When to Eat — The Optimal Schedule for Metabolic Health
Episode Stats
Summary
Emily Manoogian is a chronobiologist and clinical researcher at the Salk Institute for Biological Studies. She explains how to align your eating schedule with your circadian rhythm, including when to start eating after waking, when to stop eating before bed, and what happens to your metabolism when you don t follow these timing guidelines.
Transcript
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Brett McKay here, and welcome to another edition of the Art of Manliness podcast.
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When it comes to weight management and all-around good metabolic health,
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Well, my guests would say that it's also a crucial thing about when to eat.
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Emily Manoogian is a chronobiologist and clinical researcher
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Today on the show, Emily shares how to create an optimal schedule
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for a healthy metabolism by aligning your eating schedule with your circadian rhythm.
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She explains when to start eating after waking,
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and what happens to your metabolism when you don't follow these timing guidelines.
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We also talk about how to best distribute your calorie intake throughout the day
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and how to eat to mitigate the metabolic problems that come with being a shift worker.
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After the show is over, check out our show notes at aom.is slash whentoeat.
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All right, Emily Manoogian, welcome to the show.
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You research all the rhythms that happen in our body from sunup to sundown
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and then in between, too, while we're sleeping.
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And what led you to focus on the intersection between our circadian rhythm and eating?
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Yeah, so this started quite a while ago when I was an undergrad in college,
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and I actually took a class called Hormones and Behavior
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with Lance Kriegsfeld at UC Berkeley, and I was instantly enamored.
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I was just fascinated with the subject that all of these rhythms control everything within our body,
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and that wasn't even the biological rhythms class,
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but it started to touch on rhythms because of seasonal reproduction in animals.
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And I fell in love with it so much, I bothered him until he let me into his lab.
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I took his next course on biological rhythms, and I was kind of hooked.
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So then I did my PhD in neuroscience and behavior with Eric Bittman out in UMass Amherst,
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but I really got into hardcore circadian biology at that point,
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trying to understand this mutant hamster that could like phase shift 12 hours over a night,
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like think like you could go to India and have no jet lag.
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And so I was trying to understand how this worked.
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And, you know, it always comes back to the molecular clock, which was really kind of cool.
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But in that time, I realized I really wanted to use my knowledge of circadian rhythms to kind of
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apply it to humans and to help other individuals,
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because the only reason I knew all about this was because I was taking these very specific courses,
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And so I had this amazing opportunity to come to the Salk Institute to work with Sachin Panda,
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who mainly does wet lab and kind of basic science,
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but had gotten into time-restricted eating through rodent studies,
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It just done one study kind of as a pilot and brought me on to get into this whole new field
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and really kind of understand how timing of eating affects human performance and human health.
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A while back ago, we had circadian researcher Russell Foster on the podcast to discuss circadian rhythms,
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but something we didn't dig much into is the relationship between circadian rhythms and our metabolism.
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And I want to make that the focus of our conversation, because it's just really fascinating.
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Can you walk us through the metabolic changes our body goes through during a 24-hour period?
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And caveat to this is, you know, when you're talking about metabolism,
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it's not like you're only talking about the stomach or the gut or, you know,
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it's your whole body works on metabolizing things.
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I mean, you could think of muscle as your biggest kind of metabolic organ in a lot of ways.
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And the circadian system controls pretty much every organ in your body.
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So when you're sleeping, your body's trying to, hopefully you're fasting as well.
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So when you're sleeping, hopefully you're fasting and your body's actually able to break down fats
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that you've built up over time or during the day and release glucose into your body.
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Because if you're fasting at night, you're not taking in new sugars and your body and your brain
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And so you need some glucose in your body and going through your blood.
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Glucagon is released to try to get that back into your blood.
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When you wake up, you actually have this little spike in cortisol just before you wake up.
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And that kind of helps your body wake up for the day.
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You also get your sharpest rise in blood pressure.
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And for some people, this can also, you'll also see like a little increase in glucose
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in the blood just from getting up and starting to walk around because your muscles need that
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So sometimes it can rise just a little bit because of that.
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And your circadian rhythms have also organized, you know, worked with your liver to create enzymes
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So you're actually very able to break down food and digest a high amount of calories in
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So we generally think kind of like an hour or two, maybe three after you've woken up is
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probably the best time to be able to process a big meal without having giant glucose spikes
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or any other kind of negative consequences because your body's really up and moving.
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And then throughout the day, while you're active, your body is still very able to digest a lot
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of calories, a lot of different types of macronutrients.
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And that's really kind of when you should be eating is when you're active.
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As you get later in the day, you know, again, having your last meal in the early evening or
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even, you know, not too late into the night where you're getting too close to bed is not
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But the issue becomes is when people don't eat much during the day and then eat this huge
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meals at night and you're really not able to process these really huge meals at night
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or very late at night because your body's starting to get ready for rest, meaning it's
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not producing all the enzymes you would need to break everything down.
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It's not going to be able to use up all those calories you just ate.
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And a lot of times after dinner, people are sitting down, you know, they're not really
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And when that happens, that becomes a little bit of a problem for it just kind of staying
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And then you're not going to get to break down those fats at night.
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The other thing that's happening at night is melatonin starts to get secreted and melatonin
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It also is regulated by the circadian system and melatonin helps you fall asleep.
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It also helps coordinate your metabolism by suppressing insulin secretion.
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So if you're eating really late at night when your body is tired and it's dark, you don't
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have insulin in your blood to be able to take that glucose out of your blood and pack it
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And so this is why when you eat a lot right before you go to bed, your glucose levels will
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actually go really high and stay high sometimes for many hours.
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And that will completely inhibit any fat breakdown or anything like that.
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So depending on when you eat will kind of change what your body's doing at different times
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But if you consolidate your food to your active phase, then you can kind of fast and break
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down fats at night and use up a lot of the fuel you're taking in during the day.
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So when we're asleep, our body primarily uses, it's breaking down fat.
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There's a process where your body can turn fat into glucose.
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But I also know that our body stores glucose in our liver.
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Does our body use that glucose supply when we're asleep?
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Yeah, so you can release glucose from your liver.
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And one of the problems with getting too much glucose or having highly high levels or not
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being able to break things down is over time, you can also get fatty liver disease.
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And this is really tricky because we know it's a common problem, but it's not very often assessed
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just because the testing for this is quite invasive.
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And there's not really much you can do about it aside from healthier diet and also, I would
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But research is going on to really determine how effective that is.
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But you can get this fatty liver disease where if you don't use up a lot of these sugars that
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are in your liver, you can develop fat deposits within the liver.
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And over time, that makes it so the liver doesn't function properly.
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I know some people, particularly with like their pre-diabetic, when they wake up or even
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like before they wake up, they have like a huge glucose spike.
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Like it can like be 120 when they hadn't eaten anything in hours.
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What's going on with the metabolism to cause that?
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So when you get into things like pre-diabetes or type 2 diabetes, you know, it's not a normal
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It's not like it's just higher levels of the same system.
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That means that the glucose regulation is compromised and there's not one way that it
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In type 2, there's many different subcategories and there's different mechanisms for why that's
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So depending on the individual, I could give you a different answer.
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But you do see this in some individuals where when they first wake up, especially sometimes
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when they go for a walk, they all see this big jump.
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And I've seen this in individuals with, you know, women with gestational diabetes, sometimes
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like they were taking their finger pricks and they would go for a walk first and that
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And part of that is, you know, your muscles and stuff do need glucose.
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And so you do naturally get a small amount of glucose increase by just, you know, getting
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But in those individuals, it's kind of the system's over responding.
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And this is where you have some type of insulin resistance or you have some type of other issue
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going on that's causing the glucose regulation to be maladaptive.
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So when we're waking up, we have an initial glucose spike.
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If you're healthy, it's not going to be huge, but it's just enough to get your body going.
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And then the circadian rhythm is also going to start to bring on the insulin system.
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So, you know, insulin might not be ready for you to eat, you know, pancakes and syrup right
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It might take an hour or two before your pancreas is really pumping insulin out so you can start
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And part of that is melatonin suppressing insulin, right?
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So melatonin, we think of it at night, but it peaks like in the middle of your night.
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So things like getting a lot of really bright light in the morning and letting your body wake
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up for like an hour, that melatonin will then, you know, have plenty of time to shut
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Your body is ready to eat, which is why we usually recommend waiting at least an hour
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So your body is able to process that because people think about late night eating being
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And I think you see that more in individuals that might have a really early commute and have
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You know, I see teachers doing this a lot where they're like, well, I got to eat breakfast,
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but they end up eating breakfast like in the dark at like five in the morning.
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So we still have some melatonin in our system when we first wake up and that suppresses
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And then as the day progresses, your metabolism is turned on and you start releasing insulin.
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And then as we get closer to night, melatonin is increasing again, which tells insulin production,
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And then you're going back through that sleep process.
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So how can we put these pieces together and use this information of how our circadian rhythm
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manages our metabolism to optimize metabolic health?
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So, I mean, when it comes down to it, it's kind of obvious things when you think about
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It's allowing your body to fast at night and really eating when you're active.
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And that sounds extremely simplified, but that's kind of what the answer is, right?
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So we study a dietary intervention known as time-restricted eating.
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Some people consider it a form of intermittent fasting.
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Unlike other forms of intermittent fasting, it doesn't require any type of caloric restriction.
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It can be combined with it, but it's not required for it.
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And really it's just eating at the same eating window.
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So for example, 9am to 7pm, but it should be customized to your schedule.
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So someone who wakes up at 6am every day is going to have a different eating window than
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It should be adjusted to fit your schedule and it should be the same eating window every
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And the way we'd say to usually figure that out is think about what your normal sleep
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Hopefully you're at least trying to sleep for eight hours a day.
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You know, a lot of us don't get that, but that should at least be the goal.
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And then say, wait at least one hour after you wake up and stop eating at least three hours
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That gives you now a 12 hour window and then pick the 10 hours that work for you.
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And usually that's decided by a family meal and kind of working backwards that way.
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And just that simple thing of saying, I'm going to eat at the same times.
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I'm going to give that cue to my circadian rhythms that when I eat, I'm telling all the
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clocks within my body, what time it is just through nutrient availability and the stimulation
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But now you're saying, okay, here's a regular cue.
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And then the really cool thing about the circadian system is that it's anticipatory.
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It's not a reactive, like you ate and so now I'm going to do something.
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It's, I know you usually eat at this time, so I'm going to prepare enzymes to be able
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And so if you eat at regular times, your body will be more prepared to break down food at
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And then getting a regular fast that's long enough for your body, you know, at least like
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I mean, most of that's while you're asleep, but getting that daily fast is super important.
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So you can actually break down fats and use up sugars.
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So you're not creating this, you know, overload of resources that your body can't handle.
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Yeah, that sounds about what I do with my schedule.
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So I wake up at 5.30 and then I don't eat until seven and then eat during the day.
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And then our dinner is usually around 6, 6.30 and then nothing after that before I go to bed.
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You know, I mean, that's like what, 11, 11 and a half hours.
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But even with that, I don't think it's hurting you in any way.
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You're getting, you know, at least probably a three hour chunk before you go to bed.
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Like, I think that's a very reasonable way to eat.
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And you're aligning that with all the other cues that you're giving your body,
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like light and activity and social interaction and stress and exercise.
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Like all those other things are aligning so your body actually knows what time it is.
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And just the simple act of supporting your circadian rhythms is super helpful for almost
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Okay, so you want to have your first meal at least an hour after you wake up and then
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stop eating three to four hours before you go to bed.
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So you're aiming for an eight to 10 hour eating window overall.
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And what this does, it ensures you're eating when your metabolism is most active and then
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And also the other takeaway too is you want to eat at the same consistent times every day
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because that helps your body be prepared to process food.
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So you mentioned that there are some people who don't stick to the sort of time restricted
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What happens to our metabolism whenever we eat too soon after waking up and then eat
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Yeah, so part of this gets back to melatonin again, right?
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When you eat too soon, you just might not have insulin enough in your system where your glucose
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This is also a more common problem in the United States because a lot of our breakfast and not
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just the United States, but it tends to be a bigger issue here.
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A lot of the Western breakfast is very carb heavy.
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And there's also been some really interesting science into like food desires at different
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And the things that we crave when we're tired, like late at night or early morning are not
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We do not crave a salad or, you know, like just avocados in the morning.
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We crave a donut or a sugary coffee or something to give ourselves a treat because we had to wake
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So we try to treat ourselves with these really unhealthy foods.
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And at those really late times, we're specifically not able to eat, you know, process them properly.
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So eating super early in the morning, again, you're just going to have higher glucose response.
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When you're eating really late at night, you get that same kind of thing.
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What's really interesting though, and some really beautiful science has come out in the
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past couple of years for multiple groups now, but Frank Scheer's group at Harvard did
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this really nice study where they had participants in the lab and they provided meals to them.
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And they'd either give them dinner at 7 p.m. or to another set of participants, they would
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But the participants that got it really late not only had a higher glucose response, but they
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stayed to have elevated glucose responses for hours later into the night.
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And what was really interesting is even though they eventually got back down to normal fasting
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glucose levels, but the next morning they gave them a glucose tolerance test and the ones who had
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eaten the night before later, they didn't respond to glucose as well the next morning either.
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They had a higher response to it and it stayed elevated longer.
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And there's some nice work from Australia that came out also recently doing this in-lab model
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of shift work where they had people do simulated night shifts and either eat a large meal, a
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small meal, or nothing during the night while they were working.
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And even though they were active, that eating during the night led to compromise glucose the
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next morning in both groups that had any kind of food, but it was worse in the larger meal.
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So it seems like eating really late at night compromises both the glucose at that time and
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while you're sleeping, which can also cause you to have a worse quality of sleep, which
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But it also compromises your glucose the next day and potentially for multiple days after.
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So it really does seem to be throwing off the system in a pretty significant manner.
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And this constant disruption to glucose regulation, constant levels of higher glucose, I mean,
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that leads to pre-diabetes and type 2 diabetes.
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And it sounds like too, if you're managing pre-diabetes or type 2 diabetes, you have to
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think maybe what this research suggests is not only think about the type of foods you're
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eating, but like when you eat them can have a big influence as well.
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I've seen firsthand how timing your food intake can change how your body responds to it.
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So a while back ago, I tried out the continuous glucose monitor.
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I don't have pre-diabetes or anything, but I wanted to try it out.
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And something I saw was when I was doing it, my first meal would be very carb heavy.
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It's like a bowl of oatmeal and some yogurt and some blueberries.
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And my glucose would just spike and it would stay spiked for like a really long period of
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So something I did is I swapped to a kind of a lower carb meal.
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So it was just like eggs, some, yeah, it's just basically eggs and like a low carb wrap.
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And I moved my oatmeal later in the morning and then like, yeah, the carb spike went away.
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And then after I had my oatmeal later in the morning, I didn't have the same sort of spike
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as I had when I ate it first thing in the morning.
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And you know, the really great thing about continuous glucose monitors, or I'm probably
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And so they're also called CGMs is they tell you so much about how you specifically like
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you as a person respond to different foods because it's different for different people.
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And just like you said, the same food can cause a different reaction at different times
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And being able to wear a continuous glucose monitor is really powerful because you can
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You might learn like, just like you said, you can eat oatmeal, just not first thing.
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Or that same might be true for a donut, or maybe you can't have it early, or maybe you
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can't have it late, but in the afternoon, maybe it's not as bad for your system, you
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know, or people find out like, maybe they really have big spikes in response to rice.
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And you might have someone else eating the exact same meal that doesn't have that same
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There's individual differences between people, but usually people have something that gets them,
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whether it's rice or pizza or donuts or oatmeal or whatever it is, or sugar in their
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coffee, but knowing what your cues are is super important.
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Because then you could say, okay, I need to either just really make sure I eat this food
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at the right time, or maybe I shouldn't combine these two foods that are both kind of spikes
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But that kind of personalized information, I think, is where this field is really going
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to really understand like, these general rules are nice, but like you, you know, if you
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are going to have a piece of cake or a donut, or even a bowl of oatmeal, there's a time
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of day that's probably much healthier for you than others.
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We're going to take a quick break for your word from our sponsors.
00:21:31.020
There's a saying, it's eat breakfast like a king, lunch like a prince, and dinner like
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So the idea is you eat more of your calories, you know, at the beginning of the day, and
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they start tapering off as you get towards dinner time.
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Yeah, I think there's still more to be done in the field, but what we do know of it does
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I think there's a little bit of debate if it's breakfast like a king, or I would argue
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for some individuals, especially depending on your schedule, maybe lunch like a king
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But I think it's pretty well agreed upon now that a majority of your calories should be
00:22:10.380
And then your dinner should be probably a lower carb, higher protein, high fiber, but a more
00:22:16.860
And I think a lot of the evidence that has come out about like breakfast is so important
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I think both of those things have been true, but most of it is to avoid this late night binge
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And I think a lot of times we see like in modern society, especially among like college students
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or young adults, or I don't know, even working parents, people get really busy during the
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day, they grab something really small for breakfast, they might not have chance to eat
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And then they come home and they eat some huge amount of food at night and then relax.
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I mean, for all the different reasons, you're like starving yourself, your body then overeats,
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You have these really high levels of glucose, you're probably having a lot of fat buildup.
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And so those, you know, the opposite of that is definitely a problem.
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And I think a lot of evidence has actually really backed up that eating a larger meal in
00:23:12.180
the first half of your, you know, larger meals in the first half of your day and eating a
00:23:15.980
more modest dinner really does kind of help support the circadian system and it helps support
00:23:22.600
So you don't want to eat too late in the evening, you know, before you go to bed because your
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body's kind of going to sleep, insulin production is going down.
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If you eat later in the night, it's going to cause blood sugar problems, could possibly
00:23:39.600
Because you're just, you've got this big ball of food in your stomach and you're trying
00:23:43.620
But, you know, people in Europe, a lot of them, they seem to eat later in the evening
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Like they eat dinner at nine o'clock sometimes.
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I remember the first time I went there, we went out to go eat dinner at like eight and
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it was completely empty and I was very confused and no one showed up till like nine or ten.
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And as a circadian researcher, obviously I was curious about this.
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A lot of this is they actually have exposure to sun at pretty different times of day.
00:24:19.480
And if you switch the clock on the wall to align with when they actually see light, it's
00:24:27.300
And this becomes an issue in different parts of the world where there's these really large
00:24:35.040
And there's, you know, if you look at light availability in different parts of Europe,
00:24:44.220
And in another city, it might be completely dark, you know, at the same time of year.
00:24:48.560
And so when we think about circadian rhythms, we think about time, like 7 p.m., 8 p.m.
00:24:53.580
These are usually they're clocks on a wall and they're not actually sun time, but our body
00:24:58.960
is responding to sun more than artificial light.
00:25:02.880
And so when you have these shifted, you know, light availability or sun availability,
00:25:07.700
you typically do get these shifts in behavioral patterns.
00:25:14.240
They also typically go to bed a little bit later.
00:25:16.820
They also usually have a siesta in the middle of the day where they get to take a break and
00:25:22.120
And so they have kind of different overall schedules.
00:25:25.560
And so it's not the same like I ate at 9 p.m., but I have to go to bed at 10 p.m.
00:25:31.020
to get up to be able to leave super early in the morning.
00:25:34.940
And their light is also a little bit delayed, which does account for a lot of those differences.
00:25:42.340
So there's no one size fits all prescription for this stuff.
00:25:45.820
It's like, well, you can only eat from this time to this time.
00:25:48.240
It's going to depend on one, you know, just the environment you're in, not only the physical
00:25:53.720
environment, how much sunlight you're getting, but also the social environment that can train
00:26:00.660
But it also, every person has their own unique chronotype.
00:26:04.060
And there's some people who are night owls, like where they wake up later and then they
00:26:09.140
So those individuals who are night owls might be able to eat later in the evening, 8 o'clock,
00:26:15.160
And they're not going to go to bed for three or four hours still.
00:26:23.740
The problem with night owls are, and I tend to be a later person as well.
00:26:30.540
I know it can be, people kind of put it in a negative light a lot, and I don't think
00:26:34.920
The problem is, is that if you're staying up late, it also means you should be getting
00:26:39.860
up late and still getting light at a reasonable amount of light.
00:26:43.980
And if you're getting up super late or going to bed super late and you're not getting a
00:26:47.340
lot of light, that can lead to its own kind of issues.
00:26:50.440
And if you are, you know, eating really late after it's been dark for a very long time,
00:26:55.040
you still could potentially have some melatonin coming up where that's not the best situation.
00:26:59.240
And this also gets into if you really are a true late type or not.
00:27:05.400
So there are circadian mutations that can make you an extreme morning person or an extreme
00:27:15.760
I like to stay up till midnight or one or even two.
00:27:18.020
These are like, I cannot fall asleep before three or 4 a.m.
00:27:24.260
Or there are people like, I can't stay awake past 6 or 7 p.m.
00:27:37.540
And your chronotype can oscillate a bit throughout your life.
00:27:40.800
You know, little kids tend to be earlier risers.
00:27:43.060
When you go through puberty, you tend to delay a bit.
00:27:46.940
And I think there are biological mechanisms for that.
00:27:49.280
But some really cool work has been done looking in different populations around the world,
00:27:55.160
comparing individuals that don't have electricity, that are living off of natural light and fire
00:28:01.060
light versus people living within 100 miles but have full electricity.
00:28:07.040
And they found the people that live without electricity go to bed earlier, like all of them.
00:28:16.060
And there's even a study done in Colorado that showed that if you take individuals and
00:28:22.300
you put them camping where they only have firelight for like a week or two weeks, that
00:28:28.740
And so we think a lot of the reasons why so many of us are later types is not just because
00:28:33.380
of our chronobiology, but because we get a lot of artificial light.
00:28:38.020
You know, after a long day's work, maybe you're also taking care of kids.
00:28:41.020
And then the kids go to bed and it's like, oh, I just want to relax for an hour and watch
00:28:44.840
the show and maybe you want to have a snack with it, you know?
00:28:48.280
And then it's like we get kind of our relief then.
00:28:51.440
And so we end up staying up later really through these choices to stimulate ourselves in that
00:28:56.160
way to give ourselves some kind of entertainment or whatnot, or just, you know, work or whatever
00:29:00.220
it is where we end up staying up later than our bodies probably would want to.
00:29:03.780
And so if you take a lot of that stimulus away, people generally tend to shift a little bit
00:29:11.620
But I think trying to kind of listen to your body more than your schedule or a clock on
00:29:16.080
the wall is not always the easiest thing to do, but it's probably much healthier for you.
00:29:21.920
You mentioned some research done on shift workers and how the circadian rhythm affects their
00:29:28.240
I know I'm sure there's a lot of people listening to this podcast.
00:29:30.140
They might be a shift worker, maybe they're a first responder, a nurse, doctor, maybe they
00:29:34.460
just work a shift at a factory that's at nighttime.
00:29:37.840
What does the research say about how their irregular sleep schedule affects their metabolism?
00:29:45.040
Yeah, so I think shift work is so important to study.
00:29:48.620
And the crazy thing is they're almost never included in clinical trials.
00:29:51.940
I mean, it's like 0.0001% of clinical trials are including shift workers, even though they probably
00:29:59.960
And that's just because shift work itself is so confounding.
00:30:02.840
So like you said, obviously, if you're working in the middle of the night or working very late
00:30:07.280
or very early or having a moving schedule, your sleep is going to get disrupted.
00:30:11.980
Not being able to sleep adequate amount has also been shown to lead to weight gain, to lead
00:30:17.680
to increased glucose intolerance, higher A1C levels, which is, you know, when we talk about
00:30:22.840
hemoglobin A1C, it's like an estimate of like glucose for the past three months, but it's
00:30:28.360
All those things get worse when you have any form of sleep deprivation, even if you're still
00:30:32.580
sleeping at night, but it's, you know, really short sleeps.
00:30:35.880
The other thing that shift work does, though, is it really changes when you eat.
00:30:39.200
You know, if you're working a night shift, you're probably going to have to eat at night.
00:30:44.060
And that's kind of your functional time then, right?
00:30:47.200
But even though you're awake and you're active, your body's still not processing that food the
00:30:51.380
same way. And I think the best data we have from that is in like simulated shift work where
00:30:57.940
people are brought into the lab, given standardized meals, and you can see that they don't process
00:31:01.800
the food the same way. They do have higher glucose responses. They stay higher longer.
00:31:07.140
And then again, it's not just at that time. It's not just, oh, at night, my glucose was
00:31:12.420
compromised. The next day when you eat, your response to glucose is also compromised and you're
00:31:17.680
having poor glucose regulation. And so that's a really big problem we're trying to face.
00:31:23.520
In our own work, we did a randomized control trial in firefighters in San Diego County that
00:31:28.400
worked 24-hour shifts. We were able to put them on a time-restricted eating diet. I mean,
00:31:33.120
this was really mainly a feasibility study, but they were able to do it. Now, we started with them
00:31:38.120
because it's probably one of the easier shifts to do that with because they're working a 24-hour
00:31:42.020
shift. Their day is still their day. They're still mainly up. They might take a nap, but they're still
00:31:46.020
awake during the day. They eat lunch and dinner together. So they have pretty regular meals,
00:31:51.600
but they are working the full 24 hours. So they're getting on calls throughout the night. They're
00:31:55.720
getting woken up. All these other things are going on. And a lot of times they would get a snack in
00:32:00.080
the middle or people would bring in treats. So they were eating throughout the night, but they found
00:32:03.720
they were able to stop those extra eatings throughout the night. They were able to eat within a 10-hour
00:32:07.640
window. And of the participants who did have cardiometabolic disorders, we saw big improvements in
00:32:13.180
HbA1c. So glucose regulation, we saw improvements in diastolic blood pressure and overall energy
00:32:19.460
levels. People were feeling better. And so that was really exciting to see. And we even saw in the
00:32:24.600
full group, a decrease in very low density lipoprotein, which is kind of a worse version
00:32:30.060
of LDL cholesterol. When you think of that, it's like the bigger version of it that really leads to
00:32:35.120
these plaques in the heart. And we saw that those were getting smaller and that was really exciting to
00:32:39.600
see. And so I've recently been funded to do a new study in nurses and nursing assistants that
00:32:46.320
work night shifts. And we're trying to see if time-restricted eating is possible within that
00:32:51.300
group. And we're also trying to test out if a low glycemic snack at night may still give them some
00:32:57.240
benefits, even if it doesn't give them the full benefits, just out of feasibility alone. Because
00:33:02.640
the problem with working with shift work is we know it's bad for your circadian system,
00:33:06.520
but it's absolutely necessary. We need first responders. There's some jobs hopefully some
00:33:12.900
people don't have to do, but their most shift work is really out of necessity. And so we can't
00:33:18.340
change when they get to sleep. We can't change their light exposure most of the time, but we could
00:33:22.420
potentially change when they eat. And so we're seeing this as a potential window to be able to
00:33:26.920
help this extremely valuable group of people. Okay. So it sounds like if you are a shift worker,
00:33:32.700
the goal there is if you're staying up late at night or throughout the night, is it just to try
00:33:39.520
to eat during a 10 hour window, try not to eat at night and try to eat your calories during the day
00:33:43.820
when you can? Yeah. I mean, that's what we're trying to really figure out because there's just
00:33:48.400
not a lot of science there yet. I mean, theoretically, yes. I think the general logic and
00:33:52.760
based off the in-lab studies, which are only over a few days and very short periods of time,
00:33:57.200
but I think the logic really is that you're not able to process especially glucose more than other
00:34:03.100
macronutrients. And so I think having low glycemic snacks is probably going to be better. You know,
00:34:08.860
if you have to choose between a hard boiled egg and a big bowl of pasta, go for the hard boiled egg
00:34:13.940
or some nuts, something that could give you some energy and satiate you and maybe give you something
00:34:20.160
to nibble on because eating is also a big stimulatory cue for alertness. But yeah, lower glycemic foods,
00:34:26.900
smaller portions, so far it looks like that's what would be better if you can't just, you know,
00:34:33.400
completely fast at all. If you are able to fast through the night and keep a regular eating time,
00:34:38.840
you know, like to match with the days where you aren't working and eating normally during the day
00:34:44.080
and trying to keep to that, I think that's ideal. And then our hypothesis is that, yeah, really trying
00:34:48.880
to decrease the amount of carbs and decrease the total amount of calories that you're getting at night
00:34:53.260
would be kind of a good in-between compromise. Okay. So those are some general ideas, but I guess
00:34:58.040
more research is forthcoming. We'll have to stay tuned for that. You mentioned that time-restricted
00:35:02.700
eating can be seen as a form of intermittent fasting. How does intermittent fasting, I'm talking
00:35:08.880
like extended fast here, how does it affect our circadian rhythm or does it affect our circadian
00:35:15.200
rhythm? Yeah. So intermittent fasting is such a vague term. You know, it could mean a lot of
00:35:20.200
different things. I think the most common versions are like a five, two diet where five days a week,
00:35:24.280
you do whatever you want. And two days a week, you have pretty intense caloric restriction. And then
00:35:29.660
the other would just be like an eight hour, six hour diet, which is fairly similar to time-restricted
00:35:34.320
eating, but those usually don't keep a consistent eating window, which is really not the point I think,
00:35:40.880
which, you know, but the idea is usually of intermittent fasting is to decrease calories as well as
00:35:45.900
getting these longer periods of time where you're not eating. They can affect the system. I think of
00:35:51.360
them kind of like a cleaning out period of some sort. You know, if you think about nutrient
00:35:55.900
availability as a cue, eating all the time is kind of an abundance of cues. It's kind of constantly
00:36:01.160
resetting. Fasting kind of allows the natural rhythms to tick on their own a little bit more,
00:36:06.780
kind of continue on their own. Because if you had no cues, you still have these internal rhythms that
00:36:10.880
would keep a 24 hour day, but food and light are some of the biggest cues you can give your body.
00:36:15.420
So fasting kind of relieves that cue. And I don't really think of it as a way of setting the system
00:36:20.660
at all. I think having regular food timings are more important for that aspect of it,
00:36:25.140
but longer term, faster, you know, a couple of days or a day, or just these low calorie periods
00:36:30.880
can be helpful metabolically for other reasons, not via the circadian system. You know, you can get
00:36:36.480
some increased ketone production. You can relieve some other stress on the system. It's almost like a
00:36:41.840
rinsing out. And if you look at, I mean, so many different cultures have incorporated fasting
00:36:47.180
over, you know, hundreds of years. And a lot of them aren't complete fast, similar to intermittent
00:36:52.880
fasting. A lot of them are not water only. Most are not water only. Most are, you know, like nuts
00:36:58.820
or dried fruits are sometimes allowed or bone broths or different things like that to allow for really
00:37:05.080
small amounts of calorie intake for maintenance, but really just trying to allow the body to probably
00:37:10.160
break down more fats, kind of cleaning out the system of sorts. And those can be helpful
00:37:15.040
occasionally. You know, a lot of people try to practice something like that, like, you know,
00:37:19.080
three or four times a year, but I don't think them think of them as much as a circadian input as they
00:37:24.960
are. Maybe you're looking more at a metabolic fasting kind of ketone glucose regulation system
00:37:30.080
that obviously the circadian system is involved in, but it's kind of coming at that system from a
00:37:34.900
different angle. Gotcha. Well, let's do a quick recap. I think we've talked about a lot of
00:37:38.600
interesting things here. So I think the big takeaways is, you know, your body has a rhythm
00:37:43.060
and when we eat can influence how our body responds to food we eat depending on the timing of it. So
00:37:50.500
I guess wait about an hour after waking up to eat to let your body kind of wake up. That's the first
00:37:56.100
takeaway. I think another takeaway, maybe postpone carbs till later in the day, like lunch, maybe use
00:38:03.280
more of your carbs. And then as you get closer to nighttime, eat your last meal three to four hours
00:38:08.460
before you go to bed and you should be good. Yeah, I think that's the easy way of thinking
00:38:13.020
about it. And again, like, you know, like we just said, it's all relative to when you sleep. So
00:38:17.240
try not to look at a clock on a wall or say, I have to eat by five because someone said this. It's,
00:38:22.780
I got to eat when it's right for my body to eat. And that might mean little delays or little advances.
00:38:28.680
But I think when you're thinking about trying to adopt like a time-restricted eating or something
00:38:32.720
like that, it's never about meal skipping. It's never about these like huge,
00:38:37.200
I'm starving myself. It's really just about aligning your food to when you're active.
00:38:41.900
And if you're not eating till, you know, two hours after you wake up, it could probably have carbs in
00:38:46.380
it. It's more of a don't wake up and eat a ton of carbs right in the morning. And yeah, I think late
00:38:51.520
morning or early afternoon is probably a better time for carbs, like you said. But really, it's just
00:38:56.920
aligning when you eat to when you're active and allowing your body to get a proper fast at night.
00:39:02.140
Fantastic. Well, Emily, it's been a great conversation. Where can people go to learn more about your work?
00:39:05.220
Yeah, so you can follow me on Twitter at Emily Manugian. You can also look us up at the Salk Institute
00:39:12.460
website, or we have a app that we run that we use for all of our clinical trials. But it's also free
00:39:19.100
for the public. It's completely nonprofit research app. It's not commercial at all called My Circadian
00:39:24.600
Clock. You can find us at mycircadianclock.org. And the app is free to use on any iPhone or Android
00:39:31.540
phone. And on our website, we also just have lots of information about circadian rhythms,
00:39:36.960
about time-restricted eating, about healthy lifestyle. So yeah, you can check us out anytime
00:39:41.560
there. Fantastic. Well, Emily Manugian, thanks for your time. It's been a pleasure.
00:39:47.040
My guest today is Emily Manugian. You can learn more about our work at salk.edu. That's S-A-L-K.E-D-U.
00:39:52.960
Also check out our show notes at awim.is slash whentoeat, where you can find links to resources
00:39:57.260
when we delve deeper into this topic. Well, that wraps up another edition of the AOM podcast. Make
00:40:09.080
sure to check out our website at artofmanlies.com, where you find our podcast archives, as well as
00:40:13.280
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00:40:16.960
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00:40:27.260
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00:40:31.040
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