有盐量都不满意，故排除c；第九段第五句提到蒂策发现当摄人更多盐分时，长期来看，全体宇航员非但没有喝更多的液体，反而喝得更少，该段第八句则指出蒂策认为当盐摄入量偏高时，身体很可能已经造水或产水了，由此可知，当摄入更多盐分时，实验对象并不是靠饮水来获得水分，故排除D。
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