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.

This communication between the stomach, brain and colon, called the gastrocolic reflex, is a normal response to eating. But coffee seems to have an outsize effect; one study published in 1998 found that eight ounces of coffee stimulated colonic contractions similar to those induced by a 1,000-calorie meal. Researchers have hypothesized that coffee’s gut-brain messaging is likely caused by one or more of coffee’s many chemicals, and perhaps mediated by some of our own hormones that play important roles in the digestive process, like gastrin or cholecystokinin — both of which can spike after coffee drinking.

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。

“A couple of sips of coffee can do it. It doesn’t take much,” said Dr. Martindale, who routinely offers his patients a cup of coffee the morning after surgery.

“喝几口咖啡就能做到。并不需要太多，”马丁代尔说，他通常会在术后的早上为病人提供一杯咖啡。

Dr. Martindale also suggests coffee, along with other dietary changes, when he counsels patients with chronic constipation. And he said it’s not uncommon for patients who have given up coffee for one reason or another to tell him, “Doc, I can’t go to the bathroom without a coffee.”

在为慢性便秘患者提供咨询服务时，马丁代尔也建议他们在改变饮食习惯的同时喝咖啡。他说，经常有因为种种原因戒掉咖啡的病人告诉他，“医生，我不喝咖啡就没法排便。”

Sonya Angelone, a registered dietitian and spokeswoman for the Academy of Nutrition and Dietetics, cautioned against relying too much on coffee to stay regular. If someone is constipated, “it is not because they have a deficiency of coffee,” she said. Ms. Angelone recommends eating more fruits and vegetables, which are high in fiber, as well as increasing fluid intake and physical activity to address constipation. “What I find for a lot of people is they don’t start off with a fiber punch in the morning,” she said. Brewed coffee contains a small amount of fiber, about one gram per eight-ounce cup.

注册营养师、美国营养与饮食学会的发言人桑娅·安吉罗警告说，不要过度依赖咖啡来维持排便规律。她说，如果有人便秘，“并不是因为他们缺乏咖啡。”安吉罗建议多吃富含纤维的水果和蔬菜，并增加液体摄入量和体育活动来解决便秘问题。她说：“我发现，很多人早上起床时都不会摄入膳食纤维。”煮好的咖啡中含有少量纤维，大约每230毫升咖啡中含有1克纤维。

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.

But for the rest of us, coffee can be part of a comforting morning routine, waking us up in a multitude of ways.

但对我们其他人来说，咖啡可以成为一种舒适的晨间习惯，以多种方式唤醒我们。