Is Coffee good or bad? A critical view on the science behind it
喝咖啡的利与弊?对其科学内涵的批判性观点
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2019-08-11 22:16
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Coffee is a beloved drink (or fuel) for millions of people around the world. It’s also one of the most well-studied beverages in the world — so much so that it can be extremely confusing to navigate its scientific literature. It seems like every day there’s a new study on coffee’s health benefits but also, conversely, its downsides. Which begs the question: is coffee good or bad?

咖啡是全世界数百万人都喜爱的饮料(或燃料)。它也是世界上被研究得最透彻的饮料之一——以至于它在科学文献中的使用非常令人费解。似乎每天都有一项关于咖啡对健康好处的新研究,但相反,它也对健康有害。这引出了一个问题:咖啡究竟是好还是坏?

The black fuel that sends your metabolism into overdrive

这种黑色的燃料能让您进行极速的新陈代谢

Caffeine (1,3,7-trimethylxanthine), the main stimulant found in coffee — but also in tea, soft drinks, chocolate, and some nuts — has many metabolic effects. Besides caffeine, coffee contains other substances with important metabolic effects such as theobromine (main stimulant found in cocoas), theophylline (may be good for treating asthma), and chlorogenic acid (may slow down carbohydrate absorption).

咖/啡/因(1,3,7-三甲基黄嘌呤)是咖啡中的主要成分——还有茶,软饮料,巧克力和一些坚果——对代谢有许多影响。除咖/啡/因外,咖啡还含有其他具有重要代谢影响作用的物质,如可可碱(可可中含有的主要兴/奋/剂)、茶碱(可能有助于治疗哮喘)和绿原酸(可能减缓碳水化合物的吸收)。

One of the most familiar feelings people associate with coffee is “awakeness” — after all, so many people use coffee on a daily basis in their morning routines. Within 15 minutes of the first sip, caffeine is known to boost mental alertness and cognitive functioning, as well as enhancing physical performance by improving endurance and reaction time.

人们对咖啡最熟悉的感受之一就是“清醒”——毕竟,很多人每天都会在早晨的日常生活中饮用咖啡。在第一次啜饮的15分钟内,咖/啡/因可提高精神警觉性和认知功能,并通过改善耐力和反应时间来提升身体表现。

It does so by latching onto and blocking receptors in the brain for adenosine, a chemical which is produced by neurons throughout the day. When adenosine levels are high, the body’s metabolism slows down, priming you for sleep. With adenosine out of the way, the neurotransmitters dopamine and glutamate, which are natural stimulants generated in the brain, are free to do their magic. You start feeling more alert and awake, as a consequence.

这是通过锁定和阻断大脑中受体的腺苷来实现的,腺苷是一种全天由神经元产生的化学物质。当腺苷水平很高时,身体的新陈代谢会减慢,促进睡眠。随着腺苷的排除,神经递质多巴胺和谷氨酸,它们是大脑中产生的天然兴/奋/剂,可以自由地发挥自己的魔力。最终,你开始感到更加警觉,更加清醒。

But, as every coffee ‘addict’ knows, this effect lessens over time because of an annoying thing called tolerance. So you’ll need to do intake more and more caffeine to achieve the same level of stimulation from dopamine and glutamate.

但是,正如每个咖啡‘上瘾者’都知道的那样,这种效果随着时间的推移而减少,因为有一种叫做耐受的讨厌的作用。所以你需要摄入越来越多的咖/啡/因来达到多巴胺和谷氨酸的相同刺激水平。

What caffeine does to the body

咖/啡/因对身体的作用

While stimulating the nervous system, caffeine also signals fat cells to break down, releasing fatty acids in the bloodstream. This also means that the body has more glycogen available in the muscles to burn during a workout, enhancing endurance. In the same vein, caffeine has been found to influence the energy balance by increasing energy expenditure and decreasing energy intake, hence it can be a weight regulator for some people. It’s no surprise that caffeine is often found in weight loss products. Counter-intuitively, the increase in metabolism is less pronounced for obese individuals. One study, for instance, found that caffeine increased lipid oxidation by as much as 29% in lean women, while the increase was only about 10% in obese women. Again, the effects may be less pronounced in regular coffee consumers and decline with age. If the main reason you’re using coffee is for weight loss, you might want to alternate your patterns of consumption — for instance, use coffee for two weeks, stop for the next two weeks to prevent tolerance, and then reset.

在刺激神经系统的同时,咖/啡/因也可以指示脂肪细胞分解,释放出血液中的脂肪酸。这也意味着身体在锻炼期间肌肉中有更多的糖原可以燃烧,从而增强耐力。同样,人们已经发现咖/啡/因通过增加能量消耗和减少能量摄入来影响能量平衡,因此它可以是某些人的体重调节剂。在减肥产品中经常发现咖/啡/因并不稀奇。与直觉相反,肥胖个体的新陈代谢增加不太明显。例如一项研究发现,在较瘦的女性群体中,咖/啡/因使脂质氧化增加了29%,而对于肥胖女性则增加了约10%。同样,在常规咖啡消费者中效果可能不那么明显,并且效果会随着年龄的增长而下降。如果您使用咖啡的主要原因是减肥,您可能想要改变消费模式——例如,饮用咖啡两周后,在接下来的两周停止以防止产生耐受,然后循环这个过程。

Some studies show that drinking three or four cups of coffee a day could reduce your risk of developing type 2 diabetes by 25% compared to consuming no coffee or less than two cups daily. Caffeinated coffee may improve glycaemic metabolism by reducing the glucose curve and increasing the insulin response. But before you hurry to the supermarket to buy all the coffee on the shelves, bear in mind that there is a lot of conflicting information about coffee.

一些研究表明,与不喝咖啡或每天少于两杯相比,每天喝三到四杯咖啡可以将患2型糖尿病的风险降低25%。含咖/啡/因的咖啡可通过降低葡萄糖曲线和增加胰岛素反应来改善血糖代谢。但是,在你赶到超市疯狂购买咖啡之前,请记住有很多关于咖啡的相互矛盾的信息。

A 2017 study found five out the seven studies it analyzed concluded that caffeine intake increases blood glucose levels, and prolongs the period of high blood glucose levels in individuals with diabetes. Another study found that acute caffeine consumption in healthy individuals significantly decreased insulin sensitivity, potentially leading to high blood sugar. So drinking a lot of coffee (more than seven cups/day) may actually cause you to put on more weight and increase the risk of developing diabetes.

一项2017年的研究发现,在其分析的七项研究中,有五项研究得出结论,摄入咖/啡/因会增加血糖水平,并延长糖尿病患者的高血糖水平。另一项研究发现,健康个体的急性咖/啡/因摄入显着降低了胰岛素敏感性 ,可能导致高血糖。 因此,大量饮用咖啡(每天超过7杯)可能会导致您的体重和患糖尿病的风险增加。

An old idea is that you shouldn’t drink coffee if you have heart problems, but the opposite may be true. Drinking around four cups of coffee every day promotes the movement of a regulatory protein into mitochondria, which may prevent cardiovascular and cellular damage. An earlier report, published in 2017 in the journal Annual Review of Nutrition, analyzed the results of more than 100 coffee and caffeine studies, finding that coffee was associated with a probable decreased risk of cardiovascular disease.

有一个古老的想法,如果你心脏不好,那么你不应该喝咖啡,但事实恰恰相反,每天喝四杯咖啡可促进调节蛋白质进入线粒体,从而预防心血管和细胞损伤。2017年发表在《营养年度评论》期刊上的早期报告分析了100多项咖啡和咖/啡/因研究的结果,发现咖啡与可能降低的心血管疾病风险有关。

What’s less ambiguous is that coffee is the most widely used dietary source of antioxidants in the world. Antioxidants are important because they pair with so-called “free radicals”, which are molecules with unpaired electrons that can damage cells and DNA. Among the many antioxidants found in coffee, the most effective are hydrocinnamic acids and polyphenols. This antioxidation effect is thought to protect the body against aging and many diseases that are partly caused by oxidative stress, including liver disease, Parkinson’s, various types of inflammation, and even cancer.

还有不那么模棱两可的观点,咖啡是世界上使用最广泛的抗氧化剂膳食来源。抗氧化剂很重要,因为它们与所谓的“自由基”配对,后者是具有不成对电子的分子,可以破坏细胞和DNA。在咖啡中发现的许多抗氧化剂中,最有效的是氢化肉桂酸和多酚。这种抗氧化作用被认为可以保护身体免受衰老和许多部分由氧化应激引起的疾病,包括肝病, 帕金森病,各种类型的炎症,甚至癌症。

Effects can vary from person to person, hence the conflicting information

但效果因人而异,因此此类信息存在矛盾

Conflicting information about the effects of coffee abound. Until not too long ago, the World Health Organization classified coffee as “possibly” carcinogenic, but later reversed the statement stating that evidence for the association between coffee and cancer is inadequate. As mentioned earlier, the same conflicting evidence can be seen for cardiovascular disease. Perhaps the reason so many studies come up with so many different conclusions is that every person is different to a degree, especially in the way they metabolize substances.

有关咖啡影响的信息比比皆是。直到不久之前,世界卫生组织将咖啡归类为“可能”致癌物质,但后来推翻了咖啡与癌症之间关联的声明证据不足的声明。如上所述,心血管疾病可见相同的相互矛盾的证据。也许许多研究得出如此多的不同结论的原因是人类不同个体在某种程度上存在差异性,特别是在代谢物质的方式上。

According to researchers at the University of Toronto, one particular gene may have an important say in the matter. The gene identified by the researchers, called YP1A2, controls an enzyme that determines how quickly our bodies break down caffeine. Individuals who have a certain variant of the gene can metabolize caffeine four times faster than people who inherit one or more copies of the slow variant of the gene. Previously, the same team of researchers led by Ahmed El-Sohemy, a professor in the department of nutritional sciences at the University of Toronto, had studied 4,000 adults, including about 2,000 who had previously had a heart attack. The results suggested that ingesting four or more cups of coffee per day was associated with a 36% increased risk of a heart attack. However, when the participants were split into groups (fast metabolizers and slow metabolizers), the authors found that acute coffee intake was associated with increased heart attack risk only in the slow metabolizer group.

根据多伦多大学的研究人员的说法,一个特定的基因可能在这个问题上有重要的发言权。由研究人员鉴定的基因为YP1A2,它控制一种决定我们的身体分解咖/啡/因的速度的酶。具有该基因的某种变体的个体可以比继承该基因的慢变体的一个或多个同样基因的人代谢咖/啡/因慢四倍。此前,由多伦多大学营养科学系教授艾哈迈德·索赫米领导的同一研究小组研究了4000名成年人,其中包括大约2000名曾经患有心脏病的人。结果表明,每天摄入四杯或更多杯咖啡与心脏病发作风险增加36%有相关。然而,当参与者被分组(快速代谢者和慢代谢者)时,作者发现急性咖啡摄入仅与慢代谢组中的心脏病发作风险增加有关。

Slow metabolizers keep caffeine in their system for longer, offering it more time to trigger harmful effects such as heart attacks. On the other hand, fast metabolizers may allow antioxidants, polyphenols and coffee’s other healthful compounds to kick in without the side effects of caffeine because the stimulant is flushed out of the system fast.

代谢缓慢的人可以长时间将咖/啡/因保存在体内,让它有更多的时间来导致心脏病等有害影响。另一方面,代谢快的人可以允许抗氧化剂、多酚和咖啡中其他有益健康的化合物在没有咖/啡/因副作用的情况下被吸收,因为兴/奋/剂被迅速排出了系统。

And in all likelihood, there may be many other genetic and environmental factors contributing to differences in caffeine metabolism.

而且很有可能,还有许多其他遗传和环境因素导致了咖/啡/因代谢的差异。

Coffee seems to do more good than harm

咖啡似乎利大于弊

Many studies that investigate the health outcomes of caffeine can use different methodologies, demographics, or can simply be flawed. Overall, however, studies seem to point to net benefits of drinking coffee — although how fast you metabolize the stimulant seems to play a key role. An umbrella review published in the prestigious British Medical Journal — which included more than 200 meta-analyses of observational and interventional studies of coffee consumption and any health outcome — found that “coffee consumption was more often associated with benefit than harm.” Three to four cups of coffee reduced the risk of type 2 diabetes, metabolic syndrome, kidney stones, gout, and several types of cancer, including endometrial, skin, prostate and liver cancer. The only vulnerable group which the authors identified was pregnant women, who are at an increased risk of bone fracture.

许多调查咖/啡/因健康结果的研究可能会使用不同的方法,人口统计学,或者只是有缺陷。然而,总的来说,研究似乎指出了喝咖啡的净效益 - 尽管你代谢兴/奋/剂的速度似乎起着关键作用。在着名的《英国医学杂志上》发表的一份综合评论——其中包括200多项关于咖啡消费和任何健康结果的观察和干预研究的荟萃分析——发现“咖啡消费往往与利益相关而不是弊端。”三到四杯咖啡可以降低2型糖尿病、代谢综合征、肾结石、痛风和几种癌症的患病风险,包括子宫内膜癌、皮肤癌、前列腺癌和肝癌。作者确定唯一的咖啡弱势群体是孕妇,她们骨折的风险会增加。

“Coffee consumption seems generally safe within usual levels of intake, with summary estimates indicating largest risk reduction for various health outcomes at three to four cups a day, and more likely to benefit health than harm,” the researchers concluded.

研究人员得出结论:“咖啡摄入量在通常的摄入量水平下似乎总体上是安全的,总结估计表明,每天摄入三到四杯咖啡,能大大降低各种健康风险,利大于弊。”

Some die-hard fans might consider what I’m about to say next as heresy, but there is such a thing as too much coffee. In fact, you can even overdose (and risk dying) from too much caffeine — although that would be quite challenging to do on coffee alone. If you weigh 60 kg, you’d need to drink around 55 cups of coffee to overdose — but be aware that energy drinks have a high concentration of caffeine which makes it easy to overdose if you use them in quick succession. According to one study, there have been only 45 deaths related to caffeine reported between 1959 and 2010.

一些咖啡的铁杆粉丝可能会考虑我接下来要说的异端,但也有人会过量饮用咖啡。事实上,你甚至可以通过摄入过多咖/啡/因(并且存在死亡风险)导致过量使用——尽管单独喝咖啡会非常具有挑战性。如果你体重60公斤,你需要喝大约55杯咖啡才能到达到过量——但要注意能量饮料中含有高浓度的咖/啡/因,如果你连续喝的话就很容易过量。一项研究表明,1959年至2010年期间仅有45人死于咖/啡/因。

You don’t have to overdose to feel unpleasant side effects. Going above 400 mg daily, the recommended dose for adults, can cause jitteriness, insomnia, and irritability. So, moderation is key — just like with everything else in life. And if you actually decide to take a break, be prepared to face withdrawal symptoms such as feeling anxious, irritable, and drowsy. Luckily, these side effects are temporary and fade within 3 to 10 days.

您不必过量饮用以产生令人不快的副作用。成人的推荐剂量是每日400毫克,超过这个水平会引起抖动,失眠和烦躁。因此,适度才是关键——就像生活中的其他事物一样。如果您确实决定一段时间不喝咖啡,请准备好面对戒断症状,例如焦虑、烦躁和昏昏欲睡。幸运的是,这些副作用是暂时的,会在3到10天内消退。

Bottom line: evidence points to the fact that coffee does more good than harm, indicating that it can be part of a healthful diet.

总结:证据表明,咖啡确实利大于弊,这表明它可以成为健康饮食的一部分。

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