Most of the eating and dietary advice tries to answer what or how much to eat. But did you know that when you eat has massive health benefits for you too? And that it can overcome a great many of the limitations of the other two parts? This is the concept of time-restricted eating: you literally restrict your eating timings to a window that is most aligned with your circadian rhythm.

Did you know: Time-restricted eating is often grouped under the umbrella of intermittent fasting, which describes all types of fasting from a few hours to a few days. The big difference is that time-restricted eating also takes your circadian rhythm into account.

When is the best time to eat based on your circadian rhythm? You eat most aligned with your circadian rhythm if you eat for as few hours as possible (ideally as few as 8h) and as early as possible. This is called (early) time-restricted eating and allows your organs to repair and rejuvenate themselves in a daily state of fasting, which has vital health benefits for your body.

Read on to get a full understanding of:

• Why it matters when you eat and how this determines the state of your organs
• Why time-restricted eating is the way to align with your circadian rhythm
  • For how many hours you should eat every day
  • Why it is better to eat rather early than late
• How you can achieve your optimal new daily eating routine and how you can overcome possible short-term obstacles on the way there
• What the most important health benefits of time-restricted eating are, ranging from 
  • Metabolic health
  • Autophagy
  • Weight Management
  • Glucose, Insulin, and Diabetes (type 2)
• What the most common myths around time-restricted eating are and how to debunk those
• My personal experiences and your key takeaways

To set the right state of mind from the beginning: Not everything that is common and normal now has also been common and normal during most parts of our evolution.^​1​

“The most common eating pattern in modern societies, three meals plus snacks every day, is abnormal from an evolutionary perspective.”

Mark Mattson et al.

And do you know what would be normal from an evolutionary perspective? Living and eating aligned with how we evolved to (and yes, that’s all about your circadian rhythm). But one step at a time…

Time-Restricted Eating (TRE)

Why Time-Restricted Eating Aligns Your Eating Times With Your Circadian Rhythm

Satchin Panda, the leading researcher when it comes to the connection between your circadian rhythm and eating timings. He is the pioneer in the field of time-restricted eating and professor for Regulatory Biology at the famous Salk Institute. And in his book titled “The Circadian Code,” he stated the following about the importance of the time you eat:^​2​

“It’s not only how much we eat and what we eat, but when we eat that matters; especially for long-term positive health outcomes.”

Satchin Panda

This is exactly what we’ll explore here: when you should eat. And why this is all based on your circadian rhythm.

Timing Signals of Food

How Your Circadian Rhythm Optimizes the Timing of Your Digestive Organs

And why does it matter when you eat? Because of your circadian rhythm. In short, your circadian rhythm is your body’s daily rhythm that optimizes the timing of all its functions. And that includes all your digestive organs too.^​2,3​

Think about it from this perspective:

• There are many functions that your body needs to perform every single day, but it cannot perform all of those functions at the same time.
• And some functions only make sense at specific times.

And when you eat influences your circadian rhythm of your organs. Because it determines the state they have to be in.

When you think about your digestive organs now, there is one function that they need to perform. And that is your digestion. But, once they are finished with this, they need to repair and rejuvenate themselves. And this is their daily, circadian rhythm. 

Circadian Phase	Digestion	Repair & Rejuvenation
When does it start?	As soon as you consume any kind of calories.	About 2 to 3 hours after you consumed your last calories.
When does it end?	The digestive processes need about 2 to 3 hours after you consumed your last calories.	As soon as you consume any kind of calories.

It is the first calories that signal the start of the day (the start of your digestion) for your organs. And the absence of calories signals the end of their day (the end of your digestion). And only when your organs don’t have to digest any more calories (about two to three hours after you’ve consumed the last ones) can they work on their repair and rejuvenation.

And giving your organs enough time for their repair and rejuvenation phase – through time-restricted eating – will have health benefits for virtually every part of your body. It allows your organs to optimize the timing of their functions – to follow their circadian rhythm. But with our modern eating patterns, you routinely force your organs to expand their digestion phase. At the expense of their repair and rejuvenation phase, which they then have to cut short.^​2,4​

We’ll go deep into the benefits of aligning your eating times with your circadian rhythm – time-restricted eating – a little further down. But let me now give you a sneak peek overview graph about the benefits of time-restricted eating from a paper aptly called “Time-Restricted Eating to Prevent and Manage Chronic Metabolic Diseases” by a team of the world’s leading researchers from the Salk Institute:^​5​

• 

And the interesting part? These health benefits basically “exponentially increase” with every additional hour that you are not eating.^​2​ Especially if you move your eating window early in the day. So let’s have a look at that next.

Shorter Eating Window

Why You Should Make Time-Restricted Eating a Health Priority

You have seen that the first calories of the day tell your digestive organs to start all their digestive processes. Those digestive processes continue throughout the day until about two to three hours after you’ve consumed the last calories of your day. And only then can your digestive organs change to their repair and rejuvenation mode.

When you reduce the time that your organs need to spend on digestive processes, you increase the time they can spend to repair and rejuvenate themselves. And the smaller you keep your eating window, the more time your organs can spend to repair and rejuvenate themselves, and the more beneficial it is for your overall health. This is called time-restricted eating.

This means that the best time to eat is not a specific time, but a time-frame within which you should eat (read: consume all your daily calories). It is the differentiation between eating whenever you want (called ad libitum in literature) and restricting your eating timings to a specific eating window (called time-restricted eating).

Let’s get the introduction to time-restricted eating (more generally called time-restricted feeding in literature) from two of the greatest contemporary researchers on fasting and longevity, Valter Longo, and eating in the context of the circadian rhythm, Satchin Panda. Together, they wrote a paper titled “Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan” that states the following:^​4​

“TRF [time-restricted feeding] is a daily eating pattern in which all nutrient intake occurs within a few hours (usually ~12 hr) every day, with no overt attempt to alter nutrient quality or quantity. The concept of TRF arose within the context of circadian rhythms.”

Valter Longo and Satchin Panda

And how long exactly should your time-restricted eating window be? Frankly, as little as you can sustainably implement in your lifestyle.

You’ll already get great health benefits when you limit the time your organs have to work on your digestion to twelve hours (that’s an eating window of nine to ten hours plus two to three hours of digestion). And those health benefits then exponentially increase with every additional hour your organs get to repair and rejuvenate themselves.^​2​

“Start by establishing a 12-hour window for a week or two, and then try to decrease the time you eat by an hour a week. The reason to do this is that the optimum eating window is between 8 and 11 hours.

This is because the health benefits that you get from eating within a 12-hour window double at 11 hours, and double again at 10, and so on, until you reach an 8-hour window.

Eating for 8 hours or less may be feasible for some, or for many of us over a few days, but it becomes difficult for many people to sustain this over months or years.

While the science at 12 hours is impressive, lowering your window (to as few as 8 hours) is significantly advantageous.”

Satchin Panda

But does it matter when you start and finish your eating window? Or are some times more beneficial than others?

Earlier Eating Window

Why It Is Better To Have an Early Time-Restricted Eating Window Than a Late One

Research strongly suggests that there are differences whether you restrict your food intake to the earlier or later times of the day:^​6​

“Surprisingly, the results of TRF [time-restricted feeding] in humans appear to depend on the time of day of the eating window.”

Elizabeth Sutton et al.

Here’s the short summary:

• Early time-restricted eating (including eating during the middle of the day) has consistently shown great positive health outcomes.^​7,8​
• Late time-restricted eating (restricting food intake to the late afternoon and evening) has not consistently shown positive health outcomes, but mostly null results or even worsened some health markers.^​9–11​

And those differences are – you might have guessed it – because of your circadian rhythm.

I’ve mentioned beforehand that your circadian rhythm optimizes the timing of your body functions. And the daily rhythm of your digestive organs (from digestion to repair and rejuvenation) has been the dominant example so far. But there are more body functions involved in the process of making use of the calories you consumed.

Let me give you a few examples here of how your circadian rhythm shows:

• Melatonin is the hormone that signals your body to prepare for the night and its levels rise about 2 to 4 hours before your typical sleep time. Your metabolism slows down, your core temperature gets cooler, and all your other functions are getting ready for the night too. Any calories at that time interrupt all these processes and literally ignite your metabolism again. To make matters worse, food won’t move as fast through your digestive system anymore and some ends up sitting in your stomach during the night. That leads to a whole set of additional problems.^​2​
• The thermic effect of food is higher early in the day than later. This is your metabolic rate that your body increases after you ate. And it increases it more earlier in the day (which is something good) and less so later (which is not so good). Think about the thermic effect of food as the umbrella term for your metabolic processes to digest, absorb, and make use of the calories and nutrients you ate.^​12,13​
• Insulin sensitivity has a daily rhythm that is highest early in the day and gradually goes down. When insulin sensitivity is high, your cells need less insulin to store excess blood sugar (a good thing). But when insulin sensitivity is low, your cells need more insulin to store blood sugar (bad for your pancreas that then needs to produce more).^​14,15​ At the same time, the rise of melatonin interferes with your body’s ability to produce insulin.^​16​

In short, the circadian rhythm of your organs, your hormones, and every other body function that is involved in the digestion suggests that your metabolism is optimized for food intake early in the day.^​6​

Let me again put it in the words of Satchin Panda, the pioneer and leading researcher about time-restricted eating (a word he coined too):^​2​

“Eating late is by far the worst choice you can make”

Satchin Panda

What does that mean for you? Try to move your eating window as early as possible. Or better, try to stop eating as early as possible. Because those adverse health effects come from how your body reacts to food intake when it’s already preparing for the end of your day.

Evolutionary Origin

Why Is Time-Restricted Eating Vital For Our Paleoanthropological Bodies

Now, let’s put early time-restrictive eating in the context of our evolution. Why do we generally still crave food late in the evening when it would be healthier not to eat? And why wouldn’t our body make time for the repair and rejuvenation state of your organs independent of whether you just consumed calories or not? Instead of spending the next few hours digesting all your calories, even if those are just a few.

Speaking in evolutionary terms, because there has never been selective pressure for this. We simply never used to have access to food all day (and night) long. It was quite the opposite.

So let’s take one step back here and look through the lens of evolution: Why are calories so important and dictate the state of your organs? Because there was selective pressure during the largest part of our evolutionary history to make use of any and all calories that we consumed. Or, as Daniel Lieberman, paleoanthropologist at Harvard University, puts it in his monumental book “The Story of the Human Body: Evolution, Health, and Disease”:^​17​

“Getting dinner (or, for that matter, breakfast and lunch) probably does not dominate your list of daily concerns, yet most creatures are almost always hungry and preoccupied with the quest for calories and nutrients. To be sure, animals also need to find mates and avoid being eaten, but the struggle for existence is often a struggle for food, and until recently the vast majority of humans were no exception to this rule.”

Daniel Lieberman

That is why calories are still so important for our paleoanthropological bodies. And why they dictate the state of your organs and ignite your metabolism again when you consume them. Even if your circadian rhythm has already started to shut down your functions and prepare you for the night. And even though this means that your health is severely negatively impacted in the long term.

So, with that in mind, let’s have a look at some data about the average daily eating timings. Or, better, at how restricted (or not) they are.

Daily Routine

How Time-Restricted Eating Fits Into Your Daily Routine

With all that in mind, let’s have a look at your daily eating routine now. And let’s start with a simple question: What do you think, for how many hours do you eat every day?

If you are like most people, then you might believe that you eat within a 12-hour window. But then, most people do only count their “real” meals and forget to count any other calories they consume. Like their cream in their coffee in the morning. Or a glass of wine or any snacks after dinner. And when those are included as well, about half of the people eat for 15 hours or more. Which means that they eat basically all the time from waking up until going to bed.^​7​

But you are not like most people, so let’s count again:

1. Start counting with the first calories that you consume in the morning (and for your organs, any calories count – no matter if you consider it food or not).
2. Finish with the last calories you consume in the evening (again, all of them count).

Now, how long is your eating window?

Next step, figure out how many hours your organs are actually working on your digestion:

3. Take the length of your eating window and add 2 hours (or even 3 to be on the safe side).

So, how many hours do your organs spend digesting your calorie intake? And how many hours do you allow them every day to repair and rejuvenate themselves?

Do you want to get the final verdict from Satchin Panda, again? Sure, here you go:^​2​

“Look at the total number your stomach is at work: […] If this number is more than 12 hours, here’s the good news: You have something to work on and it will have one of the biggest impacts on your health for the rest of your life.”

Satchin Panda

But you’ve seen above that it’s not just the number of hours that your organs need to work on your digestion. It is also the timing of when you eat.

1. Have a look at when you consume your last calories (again, anything counts).
2. Compare this time with when you go to bed.

Is the difference at least three hours? Meaning that you allow your body at least three hours after you’ve consumed your last calories until going to bed?

Then (congratulations!) you’ve met the basics already. But, as you’ve also seen, the earlier you shift the time-restricted eating window when you consume your food – and hence the earlier you stop eating – the more beneficial it is for your health.

Here’s when you should eat – based on your circadian rhythm – if we put it all together:

• Go for a time-restricted eating window of ten hours or less every day.
• Try to finish your last bite or sip of calories as early as you can, but at least three hours before you go to bed.

Ok, but nobody is perfect, right? So what happens if you want to go out with friends on the weekend and eat or drink something together? Or if you want to have a “cheat day” for any other reason?

Cheat Days

How Bad Are Cheat Days or Cheat Weekends For Your Body When It Comes to Time-Restricted Eating

Let’s be clear on one thing: time-restricted eating is not a fad diet that comes and goes. It is a lifestyle that brings you closer to live in alignment with your body. To how your body has evolved over millions of years. And it is also a lifestyle that allows your body to follow your circadian rhythm.

But, as for anything, longevity aka consistency in the long-term is key. And that means that you should go for a time-restricted eating window that you can actually follow. One that helps you improve your quality of life. Instead of one that restricts you too much and makes you feel worse.

It’s better to stick to a routine that is less than perfect but that works for you than to abandon one that is perfect (at least in theory).

And if that means that you have a cheat day once in a while, don’t worry too much about it. Not because of what I say about cheat days, but because of what science says.

There are two tendencies (even though studies are still at a very early stage):

• In general, when you shift your eating times away from those that your body expects, then you interrupt the balance between digestion and repair and rejuvenation that your organs are used to. If you eat for longer (or also start earlier), this would mean that you interrupt their repair and rejuvenation phase and won’t allow them to finish their nightly processes.^​2​ But then, consistently allowing them enough time and then interrupting once is better than never allowing them enough time without interruption.
• One animal model study found that time-restricted feeding that was interrupted with unrestricted eating on the weekends, still significantly improved their metabolic health. And that was even though, in this study, mice were fed a variety of obesogenic diets that normally produce obesity and metabolic syndrome if fed ad libitum (unrestricted).^​18​

Now, what shall we make out of this? Try to stick to your (early) time-restricted eating window as consistently as possible. But don’t be too harsh on yourself if life gets in the way. And enjoy those cheat days instead. At least if they only occur once in a while. And then, the next day, continue with your normal (early) time-restricted eating window again.

Hormone Levels

Why You Should Give Your Hormones Time to Adapt to Your New Time-Restricted Eating Window

Now that we are talking about time-restricted eating, we also need to talk about you feeling hungry. Because that is what will happen. At least until you are used to your new eating window: When you restrict your eating window, you will initially still feel hungry at those times when you were used to eating. 

But have you ever wondered what it is that makes you feel hungry? And why you feel hungry at nearly the same time every single day?

Is it that you are starving and your body needs energy? Well, the average man has about 100,000 kcal (420,000 kJ) stored in body fat.^​19​ Given the daily recommendation of calorie intake, that’s about 40 days of eating stored.

So there’s still a lot to burn before your body runs low on energy. And then even more. This is one of the reasons why people can easily do a multi-day fast (for example, I am fairly lean and did a ten-day fast without any energy issues).

Plus, do you know that feeling of being hungry but then you are not able to eat. And later, when you finally have time to eat, you are not hungry anymore?

Here’s the solution to this riddle: your hormones.

There are two hormones in particular that control your hunger and satiety levels:^{​13,20,21​}

• Ghrelin is the hormone that makes you feel hungry.
• Leptin is the hormone that makes you feel full and satiated.

And those hormones have a circadian rhythm. At times when you normally eat, your body already prepares your organs to be ready to digest incoming food. 

• And the levels of ghrelin, the hormone that makes you hungry, go up in anticipation. But after a while, the ghrelin levels go down again. Even if you haven’t eaten yet. And, consequently, you don’t feel that hungry anymore. Also even if you haven’t eaten. 
• Leptin levels normally are high after eating a meal and give you that feeling of satiety. leptin levels reflect short-term cumulative energy balance. Leptin seems to maintain cumulative energy balance by modulating energy intake.

And here’s what happens if you eat all your calories in an early time-restricted eating window:^​13​

• Your ghrelin levels will go significantly down. This means that you’ll feel less hungry.
• Your leptin levels go slightly up. This means that you’ll feel slightly more full.
• And your circadian rhythm of these levels, in anticipation of your food intake, will adapt to your new eating times.

Now, what does that practically mean for you?

Simply be aware that your hormone levels need some time to adapt to your new (early) time-restricted eating window. And until they have adapted to your new eating times, you’ll need some willpower to overcome the feeling of being hungry. Even though this is just for a few days.

But, then, remember that you feel hungry because your body produces more of your hormone ghrelin, not because you are starving. And that you’ll be fine again when those ghrelin levels go down – even if you didn’t eat.

And once the circadian rhythm of your hormones ghrelin and leptin have adapted to your new eating times, there’s no more willpower needed. Your body will anticipate food at your new times and that’s when you’ll then feel hungry. Outside of your new (early) time-restricted eating window, you’ll even feel less hungry and more satiated. 

Want to know one tip that helped me overcome any food cravings early in the day? A pinch of sea salt under my tongue. Your body might just have run low on it overnight.

Health Benefits of TRE

Wat Are the Biggest Health Benefits of Time-Restricted Eating

Think about using your daily eating habits to improve your health. Conventional wisdom would tell you to either eat healthier (with many different interpretations of what this is) or to less. And up until as recent as 2012, that’s also where scientific studies were focused on.

Let me quote Satchin Panda from the famous Salk Institute, again, who changed the nutritional focus to another include dimension:^​2​

“All of nutrition science is based on two experiments. The first proved the notion of calorie restriction: If we eat less, we’ll lose weight and achieve better health. The second experiment supports the notion of a “healthy diet.”

Our experiment focused solely on the restriction of time for eating, and it produced amazing outcomes, establishing the idea that it’s not only how much we eat and what we eat, but when we eat that matters, especially for long-term positive health outcomes.”

Satchin Panda

With all you’ve learned in the first part of this article, it seems kinda strange that nutritional scientists didn’t pick up the timing component earlier, right? Especially since many health benefits of prolonged fasting were long-established until then.

So let’s have a look at this “third experiment of nutrition science” next. The one from 2012 when Satchin Panda showed the health benefits daily time-restricted eating. Based on your circadian rhythm.

You can get an overview of the most groundbreaking scientific discoveries from Satchin Panda’s lab at the Salk Institute here.

In 2012, Panda and colleagues asked the simple question of: “How much of disease is due to a poor diet, and how much is due to random eating?” 

And they then followed this up in an experiment with genetically identical mice. Where they controlled for pretty much every variable and only changed the eating window from unlimited feeding for the control group to time-restricted feeding for the study group.^​22​

	Unlimited food availability	Time-restricted feeding
Study subjects	Genetically identical mice…	…born to the same parents and raised in the same home.
What: Food quality	The same obesogenic diets (think about a standard American diet of both high-fat/high-sugar)…	…that are proven to produce obesity and metabolic syndrome in mice.
How much: Food quantity	The same daily amount…	…of total calories consumed.
When: Food timing	Unlimited: Ad libitum eating	Limited: 8-hour eating window
Results	Severe metabolic diseases, excess body weight, adverse blood sugar, and cholesterol levels.	Completely protected from any diseases, no excess body weight, normal blood sugar, and cholesterol levels.

In short, restricting the feeding window to only eight hours every day completely protected the study group of mice from any diseases or obesity. While the control group experienced all those negative health effects.

But here’s the thing: What do you think would happen when those now sick and obese mice, who used to have unlimited access to food, are put on a time-restricted feeding window? Again, with all other variables being the same.

The same study found that those adverse health effects could be reversed by putting the sick mice on a time-restricted feeding schedule. Take it from Satchin Panda again, who stated the following about this:

“More surprising, when we put sick mice on this scheduled feeding, we could reverse their disease without medication or change in diet.”

Now, when you think about all those chronic diseases that way too many of us will suffer at age (and that normally come to stay), doesn’t that sound at least a little promising? At least to me, it does.

Still, up to date, most of the studies are done with animals and still need to be replicated in human trials. The underlying model, however, is the same: When you restrict your eating timings, your body spends less time on your digestion and you allow your body more time to repair and rejuvenate itself. In a state called fasting (aka the time when you are not eating).

And here’s how two of the world’s leading researchers, Valter Longo and Satchin Panda, summarized the importance of those fasting periods for your health and longevity:^​4​

“Certain aspects of repair and rejuvenation that are integral to fasting-re-feeding physiology may be associated only with fasting. Hence, intermittent and periodic fasting may represent important factors in optimizing lifespan and healthspan. […]

Restricting the timing of food intake to a few hours without an overt attempt to reduce caloric intake, as in time-restricted feeding (TRF), may trigger the fasting physiology after a few hours of feeding cessation on a daily basis.”

Valter Longo and Satchin Panda

Now, I’m not sure how familiar you are with the art of scientific writing… But that’s pretty much as clear cut as it can get. So let’s jump into it.

Metabolic Health

How Time-Restricted Eating Can Improve Your Metabolic Health

When you think about your metabolic health, you can think about your body working well as a system. It is the state where your body can keep itself balanced.

And there are a few health markers that you could get checked to see if your body still has that balance. Among others, those are:^​7,23​

• Your systolic blood pressure.
• Your fasting glucose concentration.
• Your triglyceride levels.
• Your (visceral) body fat percentage.

You can view those as the basis to stay healthy. But if they are too much out of balance, then your body simply cannot function properly anymore. This is called the metabolic syndrome. 

Below are the most common metabolic diseases that occur when your metabolic health is out of balance (metabolic syndrome):

• Cardiovascular diseases (especially heart attack and stroke), which are the leading cause of death worldwide^​24,25​
• Cancers, which are the second leading cause of death worldwide^​26,27​
• Diabetes and high blood glucose, which are another leading cause of death worldwide^​28,29​
• And various other systemic diseases^​30​

One big problem is that those are chronic diseases. And the most common treatments for those metabolic diseases treat the underlying health markers. But those are still just the symptoms of a deeper problem. And going after those identified enzymes, receptors, or other targets often lacks efficacy but comes with a wide range of side effects.^​4​

Here’s what Valter Longo and Satchin Panda stated in their paper titled “Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan” about this approach:

“Although processes by which the drug target and drug are identified are highly sophisticated, resulting intervention can be viewed as rather unsophisticated strategies.”

Valter Longo and Satchin Panda

What would be a more sophisticated strategy? To allow the body to “trigger sophisticated physiological responses resulting from billions of years of evolution.”^​4​

And this is where time-restricted eating comes into play. Especially through allowing your body enough time to repair and rejuvenate itself during the time when you are not eating – during your fasting period.

It is already well established in animal models that time-restricted feeding can prevent and even reverse those studied animals from developing metabolic syndrome. And that they are also protected from it when they are fed an obesogenic diet that is proven to otherwise provoke metabolic diseases.^{​18,22,31​}

Human trials in this field of time-restricted eating are novel, but they have already shown similarly promising results. Let’s have a look at one meta-analysis paper that systematically reviewed the current literature about “Beneficial Effects of Time-Restricted Eating on Metabolic Diseases.”^​23​

Here’s what they’ve found about the impact that time-restricted eating can have on some of the most important markers for your metabolic health:

Time-Restricted Eating	Metabolic Health Markers
Significantly lowered	systolic blood pressure
Significantly lowered	fasting glucose concentration
Significantly lowered	triglyceride levels
Significantly decreased	(visceral) body fat percentage

In short, time-restricted eating significantly improves vital markers for your metabolic health.

What does that mean for you on a deeper level? Time-restrictive eating has shown promising results to improve many of your organ functions by simply increasing the time when you are not eating. Because certain aspects of the repair and rejuvenation process of your organs only occur during this fasting time.^​4​

Your body and organs might just thank you through improved liver function, adipose tissue function, heart health, gut health, and brain health. The result? You might be able to prevent metabolic syndrome or manage chronic metabolic diseases.^​5,32​

Are you also interested in the positive health impact that your circadian rhythm can have on your immune system? You can read all about it here in: “How to Use Your Circadian Rhythm to Boost Your Immune System”

So far, the majority of time-restricted eating studies on humans have centered around weight loss. But the results of other mammal studies (that still need to be replicated with us humans) are promising. So far, time-restricted eating has shown efficacy against:^{​1,33,34​}

• Cardiovascular diseases
• Some types of cancer
• Diabetes and blood glucose levels
• And even neurological disorders

Speaking about improved health and reduced risk for diseases… At the same time that time-restricted eating allows your organs to repair and rejuvenate themselves, it also allows each and every one of your cells to repair and recycle themselves. In a process called autophagy.

Autophagy

How Time-Restricted Eating Can Boost Autophagy In Your Cells

Your cells have a mechanism to detect and then repair or recycle damaged or dysfunctional parts, such as their proteins, membranes, or organelles. And this mechanism is called autophagy.^​1​

The word autophagy originates from the Greek words “auto” (which means “self”) and “phagein” (which means “to eat”). It describes that your cells basically “eat themselves” in this process. 

And before diving into the connection to time-restricted eating, I want to highlight its importance by sharing with you that the 2016 Nobel Prize in Physiology or Medicine was awarded to Yoshinori Ohsumi for his discoveries of mechanisms for autophagy. To be more precise, he received it for his discoveries that “elucidated mechanisms underlying autophagy, a fundamental process for degrading and recycling cellular components.”^​35​

But why am I telling you this? Because there is a strong connection between fasting and autophagy. Let’s take it again from Valter Longo and Satchin Panda:^​4​

“One of the consequences of […] fasting is the activation of autophagy, which is known to play an important role in aging and lifespan.”

Valter Longo and Satchin Panda

Here’s how it works within your cells.

When you constantly eat, then your cells receive a relatively steady supply of nutrients. And while this sounds great, it isn’t. Because this means that your cells are in a constant growth-mode where autophagy is suppressed. That means that cell division is prioritized over cell repair.^​36​

So, not eating – fasting – is important to activate autophagy. And the more you restrict your eating window, the more time you allow your body to fast.

And while it already sounds great to allow your cells to repair and recycle themselves, instead of duplicating damaged or dysfunctional parts, there’s more to it.

Humaira Jamshed and colleagues summarized it best in their paper aptly titled: “Early Time-Restricted Feeding […] Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans”^​37​

“Autophagy has been shown to play a major role in protecting against multiple chronic diseases such as diabetes, heart disease, cancer, and neurodegenerative diseases, by recycling damaged and used proteins and organelles. Increasing autophagy may have anti-aging or rejuvenating effects.”

Humaira Jamshed et al.

A common feature of many major chronic diseases is the accumulation of protein aggregates within and outside of cells. And through autophagy, your cells can remove those.^​1​

At least if you let your cells repair and recycle themselves. Through the frequency and circadian timing of your meals. And, as we’ve seen above, that would ideally mean for you through early time-restricted eating.

Weight Management

How Time-Restricted Eating Will Help You With Weight Management

When you think about weight management from your body’s perspective, it is simply about getting rid of excess body fat. Especially that in the wrong places.

The worst of these places is in between your organs, where it prevents them from working properly. This is also known as visceral fat. And it affects a great many people, including those that we colloquially call “skinny-fat.”

And when you restrict your daily eating window, you allow your body to take care of those excess fat storages. Until your body finds its balance again. That’s why:

• Your body particularly breaks down your visceral fat (the one in between your organs).^​34,38​
• Your body is also able to stabilize its weight and get rid of excess body fat even if you don’t restrict your calorie intake.^​22,39​

Your body composition is an important factor for your metabolic health. So much so that when Shinje Moon and colleagues did a systematic review (called a meta-analysis) of studies about the benefits of time-restricted eating, they found a clear difference between metabolically healthy and unhealthy participants:^​23​

“In the metabolic unhealthy participants, TRE showed a significant reduction in body weight. In the healthy participants, TRE did not show weight reduction, but still showed beneficial effects such as fat mass reduction. This means TRE has beneficial effects on participants with or without metabolic dysfunction.”

Shinje Moon et al.

In short, your body weight might go hand in hand with your metabolic health. And if you restrict your eating window, you allow your body to improve both of these.

Let’s get more specific now and have a look at one concrete study.

One of the first studies that tracked the eating behavior of participants found out that the majority eats for fifteen hours or more every single day. Basically from the time they wake up until the go to bet.^​7​

In this study, a subgroup of overweight individuals then changed to a self-selected 10-11 hour eating window. Without any further instructions. The results after 16 weeks?

• They naturally and unknowingly reduced their daily caloric intake (some of this came from a reduction in late-night alcohol and snacks).
• They lost a significant amount of body weight and kept this for up to a year.
• They also reported improved sleep at night and elevated alertness during the day.

Now back to you. If you want to lose bodyweight – either to improve your body composition or your metabolic health – how should you best go along?

• Have your time-restricted eating window as early as possible: Studies found that your weight loss will be greater if you consume your calories earlier rather than later.^​5​
• Extend your fasting time for as long as possible: Most of your body’s fat-burning happens 6 to 8 hours after finishing your last meal and increases almost exponentially after a full 12 hours of fasting. This makes any amount of time fasting past 12 hours highly beneficial for your weight loss.^​2​

And the beauty about the efficacy of time-restricted eating is that you can achieve all of this without altering the quantity or quality of what you eat. 

And while I personally have never worried about the quantity of what I eat (I let myself be guided by listening to my body), I’m highly concerned about both the quality and timing of my food intake.

Glucose, Insulin, and Diabetes

How Time-Restricted Eating Can Stabilize Your Glucose and Insulin Levels and Help With Diabetes

Speaking about the quality of what you eat. It is well established that food high in glycaemic index (think about carbohydrates in general and especially in processed or sugary foods) that are quickly broken down by your body provokes an insulin response in your body. 

Here’s how it works on a basic level:^​40,41​

• The higher the glycemic index of your food is, the faster its carbohydrates will be digested and enter your blood as glucose (blood sugar).
• Your body always keeps a very tight level of blood glucose and the higher the amount of glucose that enters your blood (blood sugar spike), the more immediate the reaction of your body to normalize your blood sugar levels again.
• Your body primarily does this through the insulin pathway: Insulin triggers the uptake of glucose into your liver, your adipose tissue (your fat cells), and also into your muscles.
• Both your liver and your muscles have limited storage capacity for glucose. And everything in excess of that will have to be stored in your adipose tissue (your fat cells).

So far so good about the basic process of what happens when you eat foods that increase the glucose concentration in your blood (your blood sugar levels). 

There are two more important factors in this process:^​42​

• Insulin is produced in your pancreas, by your pancreatic beta cells.
• Insulin sensitivity determines the amount of insulin your cells need to absorb and store glucose from your blood. The lower your insulin sensitivity is, the more insulin your pancreas has to produce.

Let me give you some background information on how this translates to one of the biggest metabolic diseases, diabetes:

“Type 1 diabetes occurs predominantly in young people (diagnosis at 30 years of age or younger) and is generally thought to be precipitated by an immune-associated destruction of insulin-producing pancreatic beta cells, leading to insulin deficiency and an absolute need for exogenous insulin replacement. Type 2 diabetes is a progressive metabolic disease that is characterized by insulin resistance and eventual functional failure of pancreatic beta cells.”

Aidin Rawshani et al.

And here’s what that means for your pancreas and insulin production: When your blood glucose levels constantly get elevated through eating (especially high glycemic food), also your pancreas has to constantly produce insulin so that your glucose is taken up by especially your adipose tissue (fat cells). 

Over time, however, your cells’ insulin sensitivity goes down. That means that your pancreas needs to produce more and more insulin to stabilize your blood sugar levels. Until a point of failure where it simply cannot produce enough insulin anymore and your blood sugar level stays elevated. At this point, you’d officially have developed type 2 diabetes.

And here comes knowledge about both your circadian rhythm and time-restricted eating into play. Because they can both help you to never reach this point.

The first part: The connection between your circadian rhythm and both blood glucose and insulin:

• Blood glucose increase after a meal is lowest in the morning and highest in the evening.^​43​
• Insulin sensitivity peaks in the morning and steadily goes down during the day until it reaches a low at night.^​14,15​
• Melatonin release in the evening inhibits insulin production (limits the amount of insulin produced by your pancreas).^​16​

Practically speaking, what does that mean for you? It means that your body is basically not made to handle blood sugar spikes later in the day. On the one hand, your cells are less insulin sensitive meaning that they need more insulin to store any given amount of glucose. And on the other hand, your pancreas is inhibited in its insulin production. So, you’d need more insulin, but your body’s upper limit is less.

This is one of the reasons why early time-restricted eating is so beneficial for your health.

But if you, for whatever reason, still want to eat later in the day, try to only eat food with a low glycemic index. In this way, your blood sugar levels won’t spike as much. So that your pancreas doesn’t have to produce as much insulin either.

So, if you have to eat carbs in the evening: Exercise also has another function that is especially helpful for you in the evening: It helps your muscles to take up glucose (the sugar in your blood that comes from any food or drinks with carbohydrates) in a way that is not dependent on insulin.^​32,44​

The second part: The connection between time-restricted eating and both blood glucose and insulin:

• Time-restricted eating leads to a significant reduction in glycemic response to a meal (this particular study showed a 36% reduction)^​45​
• Early time-restricted eating is correlated with lower 24-hour blood glucose^​37​
• Early time-restricted eating leads to lower fasting and overall insulin levels.^​6​
• Early time-restricted eating significantly improves insulin sensitivity.^​6​
• With time-restricted eating, your pancreas doesn’t have to constantly produce insulin. And it has more time to repair and rejuvenate itself and don’t let itself.^​2​

What does this mean for you?

With (early) time-restricted eating, you can help your body to improve your insulin sensitivity again. Meaning that your pancreas won’t have to produce as much anymore. And you also give your pancreas more time to rest. Which additionally reduces the strain on its workload.

Let’s connect these points to diabetes again: While time-restricted eating can’t help you much with type 1 diabetes, it is more than promising as a lifestyle intervention for type 2 diabetes.^{​6,45–47​}

Myths About TRE

What Are the Most Common Myths About Time-Restricted Eating

Now, with all the benefits you’ve just seen that come from (early) time-restricted eating, you might wonder why there are still so many myths out?

Or at least, I’ve wondered that. And here are the three most common reasons I can come up with why time-restricted eating has still a long way to become the norm again:

1. It is against our human intuition: Many people simply might not be able to grasp why or how it could be beneficial to not constantly eat. And to feel hungry in the transition period.
2. Cultural stories promote the opposite: Since the advent of agriculture about two-hundred generations ago, we more or less started regularly eating three meals a day. And this is also the eating pattern that is still rooted in our cultures. But this eating pattern also neglects the millions of years of evolution that we went through to reach this point.
3. You can’t sell it as a product: Much of food advertising goes into selling the need to constantly eat. From all the claims for healthy breakfast to dinner to snack and drinks. Many objectively unhealthy foods and drinks also get labels that would suggest otherwise. It is simply in the financial interest of those companies to convince you to buy and eat & drink more (aka all the time).

Let me restate our incoming quote from Mark Mattson, from both the Department of Neuroscience at John Hopkins University and the Laboratory of Neurosciences at the National Institute on Ageing, and colleagues again to highlight those points from an evolutionary perspective. In their paper titled “Meal frequency and timing in health and disease,” they stated the following:^​1​

“The most common eating pattern in modern societies, three meals plus snacks every day, is abnormal from an evolutionary perspective.”

Mark Mattson et al.

So, let’s dive into some of the most common myths around time-restricted eating.

Continuous Calorie Need

Myth: You Constantly Need Calories and It Is Not Safe to Go For Too Long Without Eating

One of the most common myths is that your body needs constant energy in the form of calories. And that not eating for too long is dangerous for you.

This myth might come from the miserable feelings of what happens when your glycogen stores run low. This is one problem of our modern, carbohydrate-heavy diets. Our bodies are simply not used to burning fat as the primary energy source anymore. 

An average man has about 100,000 calories in body fat stored but only about 2,000 calories in glycogen stores. And when the latter runs out, we tend to feel it quite strongly. Even though there’s more than enough still stored in our body. But what do most people do? Eat anything carb-heavy (aka with a high glycaemic index) to continue this cycle. Instead of allowing their body to tap into their own body fat storages.^​19​

Now, I’ve told you beforehand that I did a ten-day water & tea fast without any problems even as a fairly lean person. But what do you think, for how much longer could we fast?

Eventually, that depends on the amount of body fat. But no matter what you’ve guessed, I’m pretty confident that your number didn’t even come close.

Let’s have a quick look at the Scottish patient Angus Barbieri, who, one day turned to a local hospital doctor to fast under supervision. His weight at the beginning was 456 lb (207 kg). So he had a lot of energy reserves stored. And knowing that he’d eventually run low on nutrients, he got regular doses of multivitamins, yeast, and sodium among others.^​48​

So, how long did his fast last? More than one year. 382 days in total to be precise.

And why did he stop? Not because of health issues. But because he reached his goal weight of 180 pounds (82 kg).

• 

Now, most of us don’t have that many calories stored to feed on for that long. And fasting above a few days also gets you in trouble with some nutrients if you don’t replenish them.

But the overall message stays the same: There’s absolutely no need to constantly eat. If there were, we would not have survived in our evolutionary past when we regularly went for stretches without food.

Quite the contrary: We evolved with stretches of fasting. And our bodies adapted accordingly, which might be the reason why it is vital for our health that we allow our bodies to tap into fasting periods.

Slower Metabolism

Myth: Your Metabolism Slows Down When You Don’t Constantly Eat

Another big myth is that your metabolism slows down when you restrict your eating window. 

Let me cite one recent study here that had a look into this topic, with the telling title: “Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans”^​13​

Study participants were split into two groups. One on an early time-restricted eating window and a control group. After four days they changed and their energy expenditure and metabolic measures were assessed. 

The result? You might have guessed it from the title, but their energy expenditure didn’t change. Consequently, also their metabolism didn’t slow down.

Increased Appetite

Myth: You Are Constantly Hungry When You Limit Your Eating Window

Now, the myth that you are more hungry when you restrict your eating timing couldn’t be further from the truth. Because it’s the exact opposite that happens. Time and time again, studies found that time-restricted eating reduces appetite.^​6,13​

Do you remember that your feelings of hunger and satiety are basically controlled by two hormones:

• Ghrelin is the hormone that makes you feel hungry.
• Leptin is the hormone that makes you feel full and satiated.

Let’s have a look at the above study again, where participants were split in either a time-restricted eating group or a control group. And then, after four days, switched their eating patterns for another four days.^​13​

Here’s how their hormone levels changed when they were in the early time-restricted eating group:

• Their ghrelin levels significantly went down.
• Their leptin levels went slightly up.

And how did they subjectively feel? Just as you’d have expected from those measurements: Their hunger levels were diminished and they felt fuller. And all that compared to eating on the control schedule, where they could eat pretty much all day long.

Weight Loss Only

Myth: Time-Restricted Eating Is Only About Weight Loss

The most studied benefits of time-restricted eating are centered around weight loss. So far so true. But that’s only one health marker. And that’s only because research focus and money went into that direction.

But early time-restricted eating also improves many other health markers, independent of weight loss.

That is exactly what Elizabeth Sutton and colleagues established in 2018 when they conducted the first supervised controlled feeding trial to test whether the health benefits of early-time restricted eating are independent of weight loss. To do so, they ensured that the participants were fed “enough food to maintain their weight.”^​6​

The result? Many of the health benefits of early time-restricted eating are indeed independent of weight loss. The title of their research paper summarizes their findings quite nicely: “Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss”

Muscle Loss

Myth: You Lose Muscle Mass When Restricting Your Eating Window

Ok, now to the final myth around muscle mass. One big concern is that you’d lose muscle if you restrict your eating timings. 

Now, let’s have a look at this from the perspective of your body first. What’s the most important thing to maintain your muscle mass? Well, you might have guessed it already, your muscles need a sufficient amount of protein and especially amino acids (the building blocks of proteins).^​49​

Luckily, and quite contrary to conventional wisdom and much money spent on advertising, there’s no special window directly after training where you have to eat your protein.^​50​

And now to the effects of time-restricted eating on your muscle mass. Here I’d like to share two studies with you:

The first study had a look at a group of resistance-trained men that were split up into one group that ate all their calories within eight hours and one control group. Both groups then went on with the same resistance training. The result with respect to their muscle mass? Both groups maintained their muscle mass. But it was the time-restricted eating group that lost significantly more body fat.^​8​

The second study had a look at resistance-trained women that were split up into one group with an eight-hour eating window and one with a thirteen-hour eating window per day. Did those females lose muscle mass? Nope, quite the contrary. Rather they gained muscle mass (at a similar level to the control group).^​51​

In short, you won’t lose muscle mass because of time-restricted eating. If anything, then you’ll rather gain muscle mass. And lose body fat. To me, that sounds like the perfect combination to build lean muscle mass (and it’s actually what I’m doing too).

Personal Experiences

My Personal Experiences

I have been doing (early) time-restricted eating for a few years now. And while it initially took some time to get fully used to it, a few things have helped me on the way. And I wanna share those with you here.

How did I start? Initially, I did start with the popular 16/8 eating window where I started eating at noon and finished at eight pm. And my experience was that I somewhat always felt the desire to eat in the morning and was always looking forward to breaking my fast.

What helped me then was especially to take on plenty of fluids:

• I have been drinking a big glass of water first thing in the morning.
• And I have been drinking one big pot of green tea before lunch.

I feel like taking on enough fluids has helped me overcome any intense feelings of appetite. Which leaves me wondering: Maybe I had mistaken being thirsty for being hungry?

One other thing I’m big about is my salt balance. If I’m getting appetite (mostly still without being hungry), I can often overcome it by putting a pinch of salt under my tongue. In that case: Maybe my body did just tell me that it was running log on salt?

Either way, if I’m going for a longer run, swim, or bike before my first meal, I always take a bit of salt. And in a strange way, that feels to me as if I’m eating my pre-exercise nutrition.

What am I doing now? For quite some time, I’ve switched to a short eating window of just a few hours around lunchtime. 

I initially got started with that change after doing a ten-day water fast as kind of my new New-Years-Resolution tradition (aka the best way to achieve the most important health resolution for the year already in the very first days).

And what were the biggest changes that I felt there?

• My sleep improved massively. I needed about 90 fewer minutes of sleep every night and my sleep quality improved at the same time (which wasn’t bad to start with). I just woke up so full of energy that there was no way for me not wanting to continue this.
• After a few days of fasting, I learned to view hunger as simply a feeling of my body that it expects food. A feeling that I can accept or manipulate.
• I was happy about all the additional time I gained from not preparing and eating.

Based on this experience, I switched to an early time-restricted eating window of about three to four hours every day. 

• My sleep quality is still awesome most nights (even though not quite as high as during the fast).
• My body is fully used to my new eating times and now expects food only during a small window.
• I’m happy about the additional time gained from just preparing one meal a day (plus eating a lot of snacks like dark chocolate, macadamia nuts, or coconut yogurt with chia seeds, berries, and cacao nibs).

Now, it feels important for me to say that I do have a few exceptions too. Because I don’t want to restrict my social life because of an eating pattern that is not connected to society standards. No matter how connected that is to how my body evolved to eat.

Those exceptions are few and far in between, but probably every other week or so I might join in for a later dinner. With no bad feeling whatsoever. And then simply continue as usual the next day.

And my final tip for you is to not limit yourself too much:

• If there’s a special event once in a while, don’t feel bad to break out of your (early) time-restricted eating window. That used to happen in our evolutionary history too. And, as we’ve seen above, it doesn’t have too many adverse effects.
• The most important part is that you are consistent over time. And even a small change will have massive compounding effects in the future. If you stay consistent most of the time.

View (early) time-restricted eating as a lifestyle that you are happy to follow.

Key Takeaways

Key Takeaways

Finally, there are three key takeaways that I want to share with you about the best time to eat based on your circadian rhythm – time-restricted eating:

1. When you eat aligned with your circadian then you limit your eating window during the day to allow your organs to repair and rejuvenate themselves instead of constantly working on your digestion. This is called time-restricted eating.
   • The first calories signal the start of the day for your organs. And your organs have to switch from repair and rejuvenation to digestion.
   • And the absence of calories signals the end of their day. And your organs finish their digestive processes about two to three hours after you consumed your last calories and can only then start their repair and rejuvenation again.
2. Early time-restricted eating is the healthiest and the smaller you keep your eating window, the more time your organs can spend to repair and rejuvenate themselves, and the more beneficial it is for your overall health. This is called time-restricted eating. 
   • Keep your eating window as short as possible.
   • Finish eating as early as possible.
   • Your hormones (that signal hunger and satiety) will need some time to adapt to your new eating timings. So it is normal to initially feel hungry outside your new eating window. But this lasts only for a few days
   • Consistency over time is key. Try to stick to your new early time-restricted eating window as consistent as possible. But don’t let that get into the way of your life. A cheat day once in a while doesn’t throw you off too much. Just continue as normal the next day.
3. Early time-restricted eating has many health benefits for your whole body.
   • First human studies show promising results to prevent or even reverse metabolic disease.
   • Fasting activates autophagy, the vital process where cells repair and recycle themselves. And autophagy has been shown to play a major role in protecting against multiple chronic diseases.
   • When you restrict your daily eating window, you allow your body to take care of your excess fat storages. Especially the visceral fat that affects a great many people, including the “skinny-fat” ones.

And now back to you: Do you already know for how many hours you let your organs work on your digestion every day? And for how many hours you allow your organs to repair and rejuvenate themselves? And, consequently, for how many hours you allow your body to tap into its natural healing mechanisms?

Stay fit,

PS: If you found this information useful, spread the word and help those who would benefit most from it 🙂

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