Understanding Fasting

Let’s talk about what fasting is; simply put, it is not eating, and there are lots of times when we’re not eating. For example, when we’re sleeping, we’re not eating, and that’s also called fasting. Now, when you wake up in the morning after a night’s sleep and break your fast, you’re having breakfast. And that’s as simple as it gets; we’re naturally fasting every single day.

When we’re asleep, and then we break our fast whenever we eat, it might be breakfast; if you skip breakfast, it might be lunch, and you might have an early lunch, and that is as simple as it gets now. There are ways of actually extending fasting and practicing fasting to be able to make your body do more during this fasting time, and I’m going to explain all that, but I want to take you back into history a little bit.

Fasting Through History

Many cultures and religions routinely practice fasting. For example, when I was on a gap year before I went to medical school, I traveled to the Mediterranean, and one of the interesting experiences I had was going to Mount Athos, which is this Holy Mountain in Northeast Greece. It is a series of monasteries built into the rock of this mountain, and I was doing some mountain climbing, hiking, and research on the livelihood and the health of the people that lived in this monastic community.

They live a 16th-century lifestyle, and that’s what fascinated me; to look at what it would be like to live during medieval times. So that was like going to the time machine and coming out in the 16th century, for example—the monks in the Eastern Orthodox religion practice routine fasting. So fasting isn’t just a modern trend; it’s something that’s been around for a long time.

Daily Fasting

Fasting is also very natural; we do it every single day while we’re not eating. Now, let me extend this idea of fasting, not eating, to an extreme. If you were shipwrecked on a desert island and you didn’t have food, or if your car broke down in the desert and you had to walk through a parched desert environment for miles and miles and there was no food, eventually you would be not eating for not just hours but for days. That’s also a kind of fasting; eventually, you’ll start to consume your own body because your body is looking for energy.

That fasting becomes starvation, and obviously, you’ve seen pictures of people in concentration camps and in other extreme circumstances where they become skeletal. They have almost no muscle or fat left in their body because they’ve been starving, and that’s an extreme of fasting. So that’s important to understand as well: if you’re in a desert and you don’t eat for days and days, your body will consume itself, and that’s an extreme of fasting.

How Overeating Overloads Your Metabolism

Let’s talk about not fasting to understand the opposite end of fasting. So you’re eating, you’re eating all the time; in fact, you’re overeating, and this is one of the big problems in many modern societies because we are surrounded by an abundance of food and we are marketed food all the time. We always have it in front of us, so it’s easy to snack on things.

Then, when we’re eating, we’re not eating mindfully; we’re busy, and when we’re overeating, we overload our metabolism. That’s the opposite of fasting, and when we’re eating, what happens is that our body, our pancreas, produces insulin, and insulin comes out whenever we are eating to be able to draw the fuel from the food that we just ate. This is put into our muscles and our storage systems, the fuel tanks in our body, that’s our body fat, so we have enough energy.

Insulin’s Role: What Happens When You Eat Too Much?

If you eat regularly, your insulin will go up, and it’ll take your blood glucose down to normal levels. Then, you wait for your next meal, and your glucose goes up. The fuel goes up, the insulin comes out, draws it back, and your insulin and your glucose levels go back down. That’s basically how our body, the central part of our metabolism, works when it comes to eating and hormones like insulin.

I’m not going to go any deeper than that for the moment, but what happens if you overeat and continuously put fuel in your body? It’s like taking your car to a gas station and filling up the tank, but rather than stopping and pulling the nozzle out when the clicker goes on, your tank is full; you just keep forcing more fuel into your tank. Now, in your car, the fuel tank is made out of metal, so it’ll just overflow, but in our body, when we overflow our fuel tank by adding too much fuel, meaning overeating, what we’re doing is we’re able to stretch our fuel tanks. That’s our fat cells. You keep stretching the next one and the next one, and you can make a single fat cell expand three times its size (300%). Then, you can make more fat cells when you need more fuel because you’re eating more, overfilling your tank, so to speak.

The Effects of Excess Fuel on Your Body

The fat fuel tank goes up and gets bigger, and this is exactly what we’re seeing. This obesity epidemic is between fasting normally and overeating and then putting our metabolism through a lot of stress because we’ve got too much fuel in our bodies. Then you’re stretching out your fat cells, and that becomes obesity. All the bad things you can imagine that happen in your body when you’ve got too much fat; too much fuel, becomes inflammatory and takes down your health.

Your whole health systems get derailed. I talk about your health systems in my book Eat to Beat Disease and metabolism and body fat in Eat to Beat Your Diet, my second book. So, if you want to get much more detailed, I’d recommend you read those books because I explain that in great detail.

Overeating overwhelms your metabolism; when you’ve got too much fuel, you’ll also cause a lot of insulin to come out. Insulin is trying to draw that fuel into your muscles and fat stores. When you have too much insulin, one of the things that happens is that your body needs to make more insulin. Then, it keeps making more insulin because it needs more and more insulin.

Therefore, you have a lot of something called the insulin-like growth factor (IGF) produced in your body. This insulin-like growth factor in normal amounts is perfectly healthy, but when there’s too much insulin-like growth factor – that’s a setup for a lot of dangerous situations, including metabolic problems and even cancer. An excess of IGF stimulates cancer- this has been shown in the laboratory, and it’s been correlated in the clinic. This is one of the reasons we think that overeating metabolic syndrome, overweight, and obesity are tagged in part to the whole idea of cancer.

Now, the other thing when you grow a lot of fat is that fat as a fat expands, it’s outstripping its blood supply, and when that happens, inflammation sets in. Now you’ve got inflammatory fat, and your body suffers from the consequences of inflammation. All this overeating and obesity to starvation are two extremes, and somewhere in the middle is exactly where we want to be.

Natural Fasting & Why It’s Good for You

Natural fasting is also beneficial, and we’ll talk about its benefits. What’s happening when we’re not eating? A great way to ask this is: What happens when we’re sleeping? Well, number one is that when we’re not eating for a prolonged period, our insulin levels go down because there’s no more fuel in the body to bring to our muscles, our fat stores. When our insulin goes down, our metabolism shifts gears. I refer to this like shifting gears in a race car, and it goes from fat-storing mode to fat-burning mode. When you’re fat-burning fat is actually when you’re fasting. That’s when you’re sleeping. Many people don’t realize this, but we burn fat when sleeping. When we don’t even need to exercise to burn fat, that’s part of our body’s natural metabolism, and that’s also the reason why you want to fast for a reasonable amount of time every night.

What’s a reasonable amount of time? On average, sleeping 7 to 9 hours in the evening is a reasonable amount of time. Eight hours is a good amount of time to sleep. Sleeping is restorative to our brain, metabolism, gut microbiome, and immune system. Sleeping is vital for us, and one of the reasons it is essential is that it gives us this fasting window.

Let’s call it eight hours of fasting, eight hours of sleep where our body is shifted into the mode to burn down extra fat stores. That’s beneficial because whatever calories you’ve loaded into your body during the day, you get to burn some of them off in the evening. When this occurs, you shift into a state where your insulin levels are low since you’re not putting fuel into your body. Your body shifts into gear.

Cool Sleep, Hot Metabolism: The Power of Brown Fat

Now, the other thing that should happen is, when you’re sleeping at night, you should sleep in a cool room, like 67° or 68° degrees Fahrenheit. The reason is that we get more benefits from cooler temperatures. Brown fat is a healthy fat in our body, and it’s not wiggly jiggly like the muffin top of the fat in your thighs; it’s more like the thin fat around the side of your neck, behind your breastbone, and between your shoulder blades. One of the things that can happen is that at cooler temperatures, our brown fat switches on; it’s like turning on the gas jets on your stovetop.

To turn on the gas on your stovetop, you need the flame to draw gas fuel from someplace. It could be a gas propane tank on the side of your house or from the town’s gas lines. But in your body, when your brown fat turns on, it’s a process called thermogenesis. It triggers on the generation of heat it has to draw that fuel from.

Brown fat, good fat, draws extra fuel from your white fat, which can be bad fat if you have too much of it, particularly in the tube of your body called the visceral fat. This happens at cooler temperatures, so when you’re sleeping and fasting, if you turn down the temperature, you’re improving your metabolism because you’re turning on thermogenesis.

White fat is that inflammatory fat that builds up. Build-ups can expand and become inflammatory and cause all these problems. Brown fat is a good fat, and it is activated when you have a cool temperature. When you are burning down that extra body fat that you don’t need, your inflammation starts to taper off. This isn’t just on an hour-to-hour basis or even one evening basis. This happens over time, and this is why you want to practice regular fasting, which we all do when we’re sleeping. You should be conscious of it and mindful of the fact that when you get a good night’s sleep, you’re doing something good for your metabolism by burning off extra body fat.

Intermittent Fasting: What’s the Buzz All About?

Where does this new trend of intermittent fasting come from? It sounds like a brand-new diet trend, and everybody’s getting into it. You have to fast for 16 hours and eat for only 8 hours. Think about what eating only 8 hours a day would be like. Getting up in the morning at eight and eating breakfast, then if you wanted to have everything squeezed into 8 hours, you have to eat dinner before 4, and that’s your 8-hour window.

A lot of people do that; it’s a practice that works because if you’re not eating for 16 hours, your body is shifted into that fat-burning mode. You’re going to lose weight because you’re going to burn down extra fuel and a lot of extra calories, which can benefit your body. For most people that I know, and probably you as well, practicing eating within an 8-hour window is a tall order because it doesn’t fit into most people’s schedules. If you’re cooking for a family, if you’ve got kids, if you’ve got a regular day job where you need to dine out, it’s very difficult to squeeze everything into an 8-hour window. If you can do it, more power to you, but the whole point of healthy fasting and the overall diet lifestyle is to do something you can sustain regularly throughout your lifetime. It’s tough for most people to do over the course of their lives, so I want to explain how to do fasting in a more common sense way.

Balancing Fasting with Real Life: A Practical Approach

First of all, I want to recap what works. You know, 16 and 8, 16 hours of fasting and 8 hours of eating isn’t some magic number. It works clinically, and it works for some people, but it isn’t a magic number that was studied in huge clinical trials. Medical scientists pulled out, “You have to fast for 16 hours”, but it’s not a hard-fast rule; any fasting works. The idea came from a publication on lab animals, which was somewhat arbitrary from a researcher. It does work for some people, but again, it’s not that practical, and then during those 16 hours of fasting, your metabolism shifts into fat-burning mode. You’re burning down extra calories, lowering inflammation, losing visceral fat, and losing body weight.

Debunking the 16-Hour Fasting Myth

It’s good for you in many ways, but it’s not practical. You should know that research shows that not only 16 hours of fasting and 8 hours of eating work. Even 12 hours of fasting and 12 hours of eating is a much more reasonable time frame and is a decent way of fasting. You can lose weight and body fat, and you can also improve your metabolism. That’s a pretty reasonable way to operate.

Before we talk about 12 hours of fasting and 12 hours of eating, which is the more reasonable way of doing it I want to talk about the situations where people do fast from a medical perspective for long periods. Sixteen hours and even more, maybe even fasting for a day or two. What happens when you fast for a long time before you go into starvation? Your body starts to generate its own energy. So you’re not putting fuel into your body, and your body eventually senses this and goes into a panic mode. It goes okay now; we need a new plan to get some energy. Your body will then produce ketones. Ketones are an alternative energy source, but your body can’t produce them forever. This is when you start digesting your own body; during this period, you’re producing ketones as a fuel source, and your brain uses ketones.

For example, it’s been found by medical researchers that it can help treat seizure disorders in epilepsy.

It’s also been studied because it affects the brain and has also been used as a metabolic intervention to treat brain cancers like glioblastoma. There’s some evidence showing that fasting and ketogenesis with the generation of ketones can be helpful and useful, and there’s an active area of research.

12-Hour Fasting: A Practical Approach

Let’s talk about how to do it in a window that’s quite reasonable to do. So, 12 hours of fasting and 12 hours of eating. You can do that very easily, and I’ll tell you how I do. If I am getting up at 7 a.m., for example, eating breakfast at eight and having my regular day. I eat dinner around 7 in the evening most of the time. When I eat dinner, it lasts about an hour, and most people are about the same. I know that there are many places around the world where people enjoy hour-long dinners. That’s a privilege, and usually, if you’re eating with other people, that’s also a healthy thing to do. Let’s say that I eat dinner at seven, and I put my dishes away at 8. I’m done right now, and I don’t eat again until the next day. I don’t do midnight snacking and I don’t grab one last thing before I go to bed.

For this example, let’s say that I go to bed at 11; I usually go to bed a little bit later, but let’s say, for the sake of this argument, that I’m going to bed at 11. I should try to sleep for 8 hours, so I’m going to bed at 11. I want to sleep until 7 in the morning. That’s a reasonable amount of time, and it’s not too late to go to bed, and it’s not too early to rise.

Eleven to seven is my sleeping time, and during those 8 hours, a lot of things are happening in my body that’s good. Remember when I explained this to you: I’m eating dinner at 7. I finished eating, and I put the dishes away at eight. The fuel in my bloodstream goes up after I eat the food. My insulin levels are going up to draw that energy down into my body, into my muscles and into my fuel tanks, my fat cells. I’m not eating after I put the dishes away, and so, eventually, my fuel levels and my glucose will go down. The insulin levels will go down, and my body will sense that. Let’s switch to fuel-burning mode since we won’t be loading up. We won’t be storing fuel anymore; let’s just burn it down. So between 8 and 11, when I go to bed, it’s about 3 hours of time where I’m fasting. I’m starting my fast. Then from 11 to 7 in the morning, that’s another 8 hours, so that’s 3 hours before bedtime, and then another 8 hours during. That’s 11 hours from 11 to 7, so 11 hours of fasting.

At that time, my body switched to fuel-burning mode. I’m burning down extra calories, extra fuel that stored my fat. I’m helping to streamline my metabolism simultaneously, and many other good things are happening while I’m sleeping. My brain is being detoxified, my gut microbiome is rebooting, my immune system is actually being reset, and I’m improving my metabolism.

Morning Routine: Extend Your Fast Naturally

So it’s 7 in the morning. I’ve had 11 hours of metabolic improvement. I don’t eat breakfast right away when I get up in the morning. This is a Pro tip for you if you want to extend your fasting window rather than do what you did as a kid. When your mom said, “hey, roll out of bed, eat some breakfast, and don’t miss the school bus,”. Many of us have this pattern; we’ve been trained to eat right away when we get up. I’m going to tell you to take it easy on yourself. Get up in the morning. You’re an adult; get ready and take your time getting ready. Brush your teeth, take a shower, get dressed, and then, if you’re like me, take a little time before you eat.

You don’t need to rush into breakfast right away; you might feel hungry, but most of our early morning eating is coming out of a habit more than anything else. Don’t worry. You’re going to survive if you don’t eat something right away.

I check my email; I might read, catch up on the news, and see what happened overnight. I might read a few pages of a book or open the door and step outside to get some fresh air. It’s good to do a little stretching and all those natural things you would do. Before I know it, between the time I get up and the time I might eat breakfast, let’s say at 8, I got up at 7, and I waited for an hour; it’s eight now. I’ve added an extra hour to my fasting.

So, I put the dishes away at 8: 3 hours to 11:00. I’m going to bed from 11:00 to 7:00 in the morning, so that’s another 8 hours. That’s 3 + 8 is 11: now I put an extra hour between 7 and 8:00 a.m., and now 11 + 1 is 12. I’ve fasted 12 hours out of 24 hours, and I have fasted half of the day. I put my metabolism into fat-burning mode 12 hours out of 24, 50% of the day.

You should know that drinking coffee or tea, as long as you don’t put sugar or milk in, doesn’t break your fast. It’s just liquid, and there’s some bioactives in it, but they don’t count as calories. I almost always have coffee in the morning.

Let’s say you’re getting up at 7 in the morning, that’s 11 hours, and now, if you don’t eat until noon, so 7 to 12, that’s 5 hours, so now that’s 12 plus 11 + 5. Now you’ve got 16 hours of fasting by skipping breakfast, so you can get to 16 hours, and that’s a more reasonable way of doing 16 to 8. What I’m telling you is that you can do 12, and clinical studies have been done to show that it’s actually good for your metabolism as well. That’s my little trick to you: to do the fasting window in the morning. When I’m busy, I sometimes skip breakfast, and I can extend my fast, which is even better.

Avoid Overeating: Balance Your Fasting and Eating

The key thing I want to tell you is no matter how many hours you’re fasting, when you finally do eat, let’s say you eat breakfast after 8 o’clock or skip breakfast and eat lunch; whatever you do, you don’t want to overeat. Remember, we talked about overeating. What overeating does is overload fuel. Put too much fuel in your fuel tank, and you’ll start building up those fat stores again. When you fast too long, you tend to get hungry, and that actually sets you up to overeat.

I’d like to remind people of the idea of not overeating. There’s a Japanese saying from a confusing concept called Hara hachi bun me. Hara hachi bun me means stop eating when you’re 80% full. When you’re satisfied with your meal, you pay attention to how your body feels, and when you feel satisfied that you’ve had your food but are not full, you’re 80% full. So stop and leave the party before it’s over; don’t clean your plate, stop when you’re 80 % full and leave the table. That’s a good rule of thumb so that you’re not overeating after you’re fasting.

Adapting Fasting for Night Shifts

There are a couple of things that you want to look at when you’re looking at time windows. I just gave you a time window during the day that works for most people, and it certainly works for me. Some situations require you to be a little bit more creative.

For example, if you are working a night shift, so whether you’re a security guard, a nurse, a doctor, a fireman, on an overnight shift or graveyard shift, or maybe you’re a policeman. You will be dealing with a completely different mindset, but you can work it out in your head when you are awake and at work when you are eating. When you come home post-shift, you use those eight hours, and then you have an extension on both sides to give you the correct hours.

The key is that if you’re going to eat at work when you come home, don’t eat a ton of food and keep on eating a ton of food. When you’re home, it’s as if you have a day shift job. That way, you’re not disturbing your sleep cycle, your metabolic cycle, or your fasting cycle while you’re at home. During the day, you just have to be able to turn the schedule upside down if you’re doing a night shift. Treat the night shift as a time you’ll be eating, and then when you’re at home, don’t start picking at the food during breakfast, lunch, and dinner hours. Flip it around, and home time will become fasting time.

Managing Fasting and Sleep for Shift Workers

The one thing that’s difficult about the night shift is that sometimes it’s hard to sleep quite as well during the day, so you’re not actually getting good deep sleep. Some people call it REM sleep; it just refers to the type of brain waves that occur when you’re having a really good night’s sleep. You may not be shifting entirely into the metabolic burning mode, so the night shift isn’t the best for metabolic health.That’s why clinical studies have shown that people who work night shifts are more vulnerable to chronic diseases like diabetes, cardiovascular disease, and even cancer. My advice if you work the night shift, and I’ve worked plenty of night shifts as a doctor, is to ask for the day shift when you get a chance.

Fasting on the Go: Tips for Travel

How do you manage to fast when you’re traveling? You’re on vacation or business travel, which is the tough one because you might be crossing time zones. It’s evening when you leave, it’s a bright day when you wake up, and you might not have slept well on the plane.

You might have been fed all the time on your plane or in a hotel, and now you don’t have access to food. You don’t have much control over the food. Vacation is really tough sometimes. What I want to share with you is a rule of thumb about fasting that I learned when I was on Mount Athos. I told you that during my gap year, I spent time in Greece in a northeast section called Mount Athos. I visited to do some research and some rock climbing and mountain climbing. It was an amazing experience.

Anybody who doesn’t know what Mount Athos is you should check it out. It’s a fascinating place to live a 16th-century lifestyle.I remember talking to the monks there, who were pretty hardcore about their fasting regimen when they were in the monasteries. They say when they’re traveling (because I asked them this very question): “What do you do when you’re traveling? How do you handle the fast?” and they said they cut themselves a break when they’re traveling or when they’re sick, and they don’t have to stick to those hard and fast rules for when they’re eating and not eating.

Finding Balance Between Enjoying Travel and Fasting

When traveling during that period, you go from point A to point B. Take it easy on yourself; you can step back from the travel thing and let whatever is going to happen happen. You know what your body does when you’re sleeping and not eating is that you’re switching into a fat-burning mode, which is good, but don’t get too stressed out about it. Try to get back into the program when you get to where you are or when you can return home. Having a more regular program is a great way to handle traveling. I think you know that the joy of traveling is the food. Part of the joy of traveling is to immerse yourself in the environment, so you want to adjust yourself into your new environment as quickly as possible. If this is a vacation and once you’re adjusted, remember that when you’re sleeping, you’re not eating, and when you’re not eating, you’re fasting. The longer you can stretch that out between when you finish your meal the night before and when you eat your first meal the next day (if you can stretch it out to 12 hours), you know that’s a pretty reasonable window to get metabolic health.

I hope you guys learned something about practical tips for fasting and fasting windows.

Other Resources From Dr. Li

MY COURSES

– Eat to Beat Disease
– Elevate Your Metabolism

MY BOOKS

– Eat to Beat Disease
– Eat to Beat Your Diet

STAY CONNECTED

– Website: https://drwilliamli.com/
– Instagram: @drwilliamli
– Facebook: @drwilliamli
– Twitter: @drwilliamli
– TikTok: @drwilliamli