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Like opening the blinds and stepping into the shower, a cup of coffee gets people moving in the morning — in more ways than one. This satisfying brew revs energy levels with a dose of caffeine and, for many people, quickly and reliably jump-starts gut activity and an urgent need to poop.
就像打开百叶窗和冲淋浴一样，一杯咖啡能让人在早上振作起来——多方面的振作。这种令人满足的饮品通过咖啡因来提升人的能量水平，而且对许多人来说，它能迅速可靠地启动肠道活动和排便的迫切需求。
But given coffee’s popularity, it’s surprising that we know so little about how it affects the gastrointestinal tract, said Dr. Robert Martindale, a professor of surgery and the medical director for hospital nutrition services at Oregon Health and Science University.
但是，俄勒冈健康与科学大学外科教授、医院营养服务医疗主任罗伯特·马丁代尔说，令人意外的是，咖啡这么受欢迎，但我们对它的胃肠道影响其实知之甚少。
Some studies on the topic — which tend to be small, old and limited — have suggested that it’s probably not the caffeine that triggers the urge to go. One paper published in 1998, for instance, found that decaffeinated coffee had a similar stimulatory effect on the colon as caffeinated coffee, whereas a cup of hot water did not.
关于这个问题的研究往往是小型、陈旧和有限的，但其中一些表明，触发这种冲动的可能不是咖啡因。例如，1998年发表的一篇论文发现，低因咖啡和含咖啡因的咖啡对结肠有类似刺激作用，而热水则没有。
Coffee is a complex beverage containing more than 1,000 chemical compounds, many of which have antioxidant and anti-inflammatory properties. And determining how they affect the intestines is challenging.
咖啡是一种复杂的饮料，含有1000多种化合物，其中许多具有抗氧化和消炎的特性。确定它们如何影响肠道是很困难的。
One thing we do know is that coffee doesn’t affect everyone the same way. In one study published in 1990 in the journal Gut, 92 young adults filled out a questionnaire about how coffee affected their bowel habits; just 29 percent of the respondents said it “induced a desire to defecate,” and most of them — 63 percent — were female. (Though Dr. Martindale said that the percentage of people who have a bowel response after drinking coffee is likely much higher in the general population — he estimated that around 60 percent of his patients do — and he hasn’t noticed any differences between men and women.)
我们知道，咖啡对每个人的影响并不相同。1990年发表在《肠道》杂志上的一项研究中，92名年轻人填写了一份关于咖啡如何影响排便习惯的问卷。只有29%的受访者表示它能“诱发排便欲”，其中多数（63%）是女性。（但马丁代尔说，在一般人群中，喝完咖啡后出现排便反应者的比例可能要高得多——他估计他的病人中大约有60%是这样的——而且他没有发现男性和女性之间有任何差异。）
We also know that a gut response to coffee can happen fast. In the same study, some volunteers agreed to have a pressure-sensing probe inserted into their colon to measure intestinal muscle contractions before and after drinking a cup of Joe. Among those who said that coffee usually stimulated a bowel movement, the probe showed a significant increase in pressure within four minutes of drinking coffee, while the so-called nonresponders had no change in colon activity.
我们也知道，肠道对咖啡的反应会很快发生。在同一项研究中，一些志愿者同意在结肠中插入一个压力感应探针，以测量喝咖啡前后肠道肌肉的收缩情况。在那些说咖啡通常会刺激排便的人当中，在喝咖啡后四分钟内，探针显示的压力会显著增加；而自称无反应者的结肠活动没有变化。
That drinking a cup of coffee can stimulate the opposite end of the gastrointestinal tract within minutes means “it’s probably going through the gut-brain axis,” Dr. Martindale said. That is, the arrival of coffee in the stomach sends a message to the brain, which then “stimulates the colon to say, ‘Well, we’d better empty out, because things are coming downstream,’” he explained. The coffee itself would move through the intestines much more slowly, likely taking at least an hour to traverse the long path from the stomach through the small intestine and to the colon.
喝一杯咖啡可以在几分钟内就刺激胃肠道的另一端，这意味着“它可能会通过肠道-大脑轴，”马丁代尔说。也就是说，咖啡到达胃部后会向大脑发送信息，然后“刺激结肠说，‘好吧，我们最好清空所有东西，因为有东西要下来了，’”他解释说。咖啡本身通过肠道的速度会慢得多，可能需要至少一个小时才能走完从胃通过小肠到达结肠这段长长的路程。
While the mechanism remains murky, coffee’s effects on the gut may be helpful for some people, including those recovering from certain types of surgery. Impaired bowel function is common after abdominal surgeries, for instance, which can lead to bloating, pain and an inability to pass gas or tolerate food. A 2020 analysis combined the results of seven clinical trials and found that drinking coffee allowed patients who had undergone colorectal or gynecological surgery to tolerate solid foods an average of 10 and 31 hours sooner, respectively. Coffee also reduced the time to their first bowel movement, by an average of 15 to 18 hours.
虽然机制仍然很模糊，但咖啡对肠道的影响可能对一些人有帮助，包括从某些类型的手术中恢复的人。例如，腹部手术后肠道功能受损很常见，可能会导致腹胀、疼痛、无法排气或无法耐受食物。2020年的一项分析综合了七项临床试验的结果，发现喝咖啡可以让接受结肠、直肠手术和妇科手术的患者固体食物耐受分别平均提前10小时和31小时。咖啡还减少了他们术后第一次排便所需的时间，平均为15到18个小时。
Some people find that coffee causes an upset stomach and loose stools, as well as side effects linked to excess caffeine, like insomnia, anxiousness, heart palpitations and headache, Ms. Angelone added. The Food and Drug Administration says that it’s safe for most people to drink 400 milligrams of caffeine — the amount in about four or five cups of coffee — per day. Though keep in mind that people metabolize caffeine differently, so this threshold can vary from person to person. “Coffee is one of those things, unlike other foods, that if it bothers you, you know it,” Ms. Angelone said.
安吉罗还说，有些人发现咖啡会导致胃部不适和软便；还会产生与咖啡因过量相关的副作用，比如失眠、焦虑、心悸和头痛。美国食品和药物管理局表示，对大多数人来说，每天饮用400毫克的咖啡因是安全的——相当于四到五杯咖啡中的咖啡因含量。不过要记住，每个人对咖啡因的代谢情况是不同的，所以这个阈值因人而异。“咖啡不像其他食物，如果它让你感到不舒服，你就能感受到，”安吉罗说。
