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

**Peter Attia** (0:11)
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 peterattiamd.com forward slash 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? 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 100th episode, did a special AMA that was titled Something Along the Lines of Strong Convictions Loosely Held or High Convictions Loosely Held.

**Matthew Walker** (2:14)
Strong Beliefs Loosely Held.

**Peter Attia** (2:15)
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.

**Matthew Walker** (3:04)
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.

**Peter Attia** (3:43)
So it's either getting stronger, more nuanced, or you're moving towards rejecting.

**Matthew Walker** (3:48)
Correct, yeah. So I'm now trying to think of examples in maybe all of those three.

**Peter Attia** (3:53)
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.