Podcast #1,036: When to Eat — The Optimal Schedule for Metabolic Health

Podcast Archives | The Art of Manliness

When it comes to weight management and all-around good metabolic health, we most often think about what to eat. But my guest would say that it’s also crucial to think about when to eat,

Emily Manoogian is a chronobiologist and clinical researcher at the Salk Institute for Biological Studies. Today on the show, Emily shares how to create an optimal schedule for a healthy metabolism by aligning your eating schedule with your circadian rhythm. She explains when to start eating after waking, when to stop eating before bed, the importance of sticking to a set schedule, and what happens to your metabolism when you don’t follow these timing guidelines. We also talk about how to best distribute your calorie intake throughout the day and how to eat to mitigate the metabolic problems that come with being a shift worker.

Resources Related to the Podcast

• The Salk Institute
• My Circadian Clock app
• AoM Podcast #1,016: Unlock Better Sleep and Health by Harnessing Your Circadian Rhythm

Connect with Emily Manoogian

• Emily on LinkedIn
• Emily on X

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Read the Transcript

Brett McKay: Brett McKay here and welcome to another edition of The Art Manliness podcast. When it comes to weight management, all around good metabolic health, you most often think about what to eat. Well, my guest would say that it’s also crucial to think about when to eat. Emily Manoogian is a chronobiolgist and clinical researcher at the Salk Institute for biological studies. Today in the show, Emily shares how to create an optimal schedule for a healthy metabolism by aligning your eating schedule with your circadian rhythm. She explains when to start eating after waking, when to stop eating before bed, the importance of sticking to a set schedule. What happens to your metabolism if you don’t follow these timing guidelines. We also talk about how to best distribute your calorie intake throughout the day and how to eat to mitigate the metabolic problems that come with being a shift worker. After the show is over, check at our show notes at aom.is/whentoeat.

Alright, Emily Manoogian, welcome to the show.

Emily Manoogian: Thank you for having me.

Brett McKay: So you are a circadian rhythm researcher. You research all the the rhythms that happen in our body from sun up to sun down, and then in between two-hour sleeping. How did you get started in that and what led you to focus on the intersection between our circadian rhythm and eating?

Emily Manoogian: Yeah, so it started quite a while ago when I was an undergrad in college, and I actually took a class called hormones and behavior with Lance Kriegsfeld at UC Berkeley, and I was instantly enamored. I was just fascinated with the subject that all of these rhythms control everything within our body, and that wasn’t even the biological rhythms class, but it started to touch on rhythms because of seasonal reproduction and animals, and I fell in love with it so much, I bothered him until he let me into his lab. I took his next car of biological rhythms and I was kind of hooked, so then I did my PhD in neuroscience and behavior with Eric Bittman out in UMass Amherst, again with a neuro-endocrine focus, but I really got into hardcore circadian biology at that point. Trying to understand this mutant hamster that could phase shift 12 hours over a night, think like you could go to India and have no jet lag, and so I was trying to understand how this worked.

And it always comes back to the molecular clock, which was really kinda cool, but in that time, I realized I really wanted to use my knowledge of circadian rhythms to apply it to humans and to help other individuals, ’cause the only reason I knew all about this was ’cause I was taking these very specific courses and it really wasn’t public knowledge, and I thought that was kind of crazy, and so I had this amazing opportunity to come to the Salk Institute to work with Satchin Panda who mainly does wet lab and basic science, but had gotten into time-restricted eating through rodent studies and was just about to start clinical work, had just done one study as a pilot and brought me on to get into this whole new field and really understand how timing of eating affects human performance and human health, and I have been doing it ever since.

Brett McKay: A while back ago, we had circadian researcher, Russell Foster on the podcast to discuss circadian rhythms, but something we didn’t dig much into is the relationship between circadian rhythms in our metabolism, and I wanna make that the focus of our conversation ’cause it’s just really fascinating. Can you walk us through the metabolic changes our body goes through during a 24-hour period?

Emily Manoogian: Yeah, absolutely, and caveat to this is when you’re talking about metabolism, it’s not like you’re only talking about the stomach or the gut, it’s your whole body works on metabolizing things. You could think as muscle as your biggest metabolic organ in a lot of ways. So it’s really into this whole body system, and the circadian system controls pretty much every organ in your body. So when you’re sleeping, your body is trying to… Hopefully, you’re fasting as well, and we’ll kinda circle back to this, we’ll kinda walk through a day, so when you’re sleeping, hopefully you’re fasting and your body is actually able to break down fats that you’ve built up over time or during the day, and release glucose into your body, because if you’re fasting at night, you’re not taking in new sugars, and your body and your brain still need glucose to work, and so you need some glucose in your body and going through your blood, and so your fat can be broken down. Glucagon is released to try to get that back into your blood.

When you wake up, you actually have this little spike in cortisol just before you wake up and that helps your body wake up for the day, you also get your sharpest rise in blood pressure, and that kind of wakes your body up, and for some people, this can also… You’ll also see a little increase in glucose in the blood just from getting up and started to walk around because your muscles need that glucose, sometimes it can rise just a little bit because of that, then you’re really alert in the morning, your brain is very capable, your body is starting to get going, and your circadian rhythms have also organized, worked with your liver to create enzymes to be able to break down food. So you’re actually very able to break down food and digest a high amount of calories in the morning. So we generally think kind of like an hour to maybe three after you’ve woken up is probably the best time to be able to process a big meal without having giant glucose spikes or any other kind of negative consequences, ’cause your body is really up and moving, and then throughout the day while you’re active, your body is still very able to digest a lot of calories, a lot of different types of macronutrients, and that’s really kind of when you should be eating is when you’re active.

As you get later in the day, again, having your last meal in the early evening or even not too late into the night where you’re getting too close to bed, it’s not too big of a problem, but the issue becomes is when people don’t eat much during the day and then eat this huge meals at night, and you’re really not able to process these really huge meals at night or very late at night, because your body is starting to get ready for rest, meaning it’s not producing all the enzymes you would need to break everything down, it’s not gonna be able to use up all those calories you just ate and a lot of times after dinner, people are sitting down, they’re not really gonna be using a lot of that, and when that happens, that becomes a little bit of a problem for, it just kind of staying in your body, not being fully processed, and then you’re not gonna get to break down those fats at night. The other thing that’s happening at night is melatonin starts to be secreted, and melatonin is really inhibited by light. This is why it happens in the evening. It also is regulated by the circadian system, and melatonin helps you fall asleep.

It also helps coordinate your metabolism by suppressing insulin secretion, so if you’re eating really late at night when your body is tired and it’s dark, you don’t have insulin in your blood to be able to take that glucose out of your blood and pack it away, and so this is why when you eat a lot right before you go to bed, your glucose levels will actually go really high and stay high sometimes for many hours, and that will completely inhibit any fat breakdown or anything like that. So depending on when you eat will kind of change what your body is doing at different times of day, but if you consolidate your food to your active phase, then you can kind of fast and break down fats at night and then use up a lot of the fuel you’re taking in during the day.

Brett McKay: That’s really interesting. I wanna go back to when we’re sleeping, so when we’re asleep, our body primarily uses… It’s breaking down fat. There’s a process where your body can turn fat into glucose, what’s it, glyco… What’s it… There’s a name for it.

Emily Manoogian: Gluconeogenesis.

Brett McKay: Gluconeogenesis. Right.

Emily Manoogian: Yeah.

Brett McKay: But I also know that our body stores glucose in our liver. Does our body…

Emily Manoogian: Yeah.

Brett McKay: Use that glucose supply when we’re asleep?

Emily Manoogian: Yeah, so you can release glucose from your liver. Absolutely. And one of the problems with getting too much glucose or having high levels or not being able to break things down is over time, you can also get fatty liver disease, and this is really tricky because we know it’s a common problem, but it’s not very often assessed, just because the testing for this is quite invasive and there’s not really much you can do about it, aside from healthier diet and also I would say eating at the right time of day, but research is going on to really determine how effective that is, but you can get this fatty liver disease where if you don’t use up a lot of these sugars that are in your liver, you can develop fat deposits within the liver and over time that makes it so the liver doesn’t function properly.

Brett McKay: I know some people, particularly when they’re pre-diabetic, when they wake up or even before they wake up, they have a huge glucose spike, like it can be 120 when they hadn’t eaten anything in hours, what’s going on with metabolism to cause that?

Emily Manoogian: Yeah, so when you get into things like pre-diabetes or type 2 diabetes, it’s not a normal system anymore. It’s not like it’s just higher levels of the same system. That means that the glucose regulation is compromised, and there’s not one way that it can be compromised. In type 2, there’s many different sub-categories, and there’s different mechanisms for why that’s happening, so depending on the individual, I could give you a different answer, but you do see this in some individuals where when they first wake up, especially sometimes when they go for a walk, they’ll see this big jump, and I’ve seen this in individuals with… Women with gestational diabetes, sometimes they were taking their finger pricks and they would go for a walk first, and that would actually cause their glucose to spike, and part of that is your muscles and stuff do need glucose, and so you do naturally get a small amount of glucose increased by just getting up and being active, but in those individuals, it’s kind of oh the system’s over-responding, and this is where you have some type of insulin resistance or you have some type of other issue going on that’s causing the glucose regulation to be maladaptive.

Brett McKay: So when we’re waking up, we have an initial glucose spike, it’s not too much, if you’re healthy, it’s not gonna be huge, but it’s just enough to get your body going, and then the circadian rhythm is also gonna start to bring on the insulin system. So insulin might not be ready for you to eat pancakes and syrup right off the bat, it might take an hour or two before your pancreas is really pumping insulin out so you can start shuttling glucose into your muscles.

Emily Manoogian: Yeah, and part of that is melatonin suppressing insulin, right. So melatonin, we think of it at night, but it peaks like in the middle of your night, and so it’s still pretty high for a while, and so it needs to come down, so things like getting a lot of really bright light in the morning and letting your body wake up for like an hour. That melatonin will then have plenty of time to shut down, your body is ready to eat, which is why we usually recommend waiting at least an hour after you wake up to eat, so your body is able to process that because people think about late night eating being a problem, and I think it really is, but super early eating is also a problem, and I think you see that more in individuals that might have a really early commute and have jobs where they can’t eat on the job. I see teachers doing this a lot, where they’re like, I got to eat breakfast, but they end up eating breakfast like in the dark at 5:00 in the morning. And that’s not healthy either.

Brett McKay: Okay, so we still have some melatonin in our system when we first wake up and that suppresses insulin production, and then as the day progresses, your metabolism is turned on and you start releasing insulin, and then as we get closer to night, melatonin is increasing again, which tells insulin production, alright, it’s time to go to sleep. We don’t need you anymore, and then you’re going back through that sleep process, so how can we put these pieces together and use this information of how our circadian rhythm manages our metabolism to optimize metabolic health?

Emily Manoogian: Yeah, so when it comes down to it, it’s kind of obvious things when you think about it. It’s allowing your body to fast at night and really eating when you’re active, and that sounds extremely simplified, but that’s kind of what the answer is, right, so how you actually would apply that. So we study a dietary intervention known as time-restricted eating, some people consider it a form of intermittent fasting, unlike other forms of intermittent fasting, it doesn’t require any type of caloric restriction, it can be combined with it, but it’s not required for it.

And really, it’s just eating at the same eating window, so usually an eight or 10-hour eating window, so for example, 9:00 to 7:00 PM, but it should be customized to your schedule, so someone who wakes up at 6:00 AM every day is gonna have a different eating window than someone who wakes up at 9:00 AM every day, it should be adjusted to fit your schedule, and it should be the same eating window every day, and the way we’d say to usually figure that out is think about what your normal sleep times are. Hopefully, you’re at least trying to sleep for eight hours a day, I know a lot of us don’t get that, but that should at least be the goal, and then say, wait at least one hour after you wake up and stop eating at least three hours before you go to bed, that gives you now, a 12-hour window. And then pick the 10 hours that work for you. And usually that’s decided by a family meal and kind of working backwards that way.

And just that simple thing of saying, I’m gonna eat at the same times, I’m gonna give that cue to my circadian rhythms that when I eat, I’m telling all the clocks within my body what time it is just through nutrient availability and the stimulation that food gives to your brain as well, but now you’re saying, okay, here’s a regular cue, my circadian rhythms can rely on that, and then the really cool thing about the circadian system is it’s anticipatory. It’s not a reactive like you ate, and so now I’m gonna do something. It’s I know you usually eat at this time, so I’m gonna prepare enzymes to be able to break down food for you at that time, and so if you eat at regular times, your body will be more prepared to break down food at that time and process it properly and then getting a regular fast that’s long enough for your body, at least like a 14-hour fast each day, most of that is while you’re asleep, but getting that daily fast is super important, so you can actually break down fats and use up sugars, so you’re not creating this overload of resources that your body can’t handle and over time leads to a lot of issues.

Brett McKay: Yeah, that sounds about what I do with my schedule, so I wake up at 5:30, and then I don’t eat until 7:00 and then…

Emily Manoogian: Perfect.

Brett McKay: Eat during the day, and then our dinner is usually around 6:00, 6:30, and then nothing after that before I go to bed.

Emily Manoogian: Yeah, I think that’s pretty reasonable. That’s like, what, 11, 11 and a half hours. But even with that, I don’t think it’s hurting you in any way, you’re aligning it to your active phase, you’re waiting until you wake up, you’re getting at least probably a three-hour chunk before you go to bed. I think that’s absolutely fine. I think that’s a very reasonable way to eat and you’re aligning that with all the other cues that you’re giving your body, like light and activity and social interaction and stress and exercise, all those other things are aligning, so your body actually knows what time it is, and just the simple act of supporting your circadian rhythms is super helpful for almost every aspect of physiology.

Brett McKay: Okay, so you wanna have your first meal at least an hour after you wake up and then stop eating three to four hours before you go to bed, so you’re aiming for an eight to 10 hour eating window overall, and what this does, it ensures you’re eating when your metabolism is most active and then fasting when it’s less so. And also the other takeaway too is you wanna eat at the same consistent times every day, ’cause that helps your body be prepared to process food, so you mentioned that there are some people who don’t stick to the sort of time-restricted, regular schedule. What happens to our metabolism whenever we eat too soon after waking up and then eat too late before going to bed.

Emily Manoogian: Yeah, so part of this gets back to melatonin again, right, when you eat too soon, you just might not have insulin enough in your system where your glucose levels can get very high. This is also a more common problem in the United States, because a lot of our breakfast and not just the United States, but it tends to be a bigger issue here, a lot of the Western breakfast is very carb-heavy, and there’s also been some really interesting science into food desires at different times of day, and the things that we crave when we’re tired, like late at night or early morning are not healthy foods. We do not crave a salad or just avocados in the morning, we crave a donut or a sugary coffee or something to give ourselves a treat because we had to wake up and we’re so tired, so we try to treat ourselves with these really unhealthy foods, and at those really late times, we’re specifically not able to process them properly, so eating super early in the morning, again, you’re just gonna have higher glucose response, it’s probably gonna stay higher for longer. Same thing at night when you’re eating really late at night, you get that same kind of thing.

What’s really interesting though, and some really beautiful science has come out in the past couple of years from multiple groups now, but Frank Scheer’s group at Harvard did this really nice study where they had participants in the lab and they provided meals to them and they’d either give them dinner at 7:00 PM or to another set of participants, they would give them dinner around 10:00 PM, and it was the same quality of food, but the participants that got it really late, not only had a higher glucose response but they stayed to have elevated glucose responses for hours later into the night.

And what was really interesting is, even though they eventually got back down to normal fasting glucose levels, but the next morning, they gave them a glucose tolerance test, and the ones who had eaten the night before later, they didn’t respond to glucose as well the next morning either. They had a higher response to it and it stayed elevated longer, and there’s some nice work from Australia that came out also recently doing this in-lab model of shift work where they had people do simulated night shifts and either eat a large meal, a small meal, or nothing during the night while they were working, and even though they were active, that eating during the night led to compromised glucose the next morning in both groups that had any kind of food, but it was worse in the larger meal, so it seems like eating really late at night compromises both the glucose at that time and while you’re sleeping, which can also cause you to have a worse quality of sleep, which has its own downstream effects, but it also compromises your glucose the next day and potentially for multiple days after.

So it really does seem to be throwing off the system in a pretty significant manner and this constant disruption to glucose regulation, constant levels of higher glucose that leads to pre-diabetes and type 2 diabetes.

Brett McKay: And it sounds like too if you are managing pre-diabetes or type 2 diabetes, you have to think, maybe what this research suggests not only think about the type of foods you’re eating, but when you eat them can have a big influence as well.

Emily Manoogian: 100%.

Brett McKay: Yeah. Yeah, I’ve seen first-hand how timing your food intake can change how your body responds to it. So a while back ago, I tried out the continuous glucose monitor, I don’t have pre-diabetes or anything, but I wanted to try it out, and something I saw was when I was doing it, my first meal would be very carb heavy, like a bowl of oatmeal and some yogurt and some blueberries, and my glucose would just spike and would stay spiked for a really long period of time. So something I did is I swapped to a kind of a lower carb meals, it was just like eggs, yeah just basically eggs and like a low carb wrap, and I moved my oatmeal later in the morning, and then like… Yeah, the carb spike went away, and then after I had my oatmeal later in the morning, I didn’t have the same sort of spike as I had when I ate it first thing in the morning.

Emily Manoogian: Yeah, I’ve seen that so many times. And the really great thing about continuous glucose monitors, or I’m probably gonna say it short hand, so they’re also called CGM, is they tell you so much about how you specifically like you as a person, respond to different foods because it’s different for different people, and just like you said the same food can cause a different reaction at different times of day, and being able to wear a continuous glucose monitor is really powerful ’cause you can learn so much about yourself, you might learn just like you said, you can eat a meal, just not first thing, you have to eat it a little later, that same might be true for a donut, or maybe you can’t have it early or maybe you can’t have it late, but in the afternoon, maybe it’s not as bad for your system, or people find out maybe they really have big spikes in response to rice, and you might have someone else eating the exact same meal that doesn’t have that same response, even at the same time. There’s individual differences between people, but usually people have something that gets them, whether it’s rice or pizza or donuts or oatmeal, or whatever it is or sugar in their coffee.

But knowing what your cues are is super important because then you could say, okay, I need to either just really make sure I eat this food at the right time, or maybe I shouldn’t combine these two foods that are both kind of spikes for me, but that kind of personalized information, I think is where this field is really going to really understand, these general rules are nice, but if you are gonna have a piece of cake or a donut or even a bowl of oatmeal, there’s a time of day that’s probably much healthier for you than others.

Brett McKay: We’re gonna take a quick break for a word from our sponsors. And now, back to the show, there’s a saying eat breakfast like a king, lunch like a prince, and dinner like a pauper, so the idea is you eat more of your calories at the beginning of the day and then start tapering off as you get towards dinner time. Does science back up that adage?

Emily Manoogian: Yeah, I think there’s still more to be done in the field, but what we do know of it does seem to be pretty true. I think there’s a little bit of debate if it’s breakfast like a king or… I would argue for some individuals, especially depending on your schedule, maybe lunch like a king would also be fine, but I think it’s pretty well agreed upon now that a majority of your calories should be consumed in the first half of your day, and then your dinner should be probably a lower carb, higher protein, high fiber, but a more modest meal, and I think a lot of the evidence that has come out about breakfast is so important or late night eating is really bad, I think both of those things have been true, but most of it is to avoid this late night binge eating, and I think a lot of times we see in modern society, especially among college students or young adults, or I don’t know, even working parents, people get really busy during the day, they grab something really small for breakfast, they might not have a chance to eat much for lunch and then they go oh barely ate today, and then they come home and they eat some huge amount of food at night and then relax, that is obviously very bad for your system, for all the different reasons you’re starving yourself, your body then over-eats, then you’re just sitting on it, you have these really high levels of glucose, you’re probably having a lot of fat build up, and so those…

The opposite of that is definitely a problem, and I think a lot of evidence has actually really backed up that eating larger meals in the first half of your day, and eating a more modest dinner really does kind of help support the Circadian system and it helps support good metabolic health.

Brett McKay: So you don’t wanna eat too late in the evening before you go to bed because your body is going to sleep. Insulin production is going down. If you eat later in the night, it’s gonna cause blood sugar problems, can possibly potentially lead to weight gain. It can also just disrupt sleep ’cause you’re just… You’ve got this big ball of food in your stomach you’re trying to digest, but people in Europe, a lot of them, they seem to eat later in the evening without any problems, like they eat dinner at 9 o’clock sometimes. What do you think’s going on there?

Emily Manoogian: Yeah. So that gets really interesting. You think of Spain. Everyone thinks of Spain eating super late. I remember the first time I went there, we went out to go eat dinner at like 8:00, and it was completely empty, and I was very confused and no one showed up till 9:00 or 10:00, and that was kind of mindboggling to me and as a circadian researcher, obviously, I was curious about this. A lot of this is they actually have exposure to sun at pretty different times of day, they’re actually pretty delayed, and if you switch the clock on the wall to align with when they actually see light, it’s actually not very late for them, and this becomes an issue in different parts of the world where there’s these really large time zones that span large areas, and there’s… If you look at light availability in different parts of Europe, it might say 6:00 PM on the wall, and in one city it might be completely sunny, and in another city it might be completely dark at the same time of year. And so when we think about circadian rhythms, we think about time like 7:00 PM, 8:00 PM, these are usually their clocks on a wall, and they’re not actually sometimes, but our body is responding to sun more than artificial light.

And so when you have these shifted light availability or sun availability, you typically do get these shifts in behavioral patterns, and Spain is a big one of those, they also typically go to bed a little bit later, they also usually have a siesta in the middle of the day where they get to take a break and maybe a little bit nap, and so they have different overall schedules and so it’s not the same. I ate at 9:00 PM, but I have to go to bed at 10:00 PM to get up to be able to leave super early in the morning. Their schedule is a little bit delayed and their light is also a little bit delayed, which does account for a lot of those differences.

Brett McKay: Okay, so that’s interesting. So there’s no one-size-fits-all prescription for this stuff. It’s like well, you can only eat from this time to this time, it’s gonna depend on one, just the environment you’re in, not only the physical environment, how much sunlight you’re getting, but also the social environment, I can train your circadian rhythm in a certain way, but it can also…

Emily Manoogian: Absolutely.

Brett McKay: Every person has their own unique chronotype, and there’s some people who are night owls, where they wake up later, and then they go to bed later, so those individuals who are night owls might be able to eat later in the evening, 8 o’clock, 9 o’clock, and they’re not gonna go to bed for three or four hours still, and they’re gonna be fine. They probably won’t have any problems.

Emily Manoogian: Yeah, it gets a little complicated right? The problem with night owls, and I tend to be a later person as well, so no shame in saying night owl, I know it can be, people kind of put it in a negative light a lot, and I don’t think that’s fair. The problem is, is that if you’re staying up late, it also means you should be getting up late and still getting a reasonable amount of light, and if you’re getting up super late or going to bed super late and you’re not getting a lot of light, that can lead to its own kind of issues, and if you are eating really late after it’s been dark for a very long time, you still could potentially have some melatonin coming up where that’s not the best situation, and this also gets into if you really are a true late type or not, and there is some interesting science here, so there are circadian mutations that can make you an extreme morning person or an extreme late person. And these are not normal, I like to stay up till midnight or 1:00 or even 2:00. These are like, I cannot fall asleep before 3:00 or 4:00 AM, and I have to wake up at 11:00 or 12:00, or there are people like, I can’t stay awake past 6:00 or 7:00 PM, and I have to wake up by 4:00 AM, like these really intense differences.

Those are known genetic changes, and there probably are some spectrum, and your chronotype can oscillate a bit throughout your life, little kids tend to be earlier risers. When you go through puberty, you tend to delay a bit, and it comes a little bit earlier, and I think there are biological mechanisms for that, but some really cool work has been done looking in different populations around the world, comparing individuals that don’t have electricity that are living off of natural light and fire light versus people living within 100 miles but have full electricity, and they found the people that live without electricity go to bed earlier, like all of them, they go to bed earlier, they wake up earlier, they adjust it with the sun, and there is even a study done in Colorado that showed that if you take individuals and you put them camping where they only have fire light for a week or two weeks, that they all become a little bit earlier. And so we think a lot of the reasons why so many of us are later types is not just because of our chronobiology, but because we get a lot of artificial light after a long day’s work.

Maybe you’re also taking care of kids. And then the kids go to bed and it’s like, oh, I just wanna relax for an hour and watch the show. And maybe you wanna have a snack with it, and then it’s like we get kind of our reliefs in, and so we end up staying up later really through these choices to stimulate ourselves in that way to give ourselves some kind of entertainment or whatnot, or does work or whatever it is, where we end up staying up later than our bodies probably would want to, and so if you take a lot of the stimulus away, people generally tend to shift a little bit earlier, and that’s not always possible to do, but I think trying to listen to your body more than your schedule or clock on the wall is not always the easiest thing to do, but it’s probably much healthier for you.

Brett McKay: You mentioned some research done on shift workers and how the circadian rhythm affects their metabolism there. I know, I’m sure there’s a lot of people listening to this podcast, they might be a shift worker, maybe they’re a first responder, a nurse, doctor, maybe they just work a shift at a factory, it’s at night time. What does the research say about how their irregular sleep schedule affects their metabolism?

Emily Manoogian: Yeah, so I think shift work is so important to study, and the crazy thing is they’re almost never included in clinical trials, I mean, it’s like 0.0001% of clinical trials are including shift workers even though they probably have the biggest need. And that’s just because shift work itself is so confounding, so like you said, obviously if you’re working in the middle of the night or working very late or very early or having a moving schedule, your sleep is gonna get disrupted. Not being able to sleep adequate amount has also been shown to lead to weight gain, to lead to increased glucose intolerance, higher A1c levels, which is when we talk about hemoglobin A1C is like an estimate of glucose for the past three months, but it’s kind of the gold standard. All those things get worse when you have any form of sleep deprivation, even if you’re still sleeping at night, but it’s really short sleeps.

The other thing that shift or does though is it really changes when you eat. If you’re working a night shift, you’re probably gonna have to eat at night, and that’s kind of your functional time then, right. But even though you’re awake and you’re active, your body is still not processing that food the same way, and I think the best data we have from that is in simulated shift work where people are brought into the lab given standardized meals, and you can see that they don’t process the food the same way. They do have higher glucose responses, they stay higher longer, and then again, it’s not just at that time, it’s not just, oh, at night, my glucose was compromised the next day when you eat your to glucose is also compromised and you’re having poor glucose regulation, and so that’s a really big problem we’re trying to face in our own work. We did a randomized control trial in firefighters in San Diego County that worked 24-hour shifts. We were able to put them on a time-restricted eating diet, this is really mainly a feasibility study, but they were able to do it.

Now, we started with them because it’s probably one of the easier shifts to do that with because they’re working a 24-hour shift, their day is still their day, they’re still mainly up, they might take a nap, but they’re still awake during the day, they eat lunch and dinner together, and so they have pretty regular meals, but they are working the full 24 hours, so they’re getting on calls throughout the night, they’re getting woken up, all these other things are going on, and a lot of times they would get a snack in the middle or people would bring in treats, so they were eating throughout the night, but they found they were able to stop those extra eating throughout the night, they were able to eat within a 10-hour window, and of the participants who did have cardiometabolic disorders, we saw big improvements in HbA1c, so glucose regulation, we saw improvements in diastolic blood pressure, and overall energy levels, people were feeling better.

And so that was really exciting to see, and we even saw in the full group a decrease in very low density lipoprotein, which is kind of a worse version of LDL cholesterol, when you think of that, it’s like the bigger version of it that really leads to these plaques in the heart, and we saw that those were getting smaller and that was really exciting to see, and so I’ve recently been funded to do a new study in nurses and nursing assistants that work night shifts, and we’re trying to see if time-restricted eating is possible within that group.

And we’re also trying to test out if a low glycemic snack at night may still give them some benefits, even if it doesn’t give them the full benefits just out of feasibility alone, because the problem with working with shift work is we know it’s bad for your circadian system, but it’s absolutely necessary. We need first responders, we need all the… There’s some jobs, hopefully, some people don’t have to do, but their most shift work is really out of necessity, and so we can’t change when they get to sleep, we can’t change their light exposure most of the time, but we could potentially change when they eat and so we’re seeing this as a potential window to be able to help this extremely valuable group of people.

Brett McKay: Okay, so it sounds like if you are a shift worker, the goal there is if you’re staying up late at night or throughout the night, is it just to try to eat during a 10 hour window, try not to eat at night, and try to eat your calories during the day when you can?

Emily Manoogian: Yeah, that’s what we’re trying to really figure out because there’s just not a lot of science there yet. I mean, theoretically, yes. I think the general logic, and based off the in-lab studies, which are only over a few days and very short periods of time, but I think the logic really is that you’re not able to process especially glucose more than other macronutrients. And so I think having low glycemic snacks is probably gonna be better if you have to choose between a hard-boiled egg and a big bowl of pasta, go for the hard-boiled egg or some nuts, something that could give you some energy and satiate you and maybe give you something to nibble on because eating is also a big stimulatory cue for alertness, but yeah, lower glycemic food, smaller portions so far looks like that’s what would be better if you can’t just completely fast at all. If you are able to fast through the night and keep a regular eating time to match with the days where you aren’t working and eating normally during the day and trying to keep to that, I think that’s ideal, and then our hypothesis is that, yeah, really trying to decrease the amount of carbs and decrease the total amount of calories that you’re getting at night would be kind of a good in-between compromise.

Brett McKay: Okay, so those are some general ideas, but I guess more research is forthcoming. We’ll have to…

Emily Manoogian: Yeah, yeah.

Brett McKay: Stay tuned for that. You mentioned that time-restricted eating can be seen as a form of intermittent fasting. How does intermittent fasting… I’m talking like extended fast here, how does it affect our circadian rhythm or does it affect our circadian rhythm?

Emily Manoogian: Yeah, so intermittent fasting is such a vague term. It could mean a lot of different things. I think the most common versions are like a 5:2 diet, where five days a week you do whatever you want and two days a week, you have pretty intense caloric restriction, and then the other would just be like an eight-hour or six-hour diet, which is fairly similar to time-restricted eating, but those usually don’t keep a consistent eating window, which is really not the point, I think, but the idea is usually of interment fasting is to decrease calories as well as getting these longer periods of time where you’re not eating. They can affect the system, I think of them kind of like a cleaning out period of some sort, if you think about nutrient availability as a cue, eating all the time is kind of an abundance of cues, it’s kind of constantly resetting, fasting kind of allows the natural rhythms to tick on their own a little bit more, kinda continue on their own, ’cause if you had no cues, you still have these internal rhythms that would keep a 24-hour day, but food and light are some of the biggest cues you can give your body.

So fasting relieves that cue, and I don’t really think of it as a way of setting the system at all. I think having regular food timings are more important for that aspect of it, but longer term faster, a couple of days or a day or just these low calorie periods can be helpful metabolically for other reasons, not via the circadian system, you can get some increased ketone production, you can relieve some other stress on the system, it’s almost like a rinsing out and if you look at so many different cultures have incorporated fasting over hundreds of years, and a lot of them aren’t complete fast similar to intermittent fasting. A lot of them are not water only, most are not water only, most are, like nuts or dried fruits are sometimes allowed, or bone broth or different things like that, to allow for really small amounts of calorie intake for maintenance, but really just trying to allow the body to probably break down more fats, kind of cleaning out the system of sorts, and those can be helpful occasionally, a lot of people try to practice something like that, like three or four times a year, but I don’t think they think of them as much as a circadian input as they are, maybe you’re looking more at a metabolic fasting, ketone glucose regulation system that obviously the circadian system is involved in, but it’s kind of coming at that system from a different angle.

Brett McKay: Gotcha. Well, let’s do a quick recap. I think we’ve talked about a lot of interesting things here. So I think the big takeaway is your body has a rhythm, and when we eat can influence how our body responds to food we eat depending on the timing of it, so I guess wait about an hour after waking up to eat to let your body kinda wake up, that’s the first takeaway. I think another takeaway, maybe postpone carbs till later in the day, like lunch, maybe use more of your carbs, and then as you get closer to night time, eat your last meal three to four hours before you go to bed and you should be good.

Emily Manoogian: Yeah, I think that’s the easy way of thinking about it, and again, like we just said, it’s all relative to when you sleep, so try not to look at a clock on a wall or say, I have to eat by 5:00 because someone said this. It’s I gotta eat when it’s right for my body to eat, and that might mean little delays or little advances, but I think when you’re thinking about trying to adopt a time-restricted eating or something like that, it’s never about meal-skipping, it’s never about these huge, I’m starving myself, it’s really just about aligning your food to when you’re active, and if you’re not eating till two hours after you wake up, it could probably have carbs in 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 morning or early afternoon is probably a better time for carbs, like you said, but really it’s just aligning when you eat to when you’re active and allowing your body to get a proper fast at night.

Brett McKay: Fantastic. Well, Emily, it’s been a great conversation. Where can people go to learn more about your work?

Emily Manoogian: Yeah, so you can follow me on Twitter at @EmilyManoogian. You can also look us up at the Salk Institute website, or we have an app that we run that we use for all of our clinical trials, but it’s also free for the public, it’s a completely non-profit research app, it’s not commercial at all, called My Circadian Clock. You could find us at mycircadianclock.org, and the app is free to use on any iPhone or Android phone, and on our website, we also just have lots of information about circadian rhythms, about time-restricted eating, about healthy lifestyle, so yeah, you can check us out anytime there.

Brett McKay: Fantastic. Well, Emily Manoogian, thanks for your time. It’s been a pleasure.

Emily Manoogian: Thanks so much for having me.

Brett McKay: My guest today is Emily Manoogian. You can learn more about our work at salk.edu, that’s S-A-L-K.edu. Also check our show notes at aom.is/whentoeat where you can find links to resources, we delve deeper into this topic.

Well, that wraps up another edition of The AOM podcast, make sure to check on our website at artofmanliness.com where you can our podcast archives, as well as thousands of articles that we’ve written over the years about pretty much anything you think of, and if you haven’t done so already, I’d appreciate if you take one minute to give us a review on Apple Podcast or Spotify, it helps out a lot. And if you’ve done that already, thank you. Please consider sharing the show with a friend or family member who you think will get something out of it. As always, thank you for the continued support. Until next time, it’s Brett McKay, reminding you to not only listen to AOM Podcast but put what you’ve heard into action.

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