#127 - AMA #3 with sleep expert, Matthew Walker, Ph.D.: Fasting, gut health, blue light, caffeine, REM sleep, and more

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Hey everyone, welcome to a Sneak Peek, Ask Me Anything or AMA episode of the Drive Podcast. I'm your host Peter Attia. At the end of this short episode, I'll explain how you can access the AMA episodes in full, along with a ton of other membership benefits we've created. Or you can learn more now by going to Peteratti md.com subscribe so without further delay, here's today's sneak peek of the Ask Me Anything episode.

Welcome to a special follow up Ask Me Anything interview with my guest Matthew Walker. This is part of a two part interview, the first part being last week. In this AMA episode, Matthew and I discuss the following what has Matthew changed his mind on? Or what does he now believe to be true or untrue based on emerging evidence? Evidence. And in particular he brings up topics around blue light, caffeine, REM sleep, and sleep wearables. We also dive a little bit into the topic of sleep and electromagnetic force. We discuss how fasting can impact sleep. We talk about restless leg syndrome or rls, talk about magnesium in particular as a sleep aid, talk about how sleep can impact the gut. And we end with an interesting conversation around what Matthew believes is the next step function evolution when it comes to sleep.

Just as a quick reminder of Matt's.

Credentials, he's a professor at UC Berkeley in the departments of Neuroscience and Psychology and he's the founding director for the center of Human Sleep Science. He's trained in the UK and he is the author of the international bestseller why We Sleep. So without further delay, please enjoy this special AMA with Matthew Walker.

So Matt, I don't know, a few months ago Bob Kaplan and I, I think it was actually for our hundredth episode, did a special AMA that was titled something along the lines of Strong Convictions Loosely Held or High Convictions Loosely Held.

Strong Beliefs Loosely held.

Yeah, strong beliefs Loosely held. All basically a flavor of the same theme, which is what are things that you believe with great conviction but you're willing to hold them loosely enough and in the presence of new information you've changed your mind. And I get asked this question a lot. In fact, I find it one of the most enjoyable questions people ask me, which is, Peter, what do you believe today that you did not believe five years ago? And conversely, what did you believe five years ago that you categorically do not believe today? So let's start with either of those. Take either one. Or feel free to not even separate them.

But basically, where is your belief system today? Matt Discordant from where it was.

I don't know, four or five years ago, when you were, say, in the throes of writing your book, which is probably the most you thought about this problem?

The way I think about this as a scientist, not from this question perspective, but I usually have sort of three buckets in my mind, evidence that's coming in that's helping reinforce a belief that I have. So I'm more bullish things that I believed that now the evidence has added to, which means that I haven't changed my mind on the original belief, but I've had to add a new construct in that equation of the belief. And then the third one is contradiction. Where I've got now evidence against that hypothesis that I once believed there was evidence to support it, and now I'm rejecting that hypothesis.

So it's either getting stronger, more nuanced, or you're moving towards rejecting.

Correct? Yeah. So I'm now trying to think of examples in maybe all of those three.

While you're thinking of that, Matt, can I just give you a minute to think about that? But also an opportunity to go on. One of my favorite rants about science, which is sort of a pet peeve of mine, is the way that science has been represented in the press as anything but probabilistic. And one of the problems with the world we live in is most people don't have the opportunity to be educated scientifically and therefore they especially in a manner where it's experimental. Not that there's anything wrong with disciplines of science that don't have as much experimentation, but if you're privileged enough to get to cut your teeth a little bit in an experimental discipline of science, you start to realize that it's really all probabilistic. I mean, data are very messy. And therefore the best you can do when an experiment or many experiments are concluded is increase your confidence in the probability of something being true or being false. And I remember a mentor of mine once explaining that because I had a background in mathematics, he said, look, you just have to get used to the fact that there's no proving anything in science. Your last proof was done when you left the faculty in mathematics. You are now going to spend the rest of your life looking at high, high, very high, low intermediate probability events. But the days of this is proved or this is disproved are really over. And so one, I hope that little soliloquy is helpful for folks to understand how it is that in science you can walk back from things you believed or add nuance to things you believe or walk forward on things. And hopefully, if you could drone out my voice as I said that, Matt, it also gave you time to think of that because I know it's a tough question to get asked.

I didn't tune out. I love what you're saying. I'm very actually envious of mathematicians because I think it is the only deterministic discipline where you. If once a proof is a proof, it's a proof for the most part, forever. Whereas with science, all we ever really do is hopefully disprove what we think it isn't. And we're never certain about what it is, but we're getting a little bit more certain, hopefully, or less certain. But we can never prove anything like a one or a zero with mathematics. So with that said, it's not necessarily that hard of a question because I'm constantly trying to run these calculations about all of my scientific sleep beliefs and think about these three buckets. I think the thing that I've probably changed my mind on most or had a reversal on is the effects of blue light on our sleep. And in fact, in the book, I spoke about a study at the time that had been done out of Harvard, which I still think is valid, where they'd used an iPad where you read on an iPad for an hour versus you read a book under dim light. And they showed that that iPad had this detrimental effect on sleep. It had delayed the release of melatonin, it had caused a reduction in REM sleep, and even when they stopped reading the iPad, it had a blast radius to it where the sleep quality was still bad for a couple of days afterwards. And it was a compelling study and published in a good journal. But over the years, I think there's been some research that's pushed back on that and there's been some great work from a university in Australia called Flinders University. And Michael Gradizar has done some just great work on this at Flinders. He has changed my mind. I'm less bullish now about the idea that these devices that we use are sleep disruptive because of the blue light. I still think that has an effect. But what I think he's shown in some elegant work is that it's less about the light. It's more about the fact that these devices are just so activating, that these devices are designed to trigger alertness and what we call physiological arousal in the brain. And in other words, what happens when we use these devices, the reason that they're so disruptive to our sleep is less about their blue light. It's more the fact that we are masking our sleepiness with this overriding artificial activation from the devices. In other words, let's say that all of a sudden it's 10pm and you think, I'm wide awake, I'm on my computer, I'm working, I've got my phone next to me, I'm checking it, it's pinging, it's dinging. All of a sudden all of the lights go out. There's a massive electromagnetic pulse that curses across your environment. It knocks out all of the devices. You've got no phone, no iPad, no electricity. I suspect that within about 15 or 20 minutes you'd start to feel sleepy. And it's not because of the blue light effects, it's the fact that you are, and you were all along sleepy. But these devices, because they're so activating, was creating a competing force that hit the mute button on the sleepiness and it activated you. So I've actually down regulated my belief in the effects of blue light and I've introduced this new mental framework regarding the effects of the invasion of technology into our evening lives and our bedrooms. And I'm much more now enamored with this idea that they are mentally stimulating rather than blue light emitting.

Forgive my ignorance for this question, but has the experiment not been done where you've taken groups of subjects and you've subjected one group to just a blue light? So an actual blue light that's hitting, I forget how many nanometers that is, but the actual.

Right, in the short of that wavelength?

Yeah, yeah. And then you have another group that is just being blasted with red light, and then you have another group that is just being blasted with a regular LED and white light. So you're getting the same intensity of light, but you're moving the wavelength and therefore you're nullifying the stimulatory effect of what's being read or looked at. I mean, to me, that experiment would eloquently demonstrate whether or not blue light per se is the problem. Has that not been done?

It has. So people have played around with the wavelength of the light. And what we believed is that it's the cooler blues, the shorter wavelength light that are most detrimental. And the reason that screens were blamed is because they are LED based, which is enriched in the lower visible light spectrum, the shorter wavelength, in other words, the cool blues. And that's why the blame came, because it was stamping the brakes on melatonin especially powerfully. And those studies were done. They were done by Chuck Seisler and Steve Lockley. From Harvard years ago and that led to this sort of belief. And I still think there's good validity in that. And by the way, there was a couple of studies that came out in animals that were now suggesting, at least I think it was in rats or mice, I could be wrong. Or if it was in fruit flies, I apologize, where they actually found the opposite, where they found that the warmer color lights had stronger blocking effects on melatonin. It began this sort of controversy had we got it wrong about blue light. And then this work from Flinders University from Michael was coming online regarding this cognitive component. And it really sort of made me shift my belief system. So yes, those studies have been done and they principally looked at melatonin. I think they studied less a full night of sleep with polysomnography and really asked the downstream consequences. They were just simply saying, how does it affect your melatonin? Which is maybe one step short of saying how does it then affect, as a consequence of that change in melatonin, your subsequent sleep? Without necessarily doing a much more sophisticated study, which I think are now being done, where you do the Coke Pepsi challenge of same amount of light stimulation. So light is standardized, right?

Light becomes the variable. That's the only independent variable.

That's right.

And then you start measuring independent variable at polysun and melatonin, for what it's worth and do everything.

And then you do a second round of studies where light actually becomes the constant stimulus where you maintain the same light exposure but in one condition. You're doing something cognitively activating like building a Facebook account or checking that versus you're simply just there in front of the blue light. But there's no cognitive stimulation to really do the two by two disambiguation of that. I think those studies are coming, but that's one of the things where I've definitely changed my mind, I think, and I felt compelled to now speak more about that and less about the blue light. The other place where I think I've changed my mind and maybe even some of my behavior is around coffee and caffeine.

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