Scientists Find Internal Clock Sets at Mealtime It is well known that many organisms have a "circadian clock" — a biological time-keeping mechanism that connects the body's rhythms to external light levels. Now, researchers have found a second internal clock connected to food consumption that can overrule the regular light-based clock.
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Scientists Find Internal Clock Sets at Mealtime

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Scientists Find Internal Clock Sets at Mealtime

Scientists Find Internal Clock Sets at Mealtime

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IRA FLATOW, host:

This is Talk of the Nation Science Friday. I'm Ira Flatow. A bit later in the hour, we'll talk about watching a supernova explode, and about the possible health effects of carbon nanotubes. But first, what sets your body's internal clock? We've known about, and felt our own internal body clocks in action. The circadian clock is what allows an animal to sync up its own body rhythms with the movements of the sun, adapt to the seasons. You know about this problem called, you know, you have Seasonal Affective Disorder, where you need a light box to help you get you going in the winter time because of the lack of light.

Now, researchers report there may be a second clock mechanism working in the brains of mice, and probably in other organisms, too, that can throw a monkey ranch into this light-based clock and reset it, and that all has to do with your eating patterns. Eating, how you eat may reset your clock. Joining me now to talk about it is Dr. Clifford Saper. He's the James Jackson Putnam Professor of Neurology and Neuroscience at Harvard Med School and Chairman of the Department of Neurology at Beth Israel Deaconess Medical Center in Boston, and one of the authors of a paper on the research published this week in the Journal Science. Welcome back to the program, Dr. Saper.

Dr. CLIFFORD SAPER (Professor, Neurology and Neuroscience, Harvard Med School, M.D., Ph.D): It's wonderful to be back, too.

FLATOW: Let's talk about the main light, the light cycles that we go through. We've all heard about that the circadian rhythm is moderated or modulated by sunlight, correct?

Dr. SAPER: Correct. In most people, most of the time, there's a clock called the suprachiasmatic nucleus, which sits in the base of the brain, right behind the eyes, and which provides all kinds of messages to the different body systems, about how to schedule events during the day to make maximum advantage of the timing. So, for example, your enzymes in your gastrointestinal system that just digest food will turn on several hours before you eat, so that the enzymes will be there at the right levels when the food comes through to be digested.

FLATOW: So this is the main regulatory mechanism.

Dr. SAPER. Exactly. This suprachiasmatic nucleus is like the master clock. It's sort of like the conductor in an orchestra. There are clocks, it turns out, in many other tissues in the body, including other parts of the brain, but everybody comes under the control of the suprachiasmatic nucleus.

FLATOW: Now, laboratory research shows that this can be reset by how you eat.

Dr. SAPER: Well it doesn't - when you eat, it doesn't really reset the suprachiasmatic nucleus. That was the real surprise. But instead, if an animal doesn't have food available for say 12 to 16 hours, and then suddenly it finds food during the part of the day when it normally would be asleep, a second clock turns on, a different set of nerve cells in the brain called the dorsomedial nucleus, and they basically hijack all of the machinery of the brain, and turn over all the circadian rhythms onto a new time zone that is consistent with you being awake and available the same time the next day, in case food becomes available then.

FLATOW: So, is it reset? What time of the day does it reset it to?

Dr. SAPER: Well, it depends when the food comes up. Let me give you an example. So, it's not a rare thing in the environment for small animals to find that the food source they normally eat is not available. Let's take the example of brown bats, which everybody thinks of as being very nocturnal animals. And that's true during the middle of the summer when it's warm out at night, and there are insects at night flying around for them to eat. But during the spring and the fall when it's cool in the evening, the insects don't fly around very much, and they're mainly flying toward late afternoon, and the bats actually start moving their activity pattern back into the daylight hours to take advantage when the food is really there. It turns out almost all organisms can do this. They can adapt to the food availability, and totally turn their biological rhythms upside down within a day or two to take advantage when there's really food there to be had.

FLATOW: Can we do that as humans, too?

Dr. SAPER: Well, I don't know that anybody has tried that in humans, but I would predict that we can, because this parts of the brain that do this trick are very old, and the same parts of the brain can be found in humans as it all other species, and every species of people I've looked at, mammals at least, seems to be able to this. So, the prediction would be that humans probably can do this as well.

FLATOW: And, for example, if we want to do away with jet lag or something like that, could we starve ourselves?

Dr. SAPER: Exactly. So, the prediction would be that if you want to engage the dorsomedial nucleus clock, the way to do it would be to take a fast of maybe 12 to 16 hours, and then eat breakfast, so to speak, on the same time that they eat breakfast in the country you're going to.

FLATOW: And that would reset your clock?

Dr. SAPER: That should do it. I don't know that anybody has ever tried this as a real experiment. Believe it or not today, with all the publicity on the internet, and in the newspapers, I've been getting emails from people who claim that they do this all the time, and that it works.

FLATOW: What about people who start snacking at midnight? They would then totally screw themselves up, wouldn't they?

Dr. SAPER: Well, they might. But it depends, apparently, the second clock requires a period of fasting to get it going. So, in experiments that other folks have done, a fast of about 12-16 hours is probably necessary before the sudden appearance of food will have this effect.

FLATOW: So, you have to be pretty hungry in other words.

Dr. SAPER: Exactly.

FLATOW: And then you can reset it. So, if you snack during the day, and you come around and you're still snacking at midnight, it's probably not - you're not...

Dr. SAPER: That's probably not going to do it.

FLATOW: Does this have anything to say about people who are trying to lose weight, and eating patterns, do you think?

Dr. SAPER: Well, it might if they were, for example, let's say somebody fasted all day, and ate only in the evening, it's possible that that could also alter their body rhythms. That's something that would also have to be tested.

FLATOW: What made you think about, you know, studying this issue?

Dr. SAPER: We didn't make this up, believe it or not. This has actually been - this phenomenon has been known for a long time. A fellow named Kirk Richter described it in the 1920s, and there have been a lot of people over the years who've looked into it. It turns out that the food has to be nutritive, it can't just be filling. So, if you give animals non-nutritive food flavored with artificial flavorings, that doesn't work. They have to have calories for them to entrain to the food. And people have tried different timing schedules, so if the animals are very hungry, they haven't eaten for maybe 20 hours, it works better than if they've just had 16 hours of fasting before hand. So, people have tried this in various ways, and we know quite a bit about the phenomenon, but nobody actually knew how it worked in the brain.

FLATOW: Does this mean that if you reset your clock, you also reset the fatigue in your body that if you're on jet lag and you haven't slept, and you fasted for those 12 to 16 hours, you don't feel as tired?

Dr. SAPER: It does actually seem to reset the wake-sleep cycle as well. So, if you haven't slept for a very long period of time, I think you're still going to be tired, but one of the things that people notice is that even if they have not slept all day, if you go to Japan for example, and you try to go to sleep at 11 o'clock on their time, which would be about noon back in Boston, it's very hard to go to sleep. Even though you may be very tired, you still can't fall asleep.

FLATOW: Yes. Right.

Dr. SAPER: And, that kind of a circadian rhythm of the ability to fall asleep is something that we think can be reset by this clock.

FLATOW: Let's use your example. Let's say you have fasted for 12 to 16 hours. You get to Japan, it's noon in Japan. Does your clock reset to noon or does it reset to dawn?

Dr. SAPER: Well, the super suprachiasmatic nucleus will continue to run. There are two clocks, two separate clocks running, if you fasted, and then re-fed. The suprachiasmatic nucleus will stay on the original time program, and then if it encounters light at the wrong time of the day, it will advance by one to two hours a day, until it catches up with the local time. But the dorsomedial nucleus clock, which is the one that's started by food, will start on precisely the time when the food is available, and that clock tends to dominate under most circumstances. So, it can actually give you a real shift in your, for example, ability to sleep.

FLATOW: So, if you want to reset it when you go back home, you have to do just the opposite and...

Dr. SAPER: Exactly. And most people, if you go to Japan for a week, that's the worst possible thing because it takes an entire week to reset to their time, and then you come back home, and it takes an entire week to set back to your home time. If you were to use this method, presumably you would be able to do it much more quickly.

FLATOW: Let's see if I can get a quick question in 1-800-989-8255. David in Saint Louis. Hi, David.

DAVID (Caller): Hi. I wondered what the doctor had to say about people that may work irregular schedules. I'm thinking of like nurses or you know, drivers at some variety that work day-time hours part of the week, and then work night-time hours a different part of the week. And I can take my response off the air.

FLATOW: Thanks, David.

Dr. SAPER: So, I would say that actually this would be another logical application of it, for shift workers. Particularly ones who have to shift their daily activities by eight hours at a crack, and often have to do it twice a week. And so, I would suggest they work a trial to see if it's possible to shift the clock by simply fasting for 16 hours, and then eating breakfast right before your shift begins at 11 pm. See if this can shift your clock enough to make it easier to stay up at night.

FLATOW: You have to really be motivated though, not to eat for 16 hours.

Dr. SAPER: Yes. You know, you'd think that that would be true. But you know, for example if you look at the Muslim world during Ramadan, virtually everybody does that. It's not that hard to do. So, if people really wanted to do it, I think that they could use it as a way to control their own body.

FLATOW: And this would be good for airline pilots too. People like that, although we don't want them starving.

(Soundbite of laughter)

FLATOW: If they're on auto-pilot…

Dr. SAPER: Well, you know, there are reasons to believe also that starvation increases wakefulness. When you don't want your airline pilot to do is to be really tired, and then to have a really good meal.

(Soundbite of laughter)

FLATOW: Yes, just to shift the clock.

Dr. SAPER: Exactly.

FLATOW: Well, that's the other question. Doesn't your body want to go to sleep after you - if you starve for 16 hours, and have a good meal, doesn't your body want to go to sleep instead of resetting to stay awake?

Dr. SAPER: That depends if you've been awake during that previous 16 hours. So, if you slept...

FLATOW: I see.

Dr. SAPER: On the airplane, and then have breakfast when you get there, this should work probably best going to Europe. You would stop eating at noon the day before. You would not eat on the airplane. You get to Europe, which turns out to be about midnight our time but about six or seven am in Europe, and then you have breakfast there.

FLATOW: So, the key is also to do this in the dark in other words. Dark - make sure your fast is happening in the dark.

Dr. SAPER: It probably doesn't make any difference. But it probably helps a little bit if you don't have the light interfering.

FLATOW: Well, Dr. Saper, I want to thank you for making all of our flying a little easier. There's nothing else to do to make flying easy these days. Maybe you've helped us out, at least making a little more comfortable when we're grinding our teeth up there. Thanks a lot for calling.

Dr. SAPER: You're welcome. Thank you.

FLATOW: Our guest today, Clifford Saper is the James Jackson Putnam Professor of Neurology and Neuroscience at Harvard Medical School, and Chairman of the Department of Neurology at Beth Israel Deaconess Medical Center in Boston. We're going to take a short break, and when we come back, we're going to talk about Serendipity, luck favors the prepared mind as we say in science, and Louis Pasteur made that famous. We'll talk with some scientists who had their minds prepared, and had a very lucky, fortunate and interesting sighting of a supernova. Stay with us. We'll be right back.

I'm Ira Flatow. This is Talk Of The Nation Science Friday, from NPR News.

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