When teenagers have spots, it’s not long before someone tells them they should eat less chocolate. Whether there’s any truth in this involves asking two questions: first, is there any evidence that people who eat chocolate are more likely to have acne; and second, is there a process by which ingesting chocolate could cause spots?
在青少年长痘后不久，一定会有人告诉他们该少吃点巧克力了。想要确定这样说是否正确，需要问两个问题：第一，有没有证据表明吃巧克力的人更易长痘；第二，从吃巧克力到长痘，这之中是否有一个过程？
I’ll begin with the second question. Spots occur when skin pores become blocked with sebum, the oily substance produced by tiny glands that lie within the skin. If the pore is partially blocked you get a blackhead. If it’s fully blocked you get a whitehead. All of us have millions of harmless bacteria living on our skin, and these can infect a blocked pore, causing a red lump to form – in other words a spot. If you get a lot of spots it is known as acne.
我要从第二个问题说起。皮肤中微小的腺体会分泌一种油性物质——皮脂，当毛孔被皮脂阻塞时就会长痘。如果毛孔被部分阻塞你就会长黑头，如果是全部阻塞你就会长粟粒疹。所有人的皮肤中都有成千上万的无害细菌，它们会使受阻塞的毛孔感染，形成一个红色的肿块——也就是一个包，如果你长了很多包，人们称其为痘痘。
If both your parents had acne when they were teenagers then you are more likely to have it too. The reason that adolescents are particularly prone to spots is that sebum-producing glands are highly sensitive to hormones. Acne usually reduces by the time you become an adult, but a small percentage of people find it persists. Even in adults, fluctuations in hormone levels continue to have an impact, for instance, some women find they get more spots in the run-up to their period or when they’re pregnant.
如果你的父母在青少年时期都长过痘痘，那么你长痘痘的可能就更大了。青少年特别容易长痘的原因在于皮脂分泌腺体对激素水平十分敏感。当你成人后，痘痘的数量通常就会减少，但对于一小部分人而言，痘痘还会继续存在。即便是成人，激素水平的波动也会继续发挥作用，比如，一些女性发现她们在生理期之前或者怀孕期间会长更多痘痘。
But back to the question, is there a process by which chocolate could exacerbate acne? There are several theories. One is that since chocolate is fatty it could increase the level of soluble fat in the bloodstream, which could in theory lead to the production of more sebum, and therefore more blocked pores. There is also a suggestion that large quantities of chocolate could raise insulin levels in the bloodstream, altering the levels of some hormones, again leading to an increase in sebum production.
回到那个问题上来，从吃巧克力到长痘，这之中是否有一个过程？有这样几种理论。一种理论认为由于巧克力中含有脂肪，所以吃巧克力会增加血液中可溶性脂肪含量，理论上，这会导致皮脂分泌增多，因此就会有更多毛孔阻塞。另有证据表明大量食用巧克力会增加血液中胰岛素的含量，由此改变某些激素的水平，也会导致皮脂分泌的增多。
Sweet study
甜度研究
The theories sound plausible, but what happens in practice? A systematic review from 2005 found just three studies looking at chocolate, all conducted several decades ago. One study found that the quantity of chocolate, milk and roasted nuts university students ate made no difference to the severity of acne. But the sample was small and there was no control group, making it hard to draw many conclusions from this study.
这些理论听上去似乎是合理的，但事实是怎样的呢？2005年的一次系统性回顾发现关于巧克力的研究只有3项，还都是在几十年前展开的。其中一项研究认为大学生们食用的巧克力、牛奶和烤坚果数量与长痘痘的严重程度没有关系。但是这项研究的样本容量小，也没有设置对照组，我们很难从中得到很多结论。
In 1969, a placebo-controlled study conducted in patients visiting an acne clinic and men in prison also found chocolate made no difference to acne. Now you might be wondering what a chocolate placebo looks like, and where you can get one. The participants were given chocolate bars with the same fat and sugar content as ordinary chocolate, but with lower levels of cocoa. So this study only tells us that cocoa makes no difference to acne, it tells us little if not nothing about fat and sugar. What’s more, the prisoners and patients only ate chocolate for four weeks. Medication for acne usually takes two or months before an improvement is seen, so this might not have been long enough to show chocolate’s effect on the skin.
1969年的一项安慰剂控制研究也认为吃巧克力与长痘痘无关，这项研究是在痤疮门诊病人和监狱男囚中展开的。现在，你可能会好奇巧克力安慰剂长什么样以及在哪里可以买到它。研究的参与者得到的巧克力与普通巧克力的脂肪和糖分含量相同，但可可的含量低一些。所以这项研究仅仅告诉我们可可与长痘无关，而对于脂肪和糖分，它什么都没说，如果说了，也是极少的。另外，犯人们和病人们都只吃了4周的巧克力。而使用祛痘药物两周或数月后情况才会改善，所以4周的时间不足以揭示吃巧克力对皮肤的作用。
The third study doesn’t reveal much more information. Eight students ate a bar of chocolate on two consecutive days, and four of them developedas many as five spots. With a sample this tiny, it’s impossible to know whether those five spots would have appeared anyway, regardless of what the students had eaten.
第三项研究也没有展示更多的信息，8名学生连续两天，每天吃一块巧克力，其中4人长出了多达5个痘痘。是不是无论他们吃什么，这五个痘痘都会出现呢？样本容量如此之小，我们无法知道这个问题的答案。
So we can’t yet pin the blame on chocolate, but how about diet in general? A study from back in 1956 on more than two thousand British soldiers suggested a possible link with diet – it found that 20-to-40-year-old soldiers with acne were likely to weigh more than teenage soldiers without.
所以现在我们还不能把长痘归咎于吃巧克力，但是一般的饮食习惯对长痘会有影响吗？1956年进行的一项以2000名英国士兵为样本的研究表明，长痘和饮食之间可能存在联系——这项研究发现：与十几岁不长痘的士兵相比，那些处于二十到四十岁之间长痘的士兵要更重一些。
But for many years inconclusive studies meant that any link between food and acne was at best unproven, and at worse a myth. Then in 2002 came the intriguing finding that no one in non-westernised populations in New Guinea and Paraguay had acne. Suddenly diet was back on the agenda. Of course there is the possibility it is genetics that is protecting these populations from acne, but if diet does make a difference, then we need to know which kinds of foods in industrialised countries are having the biggest impact on acne. Is it the amount of fat consumed that matters, or sugar, or as some have suggested, the speed at which the sugar breaks down (high versus low glycaemic diets)?
但是多年来，无结果的研究意味着饮食与长痘之间的任何联系，往好了说，还没有得到证明，往坏了说，还是一个迷。而后，在2002年，人们有了一个有趣的发现：在未西化的新几内亚和巴拉圭人中，没有一个人长痘。突然之间，饮食回到了人们的议程之中。当然，有可能是基因使这些人不长痘痘，但如果饮食真的有影响，那么我们需要知道在工业化国家究竟是哪些食物对长痘痘的影响最大。是不是与脂肪和糖分的摄取量有关？亦或是像有些人提出的那样，与糖分分解的速度有关（高血糖食物Vs低血糖食物）？
Again, reviews can’t help us – they conclude that there’s not enough evidence to know what is happening. A review in 2009 looked at 21 observational studies and six clinical trials and concluded that dairy products made a difference, but not chocolate in particular. However, before you think about cutting out dairy products, bear in mind that this review included some trials with very few participants and no control groups. As the authors of a review published last year point out, some of these studies simply asked people what they believe exacerbates their acne, rather than what is clinically proven to do so. This is not a reliable method because we all have a tendency to look for links if we have heard they might be true.
这一次文献综述还是帮不了我们——它们的结论是没有足够的证据能够解释这一切。2009年的一份综述，着眼于21项观察研究和6个临床试验，得出乳制品与长痘有关，但巧克力不是特例的结论。然而，在你打算停止食用乳制品之前，你要记住，这份综述中的一些试验的参与者非常少，也没有对照组。正如去年发表的一份综述的作者所指出的那样，这当中的一些研究仅仅是询问人们他们认为是什么导致他们长痘痘，而不是通过临床试验来证明。这样的方法是靠不住的，因为如果我们听说某些联系是真的，我们就会自然而然地去寻找这样的联系。
The fact is that regardless of what people eat, their acne usually gets better when they leave their teens. So if we are ever to discover the answer, what we need are well-designed prospective studies. And that means tracking people across many months or even years while assessing their chocolate consumption and the severity of their acne. Ideally they need to be randomised either to eat lots of chocolate or none at all. The trouble is that when volunteers get no say as to which group they end up in, this might not be a study that people rush to join.
事实是，人们无论吃什么，当他们告别青春期之后，长痘的情况通常会好转。因此，如果我们想要找到答案，我们需要一些精心设计的，有前瞻性的调查。这意味着跟踪调查对象数月甚至数年，同时评估他们巧克力的摄入量和痘痘的严重程度，理想的情况是：吃很多巧克力和一点都不吃的人数都很随机。问题是，如果志愿者们无权决定自己最终处在哪一组，他们可能不会那么积极地去参加这项研究。
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