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Episode 4: MSG The Nugent Report
The Nugent Report the science behind health and nutrition. Welcome to this episode of The Nugent Report, a definitive source for objective information on health and nutrition. Featuring Dr. Steve Nugent, the renowned psychologist, author, public speaker and expert on science, health, wellness and nutrition. Be sure to visit our website at ‘drnugen.com’ and follow us on Facebook, twitter and Instagram @TheNugentReport.
Steve Nugent: Hello and welcome to another episode of The Nugent Report. On this Nugent Report, we’re going to be talking about MSG (Monosodium Glutamate). A poll was taken on The Nugent Report Facebook page and the majority of the respondents said, they wanted to hear a podcast or see a blog on MSG. Well, I wasn’t really planning on this, but this is what my subscribers wanted so, so be it. If you’re sensitive to MSG or at least you believe you are, then you already have a good idea of what it is but not everyone does. So, let’s start by explaining what MSG is.
MSG is an abbreviation for Monosodium Glutamate and it’s commonly used as a flavor enhancer in many foods. From Bouillon cubes to canned vegetables. Believe it or not, MSG was first isolated by a Japanese scientist back in 1908. He was researching a particular flavor which is found in a seaweed an edible seaweed, which is called Kombu. And he was successful in his effort. So, it’s been around for a long time. Chemically, it’s a sodium salt of glutamic acid. Glutamic acid is a non-essential amino acid and that means it occurs naturally in the body. It’s required for building proteins in your body. It’s found in many different types of animal and plant proteins.
It also is a neurotransmitter, so that makes it pretty important and it’s required for ammonia metabolism. So, please understand that glutamic acid is not MSG. I get that question a lot. So, they’re not the same thing. So, MSG is a sodium salt of glutamic acid. The US FDA says that, MSG is safe but some disagree. Some have even implied that MSG could lead to brain damage. I must point out that there is no peer-reviewed science literature to support that. Remember that The Nugent Report is dedicated to bringing you objective science. That means you’re going to get both sides of this story.
The people who report various symptoms associated with MSG are often said to have Chinese Restaurant Syndrome or CRS. Because it’s most commonly used in Chinese food. The first paper on Chinese Restaurant Syndrome was actually published in the new England Journal of Medicine back in 1968 and the author was RH Quok. In his paper, he reported that after consumption of Chinese food, there was some reports of what he called Transient Subjective Symptoms. Which included some of the classic symptoms discussed in this episode.
To report this episode to you, I looked at quite a number of individual studies and they all unfortunately were reporting inconsistent results. So, that took me to the next step and that was to look at systematic review papers of the individual papers. So, the question that comes up is. Is MSG actually bad for you? According to the FDA and numerous scientific studies, it isn’t. however, there are people who consume food or liquids with MSG and report a number of different unpleasant symptoms. Including headache, flushing, nausea, chest pain, sweating, general weakness, pressure or tightness in facial muscles. As well as numbness, tingling and even burning sensations in the neck or the face.
Some people also report heart palpitations. Could all these people be wrong and the government be right? Is this a simple yes or no answer? Well, the Food & Drug Administration classifies MSG as gras. So, that’s an abbreviation. So, GRAS in capital letters and it means generally regarded as safe. MSG is not only used in Chinese food; it’s also used to enhance the flavor of soups and canned vegetables and canned meats and other things. It’s not just the FDA that says that MSG is safe, joint expert committees from the Food & Agricultural Organization of the united nations otherwise known as the FAO. And the expert committee on food additives of the World Health Organization otherwise known as the WHO or WHO.
They conducted studies on MSG in 1971, 74 and then again in 1987. They determined what they called an ADI or Accepted Daily Intake. And they concluded that the use of MSG did not present a health hazard. How can so many people have such a wide range of symptoms while the government says that MSG is safe? To answer a question like that, would require an exhaustive scientific study and that simply isn’t possible for me to either finance or conduct at this time. So, the most logical approach is to look into peer-reviewed science journals to find what’s called a meta-analysis or a systematic review paper.
Essentially a meta-analysis or a systematic review is simply kind of a study of a bunch of studies. Scientists conducting analyses of these type will study two or more studies to give a better consensus in most cases than simply looking at one study alone. This is definitely necessary when the question is about MSG. This type of analysis was conducted in 2016 by two researchers, named Obayashi and Nakamura. Their study was specifically designed to find out if there was a causal relationship with headaches reported by people using foods containing MSG. And if there was any scientific literature to support it.
These two scientists pointed out that MSG is classified as a causative agent of headache in the international classification of headache disorders third edition. The available scientific literature however gives us mixed messages. That’s what led me to look at a systematic review of a very large group of papers. Obayashi and Nakamura conducted this type of review on human studies, which included the incidence of headache after an oral administration of MSG. An analysis was made by separating human studies with MSG administration with or without food. This was done because different journals have reported inconsistent results based on the use of MSG in food or MSG in liquids.
MSG as an example is commonly used in Bouillon cubes and in soups. One of several individual studies that I looked at in preparation for this episode was by two scientists named Tarasoff and Kelly. This was a double-blind placebo control that was published in a peer-reviewed journal called Food & Chemical Toxicology back in 1993. Tarasoff and Kelly pointed out that conducting a blinded study was extremely difficult, because the taste of MSG was distinctive. And therefore, the placebo would be obvious to most test subjects versus a food or a liquid containing the MSG.
The idea of a double-blind placebo control study is that, no one in the study knows who’s taking the placebo and who’s taking the active agent. There have been other problems reported on individual studies to arrive at firm conclusions, this is not the only one. Once again this is why I looked at an exhaustive systematic review paper of a wide variety of studies. Tarasoff and Kelly reported that only 14% of the human test subjects in their study responded to the placebo and 15% responded to MSG. On the surface, this would suggest that there are almost as many people imagining that they’re having an effect as those who are actually reporting an effect from the MSG itself. So, this wasn’t very helpful.
Obayashi and Nakamura reviewed studies done on a very wide range of circumstances with various levels of dose administration of MSG. Some far above what you would normally get in food and in a variety of different foods and liquids. The results from one study to another were pretty inconsistent. Although, there was a suggestion that there might possibly be more significant effect on some females than males. Again, not conclusive. They acknowledge that doing a double blind with liquids was pretty difficult, in fact pretty close to impossible. Because you can taste the MSG and the liquids distinctly
After analyzing all of the data together their conclusion was that, there was no causal relationship that could be established between the intake of MSG and headaches. Now that’s after reviewing a very wide number of studies under a really broad scope of circumstances. Headaches are of course only one symptom that are reported by people who seem to be sensitive to MSG. So, it’s clear to see why government agencies tell us that MSG is safe. They’re going on the available science that’s been published. In science, you have those things which are proven, those things which are disproven and those things that require further study.
In the case of MSG, clearly further study is required. I have seen many people in my career who I believe sincerely are suffering the effects of MSG. But without the science to substantiate it, we can’t draw the conclusions that many people are looking for at this point. So, just because the study hasn’t been shown yet to validate a causal connection between these unpleasant symptoms and the MSG, that doesn’t mean they’re not real. I believe they are.
So. if you consume a food or a food additive and have any symptoms that are less than pleasant or positive. The prudent thing to do is to avoid that food or food additive in the future. I wish that for the purpose of this episode, I could give you absolute conclusions. But unfortunately, the science isn’t there yet. So, that’s it for this episode of The Nugent Report. Remember be safe, be sensible and stay objective.
Thanks for listening to this episode of The Nugent Report visit our website at ‘drnugent.com’. For more objective facts about health and nutrition and email your questions and feedback to info@nugent.com. Be sure to follow us on Facebook, Twitter and Instagram @TheNugentReport. Stay informed get the facts with The Nugent Report.
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《纽金特报告（The Nugent Report）》第4集：谷氨酸钠
《纽金特报告》，阐述健康与营养背后的科学。欢迎收听本集《纽金特报告》。《纽金特报告》是有关健康和营养客观信息的权威来源。由著名心理学家、作家、公共演说家、科学、健康、保健和营养方面的专家史蒂夫纽金特（Steve Nugent）博士主讲。我们的网站是“drnugent.com”，你可以在脸书（Facebook）、推特（Twitter）和Instagram @TheNugentReport上关注我们。
史蒂夫纽金特：大家好，欢迎收听新一集《纽金特报告》。在这集《纽金特报告》中，我们要讨论的是MSG（谷氨酸钠）。此前，我们在《纽金特报告》的脸书（Facebook）主页上进行了一项民意调查，大多数参与者表示他们希望听到关于谷氨酸钠的播客或看到写它的博客文章。好吧，虽然我本来没有计划做这个内容，但这是订阅者想要听的，所有就有了本集播客。如果你对谷氨酸钠很敏感，或者至少你相信自己很敏感，这说明你对什么是谷氨酸钠已经有了一定了解，但并不是每个人都是这样。所以，让我们先来解释一下什么是谷氨酸钠。
MSG是谷氨酸钠的缩写，通常在很多食品中作为增味剂。从肉汤块到罐头蔬菜中都有谷氨酸钠。有意思的是，谷氨酸钠最早是由一位日本科学家在1908年分离出来的。那时他正在研究一种在海藻中发现的特殊味道，这种海藻叫做昆布（Kombu），是一种可食用海藻。他成功提取出了谷氨酸钠。所以，其实谷氨酸钠已经存在很长时间了。从化学方面来看，它是谷氨酸的钠盐。谷氨酸是一种非必需氨基酸，也就是说，它天然存在于人体内，是体内构建蛋白质所必需的成份。谷氨酸存在于许多不同类型的动植物蛋白质中。
谷氨酸也是一种神经递质，所以说它相当重要，是氨代谢必需的物质。请注意，谷氨酸不是谷氨酸钠。经常有人问我这个问题，这两者不是同一种东西。谷氨酸钠是谷氨酸的钠盐。美国食品药物管理局（FDA）指出，谷氨酸钠是安全的，但有些人不同意这种说法。有些人甚至暗示，谷氨酸钠会导致脑损伤。我必须指出，没有任何经过同行评审的科学文献支持这一观点。请记住，《纽金特报告》致力于为你带来科学的客观事实。这意味着我们会带你全面了解相关事实。
通常将报告出现与谷氨酸钠有关各种症状的人说成是得了中餐馆综合征或CRS。因为烹制中餐时最常用到它。实际上第一篇关于中餐馆综合症的论文早在1968年就发表在《新英格兰医学杂志》上，作者是RH Quok。在他的论文中，他报告称，食用中餐后出现一些他称之为“短暂主观症状”的反应。其中包括本集中讨论的一些经典症状。
为了准备这一集内容，我翻阅了不少独立研究，遗憾的是，这些研究报告的结果都不一致。为此，我不得不进一步查看这些独立文献的系统综述。那么，问题来了，谷氨酸钠真的对人有害吗？根据美国食品与药物管理局和众多科学研究的结果，它无害。然而，有人食用含谷氨酸钠的食品或液体后，报告出现许多不同的不适症状。包括头痛、面红、恶心、胸痛、出汗、全身无力、面部肌肉压迫或肿胀。以及颈部或面部的麻木、刺痛甚至烧灼感。
有些人还报告出现心悸。难道这些人都错了，而政府是对的吗？这个问题可以简单地用是或不是来回答吗？美国食品药物管理局将谷氨酸钠归类为一般公认为安全（gras）。GRAS是它的缩写名称，全部大写，意思是一般公认为是安全的。谷氨酸钠不仅被用在中餐里，我们还用它来提鲜汤、罐头蔬菜、罐头肉类和其他食物的味道。不仅仅是美国食品药物管理局认为谷氨酸钠是安全的，联合国粮食及农业组织，也就是粮农组织的联合专家委员会，以及世界卫生组织也就是WHO的食品添加剂专家委员会，均认为谷氨酸钠是安全的。
他们分别在1971年、1974年和1987年对谷氨酸钠进行了研究，并确定了所谓的每日允许摄入量（ADI）。他们得出结论，使用谷氨酸钠不会对健康造成危害。为什么政府说谷氨酸钠是安全的，却还有那么多人出现广泛的症状呢？要回答这个问题，就需要进行详尽的科学研究，而无论是经费还是时间，对我来说根本不可能进行这样的详尽研究。所以，最合理的方法是在经同行评审的科学期刊中去寻找所谓的荟萃分析或系统综述。
本质上来说，荟萃分析或系统综述只是一种对数个研究所进行的研究。科学家在进行这类分析时，会研究两个或多个研究，以便在大多数情况下找出更好的共识，这类分析比仅看一篇研究更加可靠全面。而在涉及有关谷氨酸钠的问题上，这类分析绝对是必要的。关于谷氨酸钠的这类分析由名叫大林（Obayashi）和中村（Nakamura）的两位研究人员在2016年进行。他们设计了专门的研究，用来探究食用含谷氨酸钠食物人群报告的头痛与谷氨酸钠是否存在因果关系，以及结论是否有科学文献支持。
这两位科学家指出，《国际头痛疾病分类（第三版）》将谷氨酸钠归类为头痛病因。然而，现有的科学文献却提供了大量相互矛盾的信息。这就促使我仔细研究大量论文的系统综述。大林（Obayashi）和中村（Nakamura）就人体研究进行了系统综述，包括服用谷氨酸钠后头痛的发生率。将食用含谷氨酸钠食物和不含谷氨酸钠食物的人体研究分开分析。之所以这样做，是因为不同期刊根据食物中使用味精或液体中使用味精的情况，报告了不一致的结果。
以谷氨酸钠为例，它通常被用在肉汤块和汤中。在准备这一集内容的时候，我看了几篇独立研究，其中一篇是由名叫塔拉索夫（Tarasoff）和凯莉（Kelly）的两位科学家进行的。这是一项双盲安慰剂对照研究，早在1993年就发表在《食品与化学毒理学》这一同行评审期刊上。塔拉索夫（Tarasoff）和凯莉（Kelly）指出，由于谷氨酸钠的味道很特别，因此进行设盲研究非常困难。大多数受试者很容易分辨出安慰剂与含有谷氨酸钠的食物或液体。
双盲安慰剂对照研究的设计思路是，研究中没有人知道谁在服用安慰剂，也没人知道谁在服用活性物质。得出肯定结论的独立研究还报告了其他问题，设盲不是唯一的问题。这就是为什么我要看一份详尽涵盖各种研究的系统综述论文的原因。塔拉索夫（Tarasoff）和凯莉（Kelly）报告说，在他们的研究中，只有14%的受试者对安慰剂有反应，而15%对谷氨酸钠有反应。从表面上看，这一数据表明想象自己受到谷氨酸钠影响与实际报告受到谷氨酸钠影响的人数一样多。所以，这一结论不是很有帮助。
大林（Obayashi）和中村（Nakamura）的回顾研究范围非常广，包含食用各种剂量水平的谷氨酸钠，有些剂量远远高于通常从食物或从各种不同食物和液体中所能获得的水平。各项研究中的结果相当不一致。虽然有人推论，谷氨酸钠对某些女性可能会比对男性有更显著的影响。但同样，没有确凿的证据可以证实这一点。他们承认用液体做双盲研究是相当困难的，事实上几乎是不可能的。因为你可以轻易区别出含谷氨酸钠的液体。
在分析了所有数据之后，他们得出结论，在摄入谷氨酸钠和头痛之间不能建立因果关系。这是在回顾了非常多的研究，覆盖面很广的情况下得出的结论。头痛似乎只是对谷氨酸钠很敏感的人所报告的一种症状。这样就很清楚的解释了为什么政府机构告诉我们谷氨酸钠是安全的。他们依据的是已经发表的现有科学成果。在科学领域中，有些结论被证实，另一些结论被否定，还有一些结论需要进一步的深入研究。
对于谷氨酸钠，显然需要对它进行进一步的深入研究。在我的职业生涯中，我见过很多人，我真心相信他们受到谷氨酸钠的影响。但是，如果没有科学证据，我们现在还不能得出这个很多人情愿相信的结论。不能仅仅因为研究还没有证明这些不愉快的症状和谷氨酸钠之间存在因果关系，就认为它们不是真的。我相信它们是真实存在的。
所以，如果你食用了某种食品或食品添加剂，出现了任何不愉快或阳性症状。谨慎的做法是以后要避免食用这种食品或食品添加剂。我也希望自己可以在本集中给各位一个确凿的结论。但遗憾的是，相关科学研究还不完善。这就是本集《纽金特报告》的全部内容。请记住要安全、理智、保持客观。
感谢收听本集《纽金特报告》。如需了解更多关于健康和营养的客观事实，请访问我们的网站’drnugent.com’。请将你的问题和反馈发送至info@nugent.com。请在脸书（Facebook）、推特（Twitter）和Instagram @TheNugentReport上关注我们。《纽金特报告》，带给你最新信息，让你获取客观事实。