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Do you want to start feeling better?

Yes, Where Do I Start?

The Science Behind Intermittent Fasting and Circadian Rhythm

When you eat is as important as what you eat, with Dr. Satchin Panda.

Intermittent fasting (or time-restricted feeding) is a method of limiting the time window you eat each day to a consistent number of hours and a consistent time each day. Between 8-10 hours of eating window is considered optimal in humans, which leaves 14-16 hours for your body to fast. This period allows your organs a break from digesting so they can heal. This can reduce leaky gut and improve blood sugar and blood pressure. Early studies showed that genetically identical mice fed the same number of calories became unhealthy when allowed to “free feed” (eat at any time) but lost weight when their feeding hours were restricted. Studies on humans have shown the same response. As a general rule of thumb, stay within a 10-hour eating window for at least 12 weeks to see the best results, and stop eating at least 2-3 hours before sleeping.

Dr. R’s Fast Facts Summary

Light exposure

  • Blue light is rich in daylight
    • Humans have what is called Melanopsin which senses blue light and helps to set our circadian rhythm
  • We require 500 lux – 1000 lux of light to fully activate and synchronize our internal clock
  • Most lack bright light exposure, due to our current indoor lifestyle which compromises our sleep and overall health

How to get better sleep

  • Step outside for 30 min per day
    • Even on a cloudy day outdoor light is about 10,000 lux
  • Reduce blue light at night
  • Refrain from eating 2-3 hrs before your bedtime

What is time restricted eating?

  • Eating all meals within a specified window of time each day, giving your body the opportunity to rest overnight, regenerate, and heal
  • Also referred to as intermittent fasting

Intermittent Fasting Defined

  • 8-10 hour eating window (16-14 hour of fasting) is doable for most people
  • Try not to eat 2-3 hrs before bedtime
    • During this time, melatonin begins to rise which can slow down the function of the pancreas so the pancreas does not produce enough insulin
    • Eating dinner too late stresses our stomach, intestines etc.
    • Better to have an early dinner
  • Having a larger meal in the first half of the day is a good thing

Benefits of Intermittent Fasting (IF)

  • IF has a number of benefits in the treatment of chronic health conditions like diabetes, obesity, digestive issues, heart disease, mental health, etc.
  • People tend to inadvertently reduce their alcohol and sugar intake
  • Optimizes digestion

When do you see results?

  • 3 months is a good time frame
    • 1st week – is difficult
    • 2nd week – most experience improvements in sleep
    • 6-10 weeks – many experience some weight loss, improvement in blood sugar and blood pressure
  • 10-12 weeks for gradual weight loss (some people have lost 70-80 lbs over a year)
  • Tip: Recording what you eat in the mycircadianclock app helps to keep the habit longer term

When to exercise?

  • Exercising in the evening has proven to be more beneficial overall, especially for professional athletes and those with diabetes
    • Exercise in the evening to better control blood sugar

Where to learn more

In This Episode

Episode Intro … 00:00:40
Light Exposure and Health … 00:02:55
Time-Restricted Feeding & Why It Matters … 00:09:22
Research on Intermittent Fasting (Human) … 00:13:36
Intermittent Fasting and Lowering Disease … 00:21:29
Optimal Fasting Time Window … 00:27:51
Building an Intermittent Fasting Habit … 00:35:42
When to Expect Results … 00:41:44
The Circadian Code … 00:46:42
Digestive Benefits from Intermittent Fasting … 00:51:07
Episode Wrap-Up … 00:53:31

Intermittent Fasting

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Episode Intro

Dr. Michael Ruscio, DC: Hi everyone. Welcome to Dr. Ruscio Radio. This is Dr. Ruscio. Today I am here with Satchin Panda and we’re going to be talking about circadian health and time-restricted feeding. Dr. Satchin, I really have to commend the work you are doing.

He is doing a terrific service for people, in terms of increasing their awareness of how detrimental inappropriate light exposure can be and also eating too late at night. I want to get into some of those details. Thank you so much for coming on the show today.

Dr. Satchin Panda: Thank you, I’m glad to be here.

DrMR:  Before we get into the topic, tell people about your background. Then we’ll launch into what I’m sure will be a fascinating conversation.

DrSP:   Well, I did my PhD in circadian rhythms. That was looking at how tiny plants tell time with their leaves, harvest sunlight, and then go back to sleep.

I learned a lot about how the circadian clock works in plants. The fascinating thing is, you can use the same principle of circadian timekeeping in plants (pond scum even), or humans and mice. So I moved to doing research in mice and fruit flies during my postdoctoral training.

Then, I have been with the Salk Institute for nearly 15 years now, and my lab works on circadian rhythm, specifically how the body keeps track of time and how these clocks of circadian rhythms respond to light, darkness, eating, fasting. We look at how we can combine all of this knowledge from basic science research to prevent, manage, or even treat some of the chronic diseases that affect millions of people.

DrMR:  And we’ve talked a few times in the past on the podcast regarding light exposure and how, specifically, blue light exposure at night is not good for one’s health. Just in case anyone in the audience hasn’t heard about that yet, can you give a short primer on that?

Light Exposure and Health

DrSP:   Yes. For many years—almost 75 years—scientists knew that the blind people who cannot see because they don’t have rod and cone light sensors in their eyes can still sense light. When these blind people fly from the East Coast to the West Coast or vice versa, they can re-adjust their sleep time in response to light. So there was this curiosity… there must be a light sensor in the eye that senses light and resets our clock. It also does many more things.

Almost 16 years ago, we discovered the role of the new blue light sensor, called melanopsin, in the circadian adjustment. It’s how our internal clock synchronizes with the outside world light-dark cycle.

That was a key discovery. The original discovery was around these mice, who have normal rod and cone cells, so they can the world around them (but they don’t have this blue light sensor called melanopsin). Although they can see everything, they cannot sense that light. So they can’t appropriately align their internal clock with the light-dark cycle.

Now, fast-forward 15, 16 years. That fundamental discovery—that this light sensor senses blue light which is very rich in sunlight or daylight—has led to other discoveries in my lab and in other peoples’ labs. For example, candlelight and firelight are a very poor source of blue light.

If you think about our ancestors up to, say, 150 years ago, when they were hunter-gatherers and they spent most of their time outdoors, they were getting a lot of blue light during the daytime, from sunlight or daylight on a cloudy day. And this bright blue light or bright daylight was enough to synchronize their circadian clock to a day-night cycle.

It was reducing their melatonin levels so that they were not feeling sleepy when they woke up in the morning. It was also increasing alertness. So they were feeling more happy and alert throughout the day. In the evening, even though they had access to a little candlelight or lamplight, that light was not sufficient to excite or to activate this blue light sensor, because the lamp or the candlelight doesn’t produce blue light.

As a result, even though there was candlelight burning, the brain thought it was nighttime. So it deduced that it should go to bed relatively early and people used to get a consolidated good night’s sleep.

Now, in the modern world, we spend most of our time indoors during the daytime. And a lot of us, unfortunately, do not have access to bright light. When you say bright light, actually this melanopsin sensor requires somewhere between 500 to 1000 lux of light to fully activate and synchronize our internal clock to the outside world.

The question is, how do you measure light? How much is 500 lux, how much is 100 lux, and how much light is on a cloudy day or a sunny day? Many of you may know some apps that will measure that. Actually, our lab also made an app called My Lux Recorder. Anywhere you go, you can just open the app and measure how much light is around. It’s available only in the US and it’s free.

What we find is a lot of people in regular offices who don’t have access to a window have very little light—somewhere between 100 to 300 lux—which is not sufficient to fully activate this melanopsin. As a result, we might feel a little sleepy, we might feel a little down, little blue, a little depressed. And that’s half the problem.

blue led

We can brighten up the daytime by having bright blue LEDs or stepping outside for at least a half an hour under daylight. You don’t have to look at the sun, because daylight itself is 10,000 lux of light, even on a cloudy day. That’s more than sufficient to activate melanopsin and improve your mood.

But the nighttime is a different story. Our system is designed to have maybe less than 20 lux (candlelight is really 1 to 2 lux of light). A typical home these days can have 100 lux of light. You walk into a grocery store in the US or a corner store in Japan, there can be 1000 lux of light, which is a thousand times more bright than candlelight, almost like daytime.

At nighttime, when we go to the grocery store or drug store, we get slammed with so much light that our melatonin level drops. Our clock gets confused whether it’s morning or evening, and our sleep deteriorates. We cannot get a good night of sleep.

That’s why, if we distill all of this into something very simple that someone can follow, daylight truly is the best way to synchronize our internal clock to outside. And daylight is also the best antidepressant. It’s free, you just have to step outside for 30 minutes during the day. At nighttime, try to avoid bright light for typically two to three hours before going to bed so that you can crank up your natural sleep hormone melatonin and that will help you to go to sleep.

DrMR:  Awesome. That’s a nice summary of some of the principles that we’ve already touched on regarding light.  Completely agree with everything there. I think that’s terrific advice. The other topic, and what I am hoping will be the brunt of our discussion today, is the time-restricted feeding piece.

Time-Restricted Feeding and Why It Matters

I do have some particular questions here, the back end that I want to get to. But for anyone who hasn’t heard of time-restricted feeding, can you get them up to speed on what that means and how you came to discover how important this is?

DrSP:   Yes, so this was, again, a huge discovery in my lab in 2012, almost 7 years ago. The discovery led us to circadian rhythm (which means almost every organ in our body has a clock). Just like your brain has a clock that makes you sleep at a certain time of the night. Once you are asleep, you need seven to eight hours of sleep, then it wakes you up.

Similarly, almost every organ in our body, whether it’s gut, liver, muscle, fat tissue, kidney, any organ that is in them, has a clock. So that means every organ, just like the brain, also needs some downtime, so that it can repair, reset, and rejuvenate for the next day.

A few years ago, starting from 2008, we found that our little mice, when they eat mostly at night—because mice are nocturnal, they are supposed to eat only at night—are pretty healthy and normal.

When mice are given a little unhealthy food, somehow, the calorie-dense diet changes their circadian clock, and they tend to eat whenever they want. So they eat randomly, maybe 50% during the night and 40-50% during the daytime. We saw very simply that when mice are not supposed to eat and they eat anyway, they disrupt the organs that are supposed to sleep.

It’s almost like if you’re a new mom or a new dad and you are waking up five, six times a night, you know how tired you are the next day. Similarly, if the mice are eating randomly throughout day and night, maybe their organs are not getting enough time to restore, to repair, rejuvenate, etc.

We did a simple experiment: we took two identical sets of mice, born to the same parents, in the same room, with the same microbiome, the same exact genes. We gave them the same exact diet and the same number of calories. The only thing that changed between these two groups was that the first group got to eat whenever they wanted to eat the food. We call it ad libitum eating, whenever they wanted. The second group was given the same number of calories from the same food within (in our original experiment) 8 hours total. Every night, the same consistent 8 hours.

We did this experiment initially for 18 weeks, which is roughly 3 to 4 years in human life. Surprisingly, what we found was the first group of mice were completely obese, diabetes, they had cardiovascular disease kind of stuff, fatty liver disease. Anything bad that you can think of that happens with humans, happened with these mice. The second group that ate the same number of calories, same identical food, but ate only within 8 hours, were completely protected from all of this disease.

That came out in 2012, and it was a big breakthrough. Until that time, nutrition scientists and also metabolism scientists believed (and even I still believed) that the quality and quantity of nutrition that we eat is most important to keep us healthy. But after the first discovery, we learned the timing of when we eat is as important as what and how much we eat.

Research on Intermittent Fasting in Humans

DrMR:  These results have been replicated in humans. I believe there have been a handful of studies. Can you tell us a little bit about how you start to take groups of people, change their eating window, and what results that’s leading to?

DrSP:   Yes, after the first paper, it was only prevention, and not treatment. So the first couple of years, from 2012 to 2014, we wanted to really focus on healthy mice. Another question was, is 8 hours a magic number? What if the mice ate 9 hours, 10 hours, 11 or 12?

So we did all these systematic studies. What we found was, yes, actually 8, 9, 10, 11, and even up to 12 hours is good enough for mice. We can also reverse many of the diseases. That was very important, because prevention and treatment are not the same. Something can prevent a disease. For example, washing your hands can keep you from getting sick. But once you are sick, washing your hands will not make you healthy. So we had to test that. That was tested.

But during this time, the popular press and the many health causes took it one step further and started recommending it to humans. And it has been documented in many different ways. People call it intermittent fasting, people call it 8-hour eating, many different ways.

Only after we verified that it is possible to reverse a disease in mice, then we wanted to see when people eat, firstly. Secondly, is it a modifiable behavior? Can people change their eating time? And next, what happens if they do?

There are quite a few studies, as you said. Some initial studies were done in our lab and now many scientists throughout the world have replicated it. Most of these studies fall into two or three different categories. The one study that we did initially was to see when people actually eat.

This was a very interesting thing. When we ask people about eating, people usually responded saying they eat three meals a day and many within 10 to 12 hours. We were very discouraged. We thought, wow, if people really eat three meals a day within 12 hours, then our research has no significance.

So we started an app called My Circadian Clock. It’s a research app, it’s free, available both on Android and iOS. People can go to the website called and sign up.


Initially we had very controlled study with 156 people. We asked them to take a picture of everything that they eat or drink. What we find is a lot of people eat or drink something mindlessly and they think that it’s not food. For example, people may eat an apple late into the night, thinking, “Well, this is a healthy snack and it’s small enough it may not count as food.” But we’ve got to remember that whether we eat a big meal or a little apple, our stomach has to process it, send it to the liver. The whole village wakes to process the apple.

When we asked people to record this way—what they are eating, when they are eating—what we found is that nearly 50% of adults in the US (who are not night-shift workers) eat for 15 hours or longer. That means there is a window of 15 hours when they are most likely to eat. 90% of the time in a week they are more likely to eat within that interval.

We know that if mice eat like that, then they become obese. Then we took a small group of people who used to eat for 14 hours or longer, and asked them, can you try to eat within 10 hours? And 10 is kind of an easy entry point to this time-restricted eating or intermittent fasting, because most people can try to do it.

When they did it, we found within 16 weeks they lost 3 to 4 percent of their body weight. It was mostly body fat. They were overweight people, but they were not obese. They didn’t have any disease (you don’t want to try something new on people with a disease).

That was very exciting. Another exciting fact was, people who did this said they slept much better and felt more energetic throughout the day. So they boosted their energy during the day, they slept very nicely at night.

Some of them who had acid reflux said the acid reflux reduced or went away. These are the beneficial side effects that kept them going.

That was the first paper that came out in 2015. Since then, there are a bunch of papers that have come out where people have done modification of this time-restricted eating. People have gone down to four hours for four days, then maybe six hours, then eight hours. Invariably, in all of these studies—and I must say that most of these studies are relatively small sample studies, only 20, 25 people max—people do improve their health. In addition to sleeping well, feeling more energetic, they actually feel less hungry at nighttime. Many markers of disease—for example, blood sugar levels, blood cholesterol level, triglyceride levels—tend to normalize.

Having said that, I’m sure that this year there will be many more papers coming out. But we are still far away from the gold standard study, the randomized control trial in a large number of people, to see whether it has a long-term impact on reversing or better managing some of the chronic diseases.

Sponsored Resources

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Intermittent Fasting and Lowering Disease

DrMR:  Is there a body of epidemiological data that can help draw us an inference? I don’t think I’ve seen anything that’s looked at time-feeding windows in certain populations and correlated that with health or disease. But I also can’t say that I have looked. Is there anything there?

DrSP:   Well, before our study, people didn’t think about the time window. What people have thought about is late night eating or skipping breakfast, because those ones indirectly led to time window. Because somebody that is eating late into the night is likely to have a longer time window.

In that context, there are quite a few epidemiological studies. Some of them are very strong. One is from my neighboring institute, University of California, San Diego, done by Luke Patterson and colleagues, where they looked at women who used to eat an early dinner so they could have 13 hours of overnight fasting.

They found women who fast for 13 hours, or eat within 11 hours all their calories, are less likely to have breast cancer. Then they went back and asked, among women who already had breast cancer, who was more likely to relapse. Again they found that women who eat within 11 hours or less are less likely see the relapse of breast cancer.

There are also other studies. People always immediately ask, “Well, in Spain everybody eats late. What about them? And in fact, last year there was a nice epidemiological study, both men and women in Spain, who had their dinner before 9:00 PM. In Spain, having dinner before 9:00 is almost equivalent to having dinner before 7:00 in the US. So in Spain, people who ate early also had up to 25% reduction in risk for breast cancer and prostate cancer. And that was very profound, because it was the first time we saw a reduction in cancer risk for both male and female.

So we haven’t seen other epidemiological studies yet that strongly connect risk for obesity, diabetes, cardiovascular disease with time window, but I think the concept is so new that I’m sure some epidemiologists are currently looking into it.

retinal blindness

DrMR:  What a powerful but simple measure to help prevent an array of diseases, tending to your light exposure and to your feeding window. I also recall reading a study, years ago now, that showed that women with retinal blindness had a decreased incidence of breast cancer. The researchers posited that this was because even if they were being exposed to light at night, they weren’t able to perceive it and it wasn’t able to affect their hormonal signaling. That hasn’t been really corroborated, I don’t think, but it’s an interesting observation, nonetheless.

DrSP:   Yeah, that is an interesting observation. Although we know that some of those women may still have melanopsin, may be sensing light, at the same time, sensing light and seeing are very different. Light is an enabler. When there is light, then we tend to wake up. And if we are awake, we are more likely to engage in some activity that requires visual function. That means if we are awake, we are working on our computer, watching TV, texting, or doing something else that requires vision.

So I will be curious to go back and see whether these blind women—who didn’t have image-powering vision (that’s what we call it)—may be actually sleeping more because even though there’s light, there is not much stuff to do for people with compromised vision. We know that sleep is also therapeutic. It’s a very strong behavior to reduce your risk for cancer. Even people who are going through cancer treatment… if they sleep better, then their prognosis is much better.

DrMR:  With these studies, obviously one question that comes up is, is some of this beneficial effect imparted by the fact that people may be eating less? I’m assuming that’s controlled for in some of these studies, but what does that issue look like?

DrSP:   As for all of our animal studies, we control calories. All the time-restricted group and ad libitum group eat the same number of calories. So that’s why this has been such a new profound basic science discovery.

In humans, last year Dr. Courtney Peterson, from the University of Alabama, Birmingham, did a very carefully controlled study where she had the same number of calories given to two groups of patients. One group got to eat it within six hours, a very restricted time window. Then the other group ate it within 12 hours.

Even after controlling for calories, she found that people who ate the same number of calories within six hours had much better improvement in cardio-metabolic risk factors. For example, the blood pressure normalized and they had a slight reduction in lipids.

Again, these were not metabolic syndrome patients. They were at risk for some of the disease. So you wouldn’t expect a bigger difference, but still it was very encouraging to see that even after controlling for calories, time restriction had a significantly better impact.

Optimal Fasting Time Window

DrMR:  Very interesting. Okay. So this leads to one burning question that I have. I would say some of the most widely adopted methods for implementing intermittent fasting (if you want to call it that) are to skip breakfast and to push your meals to later in the day. Personally, as I have tinkered with this, I have noticed when I do that, I tend to just backload my meals into the end of the day.

I’ve heard varying things. Essentially I haven’t got a straight read: is it just having a window of fasting, or is it more important to make sure that window falls within a certain time and you are essentially not eating past a certain threshold in the evening?

DrSP:   There are two questions. One is, in the pursuit of perfection, should we ignore what is good enough for us?

Say if someone has a lifestyle where eating dinner with friends or family is the most important thing and giving up that one takes away all the joy of life. Then I think it’s better to skip breakfast and tend to go towards dinner.

But having said that, knowing the biology of circadian rhythm, and how our organs function, our insulin sensitivity is much better in the first half of the day. That means having a bigger meal in the first half of the day, whether you call it a late breakfast or something like that, is a good thing.

Second, the flip side of the coin is, just like our brain goes to sleep, our pancreas also goes to sleep at night. That means almost two to three hours before we go to bed, as our melatonin level begins to rise, it can slow down the function of pancreas, so our pancreas doesn’t produce enough insulin. As a result, if someone is eating up to bedtime, there is a risk that he or she may have slightly higher level of glucose after eating the last dinner.

As we know, again, just like our brain sleeps, our stomach sleeps. Our intestines also sleep, so they don’t process the food as well in the night as they do during the daytime. So a person with a too late dinnertime also stresses these organs. They may not repair, reset, and recover well overnight.

These are some of the biology insights that tell us that it is much better to have an early dinner. Maybe you can delay your breakfast and stick to the 10 to 11 hours. That is a good window for a lot of people to adopt this.

DrMR:  And how late do you feel is too late?

DrSP:   Well, it all depends.

DrMR:  Relative to one’s bedtime, I’m assuming, is how we have to measure that.

DrSP:   As related to bedtime, the rule of thumb is, try not to eat 2 to 3 hours before your habitual bedtime. Even if you eat 3 hours before your bedtime, your blood sugar level will go up and it will stay up for say for 45 minutes to an hour before they come down again.

That means during one to one and a half hours, you want your pancreas to produce enough insulin to control that glucose pretty well. So two to three hours before bedtime should be the time when the kitchen closes and one should stop eating.

Another risk, just like you said, is when people skip their breakfast and have a late dinner, they are also more likely to consume more alcohol and dessert and all this stuff. So in that way, by adopting a late time-restricted eating, one is also at a slightly higher risk for consuming extra alcohol and processed sugar, processed food.

DrMR:  Now regarding a fasting window—and I’m sure there’s probably variation here—are you of the belief that you should have at least an eight-hour fasting window?

DrSP:   Eight-hour eating window.

DrMR:  So you want to have an eight hours eating window and–

DrSP:   16 hours of fasting.

DrMR:  So is there some wiggle room there? Would you say, if you go over the threshold of a 10-hour eating window, you’re really seeing a drop-off? Or is there a little nuance there that you want to color in?

DrSP:   This is where again, the quality of nutrition and length of your eating window interact. That’s what we see even in mice. The mice that eat a healthy chow can tolerate a wider eating window and can be healthy. Whereas mice that eat a unhealthy calorie-dense diet have to stick to a narrower eating window of maybe up to 12 hours, but I would say 10 is much better.

This is where, again, your personal goal comes into play. If someone is trying to lose weight or is trying to control blood pressure or blood sugar, then it may be better to start with a 10-hour eating window. 10 hours eating, 14 hours fasting. Once they have achieved their goal, it may be okay to relax it to 11 or even 12 hours with a healthy diet.

For example, what we see is a lot of people will start at 10 and stay at 10. Or they maybe even shrink that to eight hours eating. We rarely see average people shrinking that too much to six hours or four hours. But there are a few, I’ve heard, who do that.

blood pressure

But on the other side, we also see people who attain their goal of reversing prediabetes or maybe normalizing their blood pressure. And then during this time, one unintended bonus that we see of time-restricted eating (we don’t understand what the biology is) is people reduce their sugar threshold, so they cannot eat too much sugary food. And some people say they also cannot drink too much, so they reduce their alcohol threshold.

As a result, when we reduce our sugar intake and alcohol intake, we also improve our nutrition. In that way, after trying ten hours time-restricted eating for a few weeks or months, if your nutrition improves, then it’s okay to relax it to 11 hours. Sometimes we see people go up to 12 hours, and they’re still healthy.

So it boils down to, now, a few things. What was your eating window before? Some people habitually eat 16, 17 hours. When they go from 16, 17 to 10 hours that’s a big change, and we’ll see a big impact. For them, even relaxing it to 11 or 12 is not that bad. And some who are currently eating within 12 to 14 hours, if they shrink it to 10 hours, it may be a modest change and maybe staying at 10 hours is a good thing.

Building an Intermittent Fasting Habit

DrMR:  Are you finding that people need to be built up to this? Meaning, if they’ve been eating over a 16-hour window, is it hard for people to go all the way down to eight? Or do people tend to respond really well and they can just jump right to it?

DrSP:   There are a lot of factors. For people who are doing an eight-hour job and their commute time is one hour each way, it becomes very difficult for them to jump into an eight-hour eating window unless they sacrifice eating at least one meal with their family. So in most cases, for the average Joe, what we find is the current commitment to work, life, etc. are the biggest barrier to adopt a shorter time window. But many of them can adopt a 10- to 12-hour eating window.

DrMR:  Okay. So you don’t find that there’s a need to work people up to this? Do people seem to—lifestyle factors aside—from a biological perspective, try to abate cravings or any funky adjustment?

DrSP:   The first week is a little bit difficult. But if we warn them, this is what you are going to expect, you may feel a little hunger pang at dinnertime in the first week, then they’re prepared. They know that this is what they’re expecting, it’s not going to kill them. They go over that first week, then they’re fine from second or third week onwards. They don’t actually feel hungry at all at bedtime.

DrMR:  Just to clarify for people… let’s say they’re starting to incorporate this into their lifestyle and they’re having a feeding window on average of maybe around 8 to 10 hours, and have an occasional deviation. I’m assuming that doesn’t really pose any problem. It’s just looking at what you’re doing the majority of the time and not getting too worried about the occasional excursion from that. Is that correct?

DrSP:   Yeah, that’s correct. But at the same time, people have to be very objective in that “occasional deviation.” Many times people say that, I typically eat within 10 hours. And then if we polled them a little bit more, then we realize that okay, three to four times a week, they are going outside this window. And that’s not really good. It all depends on what kind of deviations they have, but in general that’s not good.

In animal experiments, we have tested this objectively. In animal experiments, we let them two days free in a week, so two out of seven days. The other five days they ate within 9 to 10 hours (not 11), and they seemed to do okay. They’re better than eating randomly. They’re not as perfect as mice that eat 9 hours every day, but they are still reaping maybe 80% of the benefits. So up to two days in a week is okay. But beyond two days is not.

DrMR:  I’ll second the observation that people tend to have wishful recall. Now, will that app, My Circadian Clock, help people with this?

diet schedule

DrSP:   Yeah. So actually, this is interesting, I just had a conversation with some primary care physicians who had stumbled on the app, and have been trying to tell patients that they should pay attention to the timing of eating. The patient will say, “Well, I eat within 10 to 12 hours, or I’m trying,” they don’t see any improvement.

Then they’re asked to use the app. Once people are used to logging their food and checking what time they are actually eating, that changes their behavior. That helps them to stick to it for a few weeks. Once they stick to this for 10 to 12 weeks, then they will see a measurable effect, a medically-significant improvement. Sometimes some blood pressure, sometimes some blood sugar. And sleep quality, for example, improves very quickly within a couple of weeks.

So this is some of the stuff that we’re hearing from our physician colleagues, who have been prescribing or advising their patients. So the app actually helps. It’s almost like you’re trying to comb your hair without a mirror. It’s difficult. But if you have a mirror, and you can see yourself and what you are doing, it’s much easier to correct what is wrong.

DrMR:  In the app, is the way the user tracks this that they just snap a photo and it logs the time for them? Is that how this connects?

DrSP:   Yeah, so you can snap a photo. Or if you’re in a meeting somewhere, or if you forgot, you can also just manually enter, “I ate…” Some people are very descriptive, they’ll write every single thing that they ate. Some people will say, “I had lunch” or “dinner” or “breakfast,” and the app actually remembers your entries so it will auto-suggest. It’s a very simple app, but it seems to have a very profound effect.

In fact now, we’re using the same app, in a slightly modified version, in many controlled clinical studies, so we can refine the backend and also interact with the patients who are specific to the studies. We’re finding that once people start logging what they’re eating, when they’re eating, that helps them stick to the habit for a long period of time.

DrMR:  Sure, yeah. The first step oftentimes is awareness, so that would make complete sense.

When to Expect Results with Intermittent Fasting

The other question I wanted to ask you, you just alluded to, but I wanted to make sure I have a really clear understanding of this. Especially for maybe somewhat healthy populations who are looking to just optimize, maybe sleep a little bit better, lose a couple pounds… how long until someone sees results?

It doesn’t have to be the full result, but one of the things I find is helpful when giving someone a recommendation is, “Okay , it’s going to take about X length of time until you can expect to see things. So be patient until then, and then we can re-evaluate.”

DrSP:   Yes, if someone is already eating for 15 to 16 hours and they are trying to go to 8 to 10 hours, of course the first week will be difficult. But in the second week almost, one may experience an improvement in sleep. So that comes pretty quickly, by the second or third week.

If it is weight loss, of course, initially there’ll be some drop in weight because of glycogen storage and water loss, etc. And then the weight loss is gradual. It may take 10 to 12 weeks to see a gradual weight loss. It will not be a very active weight loss, but if they continue with the habit, then even up to a year, I’ve had some people losing modestly, to people losing really big numbers, up to 70 to 80 pounds. Of course, they started with a very large number, but it’s gradual. It’s not like what you see on TV and other advertisements, that you lose 10 pounds in 10 days. It’s not like that.

Imagine, we have accumulated this body weight over many years. And if we tend to drop very quickly then the body will resist and gain back that weight. So maybe in 6 to 10 weeks, somebody will see a significant drop in weight. But if they continue with it, then they will see much more improvement up to 6 months or a year.

When it comes to blood pressure and blood sugar, some studies have shown that the blood sugar actually improves even within 6 to 10 weeks. I would say one may wait up to three months/twelve weeks to see some improvement in blood sugar. And then with blood pressure, the same thing, because Courtney Peterson’s study also showed, within a few weeks, they experienced an improvement in blood pressure.

So three months is a good timeframe to give to your patients.

DrMR:  Okay, fair enough and that makes sense. Now, one of the things that I noticed—and this is more a question I’m asking for the clinicians listening to this—sometimes you deal with a patient that’s burnt out, dependent upon stimulants, doesn’t do well with fasting, doesn’t sleep well, might even be underweight. I’m sure you’ve heard these people describe this as unstable blood sugar and they’ll have these crashes if they don’t eat frequently. Are there any modifications you’re making for this population?

DrSP:   Yeah, unfortunately, we haven’t looked at that population. Some of our ongoing clinical trials are very well-defined for certain populations and we haven’t done anything for this very unstable population.

DrMR:  All right, well, I can only ask you so much right?

DrSP:   And I’ve got to be very honest. As a scientist we have to know our boundaries, what we are doing, and how far we can go.

DrMR:  Yeah, could not agree more on that point.

View Dr. Ruscio’s Additional Resources

We’ve covered a lot of fantastic ground. I know you have a book and website. Will you tell people about your book and where they can find that? And anything on your website that you want to direct them to, and any other resources you want to point them towards?

The Circadian Code

DrSP:   Yeah, so I wrote a book last year. It’s called The Circadian Code, it’s now available on all major websites. Amazon carries it. I wrote the book because the science of circadian rhythm is very new. Most of the key discoveries in this field were done only in the last 10 to 15 years. So that means most of the key discoveries have not made it to textbooks for physicians, nurse practitioners, or anyone who comes in contact with health care delivery.

The Circadian Code

So that was the incentive for writing the book. It’s written in a language that’s accessible to both lay audiences and also curious educated audiences like physicians and other scientists.

It begins with the concept of the circadian clock and then the best example of the circadian clock in everyday life is when you think about shift workers who work the night shift or swing shift, etc. I argue that almost all of our lifestyles are like shift workers, because we do disrupt our sleep many times within a year. That has a very bad effect on our body.

Then I go on: what is circadian rhythm, and how to track and test your circadian rhythm. And there are tips for how to get a good night’s sleep, because sleep is a big aspect of circadian rhythm.

Then we go to time-restricted eating, when to eat and then also when to exercise. Recently, Julien Girard, who is a very well-respected diabetes scientist in Stockholm, just published a paper showing if people with type two diabetes exercise in the evening, they can much better control their blood glucose than if they exercise in the morning. So the timing of exercise has a huge effect.

DrMR:  Does that exercise bit apply globally? Do you see, across the board, better benefits from exercise when it’s done in the evening as compared to the morning, or is that more so in a specific population?

DrSP:   That was known for a very long time for the general population. For example, even well-trained athletes’ athletic performance is much better in the late afternoon to early evening, somewhere between 5 pm to 8 pm. It is so important that, historically, people have looked at athletic teams flying from the West Coast to the East Coast and then playing, say, pro football. If they flew on Saturday or Sunday, they found that the West Coast team playing on the East Coast had a much better chance of winning against the home team on Monday night. But the advantage goes away with Tuesday, Wednesday, Thursday, because on Monday they’re on West Coast time so they perform very well. So there is a long rich literature on athletic performance and timing, and I also go into that literature in this chapter.

And then finally, part three is about how to use the knowledge of circadian rhythm to improve your digestive concerns. So this is something that we didn’t have time to talk about, but we do see a huge, huge impact on digestive diseases from having time-restricted eating. Then, for fixing metabolic syndrome, obesity, diabetes, and heart disease, I discuss how we can use the science of circadian rhythm to improve these conditions, maybe prevent, or reverse sometimes. And the impact of circadian rhythm on the immune system, autoimmune disease, inflammation, and even cancer.

Finally, it covers how to use the science of circadian rhythm to reduce the severity of some mood disorders, whether they’re depression, bipolar, ADHD, or AST. Most of these chapters have the citation to the original research work that is discussed here. People who are more curious can also go from the chapter to the original paper.

Digestive Benefits from Intermittent Fasting

DrMR:  I love that. I want to be respectful of your time. This is my last question, but my audience will kill me if I don’t ask for at least a short comment on the digestive benefits from intermittent fasting.

DrSP:   Yes. So just like our brain, our digestive system also sleeps. What happens is, between 8 and 10 at night—for a regular person who goes to bed, say, around 10:00—our stomach is most sensitive to food. So that means if we eat at that time, our stomach produces more acids than if that same food is given during the daytime. That means those who are at a high risk for acid reflux should not eat after 8:00 or 9:00. You can reduce the incidence of acid reflux, or maybe the severity acid reflux, by avoiding food late into the night.

Second, our intestine slows down. So even if you eat, it doesn’t get digested, because the intestine doesn’t pump that food from the stomach down the intestine. As a result, you might get indigestion. The same way you cannot repair a highway when traffic is still flowing, similarly, when there is food in the stomach, the intestine then cannot repair our gut lining.

This is very important. Every single night we have to replace nearly 8 to 15% of our gut lining, because it gets damaged with the digestive process. If we don’t repair it, then slowly we may have leaky gut of the disease-causing bacteria, or maybe allergy-causing food particles can leak out into circulation and can cause autoimmune disease, food allergies, etc.

Time-restricted eating allows our gut to go through 12 to 16 hours of fasting, 12 to 16 hours of downtime when the gut can repair itself. So in that way, this time-restricted eating or intermittent fasting also has the potential to improve gut health and we do see that in many of our patients.

Episode Wrap-Up

DrMR:  Fantastic. And I will second that. Intermittent fasting is very helpful for a number of patients and definitely something, if you’re listening to or reading this, to consider incorporating into your gut health optimization plan.

Satchin, this has been a fantastic call. Thank you so much for taking the time and also for doing the research you’re doing. I think it’s helping to obviously increase awareness about how it’s not just what you eat but when you eat. So again, very appreciative and thank you so much for your time.

DrSP:   Thanks a lot.

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