Welcome back to the Bite Me podcast. Today, I wanted to have a bit of a chat about a fun little thing called monosodium L-glutamate, which is understandably more commonly referred to as MSG. It's found in a huge range of foods all throughout the world. It's very, very commonly consumed.

And so it's important that we have a bit of a chat about it because there's also a fair number of claims around its impact, particularly its potential negative impact on our health. And so I wanted to dive into some of those claims, explain the background and give you a good understanding of what is important to understand, and what is important to ignore.

So, basically, it's the combination of sodium and something called glutamate, which is the most, I'm pretty sure it's the most common amino acid found in protein-containing foods.

So remember that a protein is made up of lots and lots of different amino acids. And so our protein-containing foods, the most common amino acid that you're going to find in those foods is glutamate. Okay?

So one of the biggest components of MSG is already something that we're getting exposed to very, very commonly if you eat protein, which we all eat. We should all be eating protein.

So MSG though, when we combine these things, it really provides the strong umami flavor, which is one of the five flavors kind of giving it this, I don't know, deep, savory-style flavor versus, say, sweet or bitter or sour.

And so it does... MSG does occur naturally in a heap of foods. It's not just the white dodgy-looking powder that you might see added in the scary YouTube videos. It occurs naturally in things like Parmesan and Vegemite, oyster, soy sauce, mushrooms, tomato. And so, again, we're going to be exposed to it naturally.

Anyway, now, of course, the issues or the claims come when we're talking about sort of high doses of these things or kind of concentrated artificially created MSG that's being added to foods to make them tastier.

So just to put some numbers around it, in terms of a typical intake of MSG in Western countries, the average intake of MSG is about 0.3 to 2 grams of MSG a day. Okay. That average is a bit higher in Eastern countries, mostly just from the dishes that they would typically consume culturally. And that's, you're looking more like a 1.5 to 3 grams per day.

Those numbers are important. We will be coming back to those because it's, again, when we're getting into some of these claims, it's always important to put those claims in context with what people are actually doing. So, Western countries, 0.3 to 2 grams, Eastern countries, 1.5 to 2.5 to 3 grams of MSG a day.

It's also really important that we understand how glutamate, in particular, but MSG is metabolized and digested and absorbed in the human body. Glutamate, again, because we are exposed to so much of it is very, very, very rapidly metabolized and digested in the small intestine.

So it's really rare that anything gets past that. If you've got a really bigger dose, bigger, a much larger dose of MSG, some might get metabolized by the liver. But ultimately nothing makes it out of there, right? That's kind of where it's all broken down and it's all will start to disperse around the body. And so it's really important that we only really pay attention to studies where people are orally consuming MSG.

A lot of the studies where you see problems, A, in animals which is what we'll come to. But B, they injected with it, which means it goes directly into the bloodstream and it completely skips the gastrointestinal system. It completely skips your stomach, your small intestine, your large intestine.

And, again, that's where most of, if not all of the MSG will get broken down. So it's not even really a fair comparison to just dump it into the blood and then start to talk about all the terrible things that happened because when you can orally consume MSG, typically won't make it into the blood as MSG.

So remembering that, the second thing is most of these studies are done in mice. Okay. So first, they go the intravenous route with MSG rather than the oral route. And secondly, mice actually metabolize MSG quite differently to primates which we are. And so using them as a proxy for MSG metabolism is not a great idea.

We see their blood levels rise differently when they consume the MSG. So if they are given the MSG orally, a lot more MSG does make it into the bloodstream because their gastrointestinal system doesn't digest and absorb as effectively as ours does.

And secondly, as well, we need to talk about something called the blood-brain barrier, which sounds pretty metal when I say it like that. But essentially, the blood-brain barrier is kind of this barrier of cells that we've got surrounding our brain.

Hopefully, its purpose, if it's working properly, is to act as a bit of a buffer between the things that are circulating in our blood and it only allows "good things" to transport across this blood-brain barrier into our brain. So it's a really solid line of protection. And only certain things can get across this blood-brain barrier.

Our blood-brain barrier is quite different to rodent blood-brain barriers. I need to call that something else. The BBB, no, that's terrible. I'm going to keep saying blood-brain barrier.

A rodent blood-brain barrier does not protect against the MSG, which can be a problem. It often means that more glutamate gets absorbed into the brain. Glutamate can impact and almost overexcite the nerves in the brain and can lead to brain damage, brain lesions.

And that's definitely something you're going to come across in studies. They're going to be talking about these high doses of MSG causing brain lesions. Brain lesions are super serious. That's absolutely something we want to avoid.

But we need to remember we're talking about a mouse that has been injected with MSG. Not only that. They're typically injected with bat poo crazy levels of MSG. In one study, they were given the equivalent of 500 mg/kg of MSG.

So for me, that's about 45 grams of MSG. Remembering that the average Eastern intake, so our population that consumes it even more consistently, is three grams a day. I don't even think that's comparable.

On top of that, pretty much the largest palatable dose that you're going to find in humans is under 60 mg/kg of body weight. We find that if people consume over that with MSG, they start to feel sick. They've got nausea and potentially vomit.

So the likelihood of you being able to consume that level, that study is referring to in mice is, well, basically impossible. And then we're also remembering that we're consuming it. We're taking it orally. We're allowing our gastrointestinal system a chance to break it down. We're also almost certainly consuming it with food.

And there's a number of studies that show, if you combine or if you consume MSG as part of a meal, that dramatically changes its impact in its metabolism. Okay. It slows it down and it allows you to break down all that really simply and really effectively.

So, in summary, brain lesions, which again, terrifying phrase. You see an article that says, MSG will give you brain lesions. I am clicking on that, but what they are not saying is give mice the most insane level of MSG possible. Don't let them eat it, inject it into their blood.

Mice with different blood-brain barriers, mice with different biochemistry to us, and, hey, they get brain lesion. Like, that sucks, but that's probably not very relevant to my consumption of MSG at all.

So from a safety perspective, and, again, given the fact that MSG is consumed so commonly in foods, there's been a number, a huge number of studies and reports done investigating the safety of MSG. And they haven't found anything that we should be concerned about.

In terms of a few more "minor" things, the other two things that you often hear about are its impact on weight gain or inability to lose weight. And there's kind of two theories that are hypothesized here.

The first is, and this one kind of makes sense in my mind, it makes food tastier. So you're probably going to eat more. There's also another hypothesis that talks about potentially directly impacting the areas of the brain that regulate body mass. And kind of change your metabolic rate, make it difficult in the future to lose weight and things like that.

The thing is those are theories. I don't really play out in the studies that we can see. Okay. There is some observational data in humans. I think there was a meta-analysis that had five observational studies in it. And I think two showed a potential link and three showed no link.

It's really important in observational studies that we remember they can't prove what we call causality, which means they can't prove that thing A has caused thing B. All they can do is show that thing A and thing B might be related, but there might be lots of other things going on.

And there is a lot of talk around the fact that higher intakes of MSG in these populations typically also result... They're consuming higher fatty animal products. They're more sedentary. There's more alcohol. There's more smoking. There's more all of these other behaviors, which aren't great for health or body mass either.

So, in a couple of studies that have actually tested, they've sort of done clinical trials of MSG. They haven't really found that groups that have consumed more MSG have gained, have eaten more calories.

Now this isn't a long 10-year trial, but it is a really good way of looking at that because it looks at the way that people would normally consume MSG. It looks that free-living people consuming food with their MSG allowed to eat as much as they want. And it appears that it has no impact on what they consume.

So again, that study's more relevant for me. That makes a lot more sense. I can't see that there's any real strong evidence showing that MSG is going to negatively impact someone's body mass.The last area you might commonly hear people talk about is intolerance or sensitivity towards MSG. It's actually, it's been given a name called the Chinese restaurant syndrome.

To sum up all of the studies that have been done in this, studies that have been performed correctly, and that is as a double blind, placebo-controlled trial in humans combined with food. So those are all the things that I care about.

Things that are important, double blind, meaning the participants and the people running the studies didn't know who was getting MSG. And who wasn't, and a placebo-controlled trial means that there was a group that was given a placebo, so no MSG and a group that was given MSG. So we can make comparisons there.

And like I said, it was in humans and humans eating food plus MSG, really applicable, really helpful in that they found a zero correlation. They found people who thought they were sensitive to MSG were able to consume MSG with no symptoms because they didn't know they were consuming MSG.

So, hopefully, that's answered a few of your questions around MSG's safety, whether it's going to affect body mass intolerances cause brain lesions. I can't even say brain lesions without shuttering, and giving you a bit more confidence and understanding of what the actual facts around MSG.

Finally, I'll also put a link on the website in the show notes at the top. I'll make it the first one, a really good report. It's quite simple, very, very easy to digest and understand. No pun intended. That kind of also simplifies all of the things that I've talked about today.

So, hopefully, you have found this beneficial. If you have, as always, please leave a review, rate, subscribe, send me a carrier pigeon, put a photo of the thing, the screenshot of the thing, the episode up in your Instagram stories, and tag me so I can say thank you. And I'll see you next time.