Think turkey tryptophan makes you sleepy? Think again
(The Conversation)Every Thanksgiving, myths of the quasi-magical powers of tryptophan rise again.
There's the turkey/drowsiness myth: Eating lots of juicy turkey meat supposedly makes people feel tired because it contains an amino acid called tryptophan. This molecule travels into the brain, where it's converted into a neurotransmitter called serotonin, which in turn is converted into a hormone called melatonin. Voila! Sleepiness.
But science and the internet agree: It's not the turkey's tryptophan to blame for your post-feast nap. All protein sources, and even vegetables, contain some tryptophan; turkey isn't at all special in this regard.
So the sleepiness myth of turkey may be fading, but other legends around tryptophan's effects in the brain are taking hold. Some people are eyeing tryptophan supplements as an unconventional treatment for depression. Others are curious whether eating foods that are high or low in tryptophan could be useful for influencing mood. Recently, some scientists have even proposed that gut bacteria are driving changes in emotion by producing or breaking down tryptophan.
This tryptophan/mood connection is an area of ongoing research. And while some are captivated by tryptophan's potential, it's not clear whether the excitement is warranted.
Looking for a tryptophan link to mood
There is some scientific evidence that eating tryptophan can alter your mood.
For example, back in 2000, researchers found that when people ate an isolated protein that was very high in tryptophan, they felt less stress while doing math problems.
However, placebo-controlled clinical trials haven't, in general, shown much of a connection. A few studies have found that supplementing with pure tryptophan provided little to no benefit for people with depression. Some studies have even looked at what happens when you remove tryptophan from people's diets, but also found little to no effect.
So what explains the mixed results?
Serotonin itself still holds mysteries
Alongside human studies, the biology of tryptophan has been well studied in rodents. Research in the early 1970s showed that taking tryptophan supplements can boost serotonin, a neurotransmitter that was historically associated with feelings of well-being and happiness.
Since then, scientists have learned lots of interesting facts about serotonin. For example, there are 14 separate receptors for serotonin, and they're found all over the brain.
Researchers have learned how to affect this system with drugs, but not with much precision. For example, drugs like the antidepressant selective serotonin reuptake inhibitors -- more widely known as SSRIs -- don't target individual receptors and they don't restrict themselves to particular brain regions. Instead, SSRIs, the best-known of which is Prozac, bluntly boost serotonin everywhere.
This non-specificity is why, in my mind, it's hard to believe that SSRIs work at all. Here's an analogy: Say you're Jeff Bezos and you want to increase Amazon's revenue by speeding up your deliveries. So you decide to crank up the speed on all delivery vehicles. From now on, every truck will boost its speed by 5%. It may be a stroke of logistical genius, or it may, perhaps more likely, end up in chaos. Like ramping up serotonin all over the brain, this blunt approach might not be ideal.
Analogies aside, whether SSRIs affect people's moods is an experimental question, and some research has supported the idea that these drugs work. However, especially lately, their effectiveness has come under intense scrutiny. Some recent analyses cite 30 years' worth of studies and question the clinical value of SSRIs, while others maintain that these drugs improve the symptoms of depression.
It's complicated, and there's still some disagreement, but most psychiatrists agree that SSRIs are not effective for everyone. These drugs are not psychiatric-cure-alls.
More chemical fine-tuning for mood
In light of all this, I've often found myself asking whether psychiatric researchers needed 73 studies looking at whether tryptophan depletion has an impact on mood.
When it comes to understanding connections between gut bacteria and the brain, or the bigger challenge of understanding and treating mental illness, should researchers really still be thinking about tryptophan?
It's seems true that, similar to SSRIs, boosting tryptophan has a broad impact on serotonin. It's definitely possible that cranking up serotonin can influence mood, and that therefore boosting tryptophan could do the same. But it's also possible that to manipulate something as complicated as human emotion requires a little more nuance.
Psychiatric research has long been moving away from the idea that your brain is a bag of chemicals; modern neuroscientists are asking for a little more specificity. From this perspective, I'm skeptical of the notion that tryptophan is the depression remedy psychiatry needs. Not only has experimental research found fairly weak results, but the theory itself isn't very compelling.
Serotonin, seemingly full of psychiatric possibility, has long fascinated psychiatric researchers. But what the past half century seems to have demonstrated is that the neuroscience of human emotion is not simple. To promote lasting changes in mental health, scientists may need a little more reverence for the complex emotional beings that we all are.
So no, a big turkey dinner, as filled with delicious tryptophans as it might be, will likely not be the neurochemical driver for your mood on Thanksgiving.
认为火鸡色氨酸让你昏昏欲睡？再想想
（对话）每个感恩节，色氨酸的准魔法力量的神话再次兴起。
有火鸡/困倦神话：据说吃大量多汁的火鸡肉会使人感到疲倦，因为它含有一种叫做色氨酸的氨基酸。这种分子进入大脑，在那里转化为一种叫做血清素的神经递质，而血清素又转化为一种叫做褪黑激素的激素。瞧！困倦。
但科学和互联网都同意：不是火鸡的色氨酸是导致您餐后小睡的罪魁祸首。所有蛋白质来源，甚至蔬菜，都含有一些色氨酸；土耳其在这方面一点也不特别。
因此，火鸡的困倦神话可能正在消失，但其他关于色氨酸对大脑影响的传说正在流行。有些人将色氨酸补充剂视为一种非常规的抑郁症治疗方法。其他人很好奇食用色氨酸含量高或低的食物是否有助于影响情绪。最近，一些科学家甚至提出肠道细菌通过产生或分解色氨酸来推动情绪的变化。
这种色氨酸/情绪联系是一个正在进行的研究领域。虽然有些人对色氨酸的潜力着迷，但目前尚不清楚这种兴奋是否值得。
寻找色氨酸与情绪的联系
有一些科学证据表明，吃色氨酸可以改变你的情绪。
例如，早在 2000 年，研究人员就发现，当人们食用一种色氨酸含量非常高的分离蛋白质时，他们在做数学题时会感到压力较小。
然而，安慰剂对照的临床试验一般没有显示出很大的联系。一些研究发现，补充纯色氨酸对抑郁症患者几乎没有好处。一些研究甚至研究了当你从人们的饮食中去除色氨酸时会发生什么，但也发现几乎没有影响。
那么如何解释混合结果呢？
血清素本身仍然是个谜
除了人类研究，色氨酸的生物学在啮齿动物中也得到了很好的研究。 1970 年代初期的研究表明，服用色氨酸补充剂可以促进血清素的增加，血清素是一种历史上与幸福感和幸福感有关的神经递质。
从那时起，科学家们已经了解了许多关于血清素的有趣事实。例如，有 14 种不同的血清素受体，它们遍布整个大脑。
研究人员已经学会了如何用药物影响这个系统，但不是很精确。例如，抗抑郁药选择性血清素再摄取抑制剂（更广为人知的 SSRIs）等药物不针对单个受体，也不会将自身限制在特定的大脑区域。相反，SSRIs，其中最著名的是百忧解，直言不讳地在任何地方增加血清素。
这种非特异性就是为什么，在我看来，很难相信 SSRI 有效。打个比方：假设您是杰夫·贝佐斯（Jeff Bezos），您想通过加快交货速度来增加亚马逊的收入。因此，您决定加快所有送货车辆的速度。从现在开始，每辆卡车都将提高5%的速度。这可能是后勤天才的一击，或者更有可能最终陷入混乱。就像在整个大脑中增加血清素一样，这种生硬的方法可能并不理想。
撇开类比不谈，SSRIs 是否会影响人们的情绪是一个实验问题，一些研究支持这些药物有效的观点。然而，尤其是最近，它们的有效性受到了严格的审查。最近的一些分析引用了 30 年的研究并质疑 SSRIs 的临床价值，而其他人则坚持认为这些药物可以改善抑郁症的症状。
这很复杂，仍然存在一些分歧，但大多数精神病学家都同意 SSRI 并非对每个人都有效。这些药物不是精神治疗万能药。
对情绪进行更多化学微调
鉴于所有这些，我经常发现自己在问精神病学研究人员是否需要 73 项研究来研究色氨酸消耗是否会影响情绪。
当谈到理解肠道细菌和大脑之间的联系，或者是理解和治疗精神疾病的更大挑战时，研究人员真的应该还在考虑色氨酸吗？
与 SSRIs 类似，增加色氨酸对血清素有广泛影响，这似乎是真的。增加血清素肯定有可能影响情绪，因此增加色氨酸也可以起到同样的作用。但也有可能操纵像人类情感这样复杂的东西需要更多的细微差别。
长期以来，精神病学研究已经摆脱了大脑是一袋化学物质的观点。 现代神经科学家要求更具体一些。 从这个角度来看，我对色氨酸是精神病学所需的抑郁症治疗方法持怀疑态度。 不仅实验研究发现了相当薄弱的结果，而且理论本身也不是很有说服力。
血清素似乎充满了精神病学的可能性，长期以来一直让精神病学研究人员着迷。 但过去半个世纪似乎已经证明，人类情感的神经科学并不简单。 为了促进心理健康的持久变化，科学家们可能需要对我们所有人的复杂情感存有更多的敬畏。
所以不，一顿丰盛的火鸡晚餐，尽管充满了美味的色氨酸，但可能不会成为你感恩节心情的神经化学驱动因素。
