经济学人:感染病毒时进食 感染细菌时禁食

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　　An old wives’ tale gets some support from medical science. 无稽之谈获医学证实。

　　Whether it is best to feed a fever and starve a cold, or vice² versa, varies with the grandparent being asked. 要说是发烧时宜吃，伤风时宜饿呢，还是反之为佳？不同的祖父母回答是不一样的。

　　Medicine has decided³ that it is always a bad idea to deny food to the ill. 医疗界已经判定，生病时拒绝进食总非良策。

　　Now a new study suggests that by ignoring such old wives’ tales, medics may have missed a trick. 现有一项新研究表明，若忽视这类无稽之谈，医疗人员可能会错过机会。

　　A paper just published in Cell by a team of researchers led by Ruslan Medzhitov at Yale University  由耶鲁大学鲁斯兰·麦哲托夫带领的团队近日在《细胞》上发表的研究表明，

　　suggest that force-feeding mice infected with influenza⁴ keeps them alive—but doing the same to mice with bacterial⁵ infections is fatal. 患有流感的老鼠受到强行喂食尚能活命，而对有细菌感染的老鼠却是致命的。

　　Dr Medzhitov was inspired by experiments conducted not by medics, but by zoologists⁶. 麦哲托夫博士受到动物学家 (而非医生) 所做的实验启发。

　　Most animals instinctively⁷ respond to infection by cutting back on food,  大多数动物受到感染后，会本能地减少进食，

　　and a slew⁸ of studies in recent years have shown that when diseased animals are force-fed they are more likely to die than if they are allowed to abstain⁹. 并且近年来大量研究表明，强制给生病的动物喂食比允许其抑制进食更易致死。

　　But Dr Medzhitov wondered whether that held true for all types of disease. 但麦哲托夫博士好奇这是否适用于各类疾病。

　　To investigate, he and his team infected one group of mice with a murine influenza virus, and the other with Listeria monocytogenes, a bacterium that causes food poisoning. 为了进一步调查，麦哲托夫博士和他的团队使一组老鼠感染流感病毒，另一组感染能引发食物中毒的李斯特菌。

　　Some mice in each group were force-fed rodent¹⁰ chow, while others were force-fed nutrition-free saline. 每组中，给一部分老鼠强迫喂食鼠类饲料，而给另一部分老鼠注射无营养的生理盐水。

　　Every single mouse that was infected with the bacterium died if they were given food, but half survived on the saline. 感染细菌又被强迫喂食物的老鼠全部死亡，而被注射生理盐水的老鼠存活率达到一半。

　　The results of the viral infection were less stark¹¹, but still clear: 77.8% of infected mice survived if given food, but only 10% did so when given saline. 虽然病毒实验结果不那么残酷，但依然分明：其中被强迫喂食的老鼠存活率77.8%，而被注射生理盐水的老鼠存活率仅为10%.

　　One clue as to what might be going on lies in the fact, identified in earlier research, that cells infected with bacteria often prefer to burn fat instead of glucose¹², their usual fuel. 导致这个结果可能的原因之一就在于受细菌感染的细胞通常倾向于燃烧脂肪而非葡萄糖 (平常的燃料)，这也得到早期研究的证实。

　　Further experiments led the team to confirm that glucose specifically was the key to survival in both viral and bacterial infections. 进一步的实验使团队确定，葡萄糖在病毒感染和细菌感染中起到了性命攸关的作用。

　　As with the rodent chow, mice with bacterial infections that were fed glucose died. 对感染细菌的老鼠喂食物或葡萄糖都致死。

　　But infected mice fed a version of glucose that they could not metabolise lived. 但当感染细菌的老鼠被喂食一类无法参与新陈代谢的葡萄糖时反而存活。

　　Again, those results were nearly reversed in mice suffering from a viral infection. 然而，受到病毒感染的老鼠结局几乎相反。

　　All of those fed the unusable variant¹³ of glucose died within ten days; 40% of those fed the ordinary stuff survived. 被喂食无法食用的变异葡萄糖的老鼠在10天之内全部死亡，喂食普通食物的老鼠中则有40%存活下来。

　　The glucose seemed to make no difference to the bugs¹⁴, nor to the immune systems of the mice. 葡萄糖似乎对轻微的传染病和老鼠的免疫系统没有什么影响。

　　Instead, it altered the biology of the infected cells. 相反，它转变了受感染细胞的机理。

　　In viral infections, many infested¹⁵ cells were committing suicide, a cellular¹⁶ scorched-earth strategy designed to slow the spread of the virus. 在病毒感染中，许多受感染的细胞都在自杀，这种焦土政策旨在减缓病毒的传播。

　　Providing glucose seemed to bolster¹⁷ their ability to fight the infection without resorting to such drastic measures. 而葡萄糖似乎只想要加强他们对抗感染的能力，而非诉诸于自杀这种极端的措施。

　　The opposite was true for bacteria. Burning fat protected infected mice. 相反，葡萄糖对细菌感染影响重大。燃烧脂肪保护了受感染的老鼠。

　　But swamping the cells with glucose caused them to produce prodigious¹⁸ quantities of highly reactive chemicals known as free radicals¹⁹, which damage cells. 但给细胞灌满葡萄糖会使它们产生数量庞大的高度活跃化学物质，即破坏细胞的自由基。

　　That collateral²⁰ damage made survival less likely. 这种附带损害使老鼠更难存活。

　　The precise biological details of why glucose is good for viral infections and bad for bacterial ones are not yet known. 葡萄糖对病毒感染有益却对细菌感染有害的具体生物学细节还尚未可知。

　　And Dr Medzhitov’s results will have to be tested in humans before medics can apply them. 在医护人员运用研究结果之前，麦哲托夫博士仍需要做临床试验。

　　But they are a useful reminder²¹ that there is sometimes genuine wisdom hidden in folksy homilies. 但这些成果依然有效地提醒人们：有时候民间俗语中还是蕴含着大智慧的。

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