Fasting & Time Restricted Eating

What is Time-Restricted Feeding?

Time-restricted feeding is a way to control one’s eating habits by limiting the eating window to a particular phase of each 24-hour day. 

It involves fasting and eating, which establish different biological conditions in the body. Huberman will also explain how different methods of time-restricted feeding, such as eating every other day or alternating between eating for five days and fasting for two days, can lead to different outcomes.

Benefits of Time-Restricted Feeding

Mental Focus & Clarity

One of the biggest advantages of TRF is that it takes the decision-making out of the equation. When you follow a TRF schedule, you don’t have to think about when you’re going to eat or what you’re going to eat, because you already know when your eating window begins and ends. 

This can help you avoid the constant negotiation with food that many people experience when they try to restrict portions.

In addition to being a more straightforward approach to eating, TRF can also have a positive impact on your mental focus. 

When you don’t have to think about food all the time, you’re free to focus on other things, like work, exercise, or spending time with your family and friends. 

This clarity of mind is one of the reasons that many people have been drawn to TRF and find it to be a successful and sustainable way to manage their weight and improve their overall health.

It’s important to note that the food choices you make during your feeding window are also going to be very important. 

Some foods will increase your blood glucose levels and leave you feeling hungrier and more prone to overeating, while others will help regulate your blood glucose levels and allow you to be more in control of your food choices. 

Enhancing Weight Loss from Body Fat: Hepatic Lipase

According to a review, following a time-restricted feeding schedule for a minimum of 60 days leads to metabolic changes in the way people metabolize energy. 

This shift towards burning more fat, relative to other tissues, is driven by an increase in the enzyme hepatic lipase, which metabolizes fat for lipolysis and energy production. 

Time-restricted feeding also reduces CIDEC, a lipid droplet associated lipolysis inhibitor, allowing the system to use a higher percentage of fat when in a caloric deficit.

The best way to ensure that the weight you lose is mostly from body fat stores is by following a sub-caloric diet along with time-restricted feeding. 

A sub-caloric diet means that you are consuming fewer calories than you are burning, which is a foundational element for weight loss. A 10-hour or 8-hour feeding window maintained for several months will allow the system to shift towards burning more fat and using it for energy production.

Time Restricted Feeding Protocol: Rules

According to the research, there are two key pillars of intermittent fasting that should be considered as part of your protocol. 

The first is to not eat any food in the first hour after waking and potentially for longer. This allows your body to get into a fasted state, which is essential for promoting weight loss, metabolic health, and liver health.

The second key pillar is to not eat or drink anything for two to three hours before bedtime. This allows your body to continue to fast as you sleep, which can help regulate blood sugar levels and promote better health outcomes.

Of course, there are nuances to these rules, such as whether or not coffee and tea can break a fast. But by adhering to these two key principles, you’ll be on your way to maximizing your health and weight goals with intermittent fasting.

When to Start & Stop Eating

During sleep, our bodies undergo a number of different processes to recover and repair cells and tissues. This includes autophagy, which is a process that cleans up dead or sick cells. 

Fasting of any kind can enhance autophagy, but it’s important to note that it’s not the only way to create autophagic conditions.

So when is the best time to eat? 

According to recent research, the answer lies in extending the sleep-related fast either into the morning or starting it in the evening. This means that you’re already fasting when you’re asleep, and the depth of that fast depends on how long it was since your last meal. 

If you fast early in the day and you’ve been asleep for six to eight hours, you’ll already be in a fasted state. 

To take advantage of this, it’s recommended to not eat for at least the first 60 minutes after waking, and to extend the fasting until 9 a.m., 10 a.m., 11 a.m., or even later in the day.

This information is backed by a recent review published in the journal Endocrinology Reviews, titled “Time-Restricted Eating for the Prevention and Management of Metabolic Diseases.” 

This paper, written by Satchin Panda’s lab, is a comprehensive review of over 100 studies on time-restricted feeding in humans, with detailed references and descriptions of outcomes.

How to Shift Your Eating Window

One of the key pieces of advice that Dr. Huberman offers is to allow yourself a transition period when moving to a time-restricted feeding schedule. 

This period can last anywhere from one week to ten days, during which you should shift your feeding window by about an hour each day. 

Once you establish a feeding window that feels comfortable and that you think you can maintain, it’s important to stick to that schedule for at least 30 days, if not indefinitely.

One of the interesting findings from Dr. Huberman’s research is that people often think they’re eating within an eight-hour window, but in reality, their feeding window is much broader. 

Even those who are strict about their feeding schedule can experience drift, particularly on weekends, where their feeding window may shift around. This drift can cause disruptions in the circadian clock mechanisms, which can offset the positive health effects of intermittent fasting.

Dr. Huberman emphasizes the importance of being consistent with your feeding window and placing it in a portion of the 24-hour cycle that you can stick to most days. 

He acknowledges that it can be challenging to maintain a consistent feeding window, especially given that we have access to food 24/7. However, he suggests there are things we can do to help offset the drift, such as taking certain measures or adopting specific strategies.

Different Feeding Windows Types

Eight Hour Feeding Window

The data suggests that the eight-hour feeding window is the most beneficial across all parameters, including inflammation, weight loss, and fat loss. Furthermore, people tend to have better adherence to this feeding schedule, making it easier to stick to in the long-term.

Four to Six Hour Feeding Window:

Interestingly, the four to six hour feeding window seems to produce the opposite effect, as people tend to overeat during this period. This results in no change in body weight or even an increase in body weight.

One Meal Per Day:

While there have been very few studies on the one meal per day schedule, the results have been mixed. Some people maintain or lose weight on this schedule, while others may be under eating, which could have negative consequences for their health.

Eating Every-Other-Day 

Another popular feeding pattern is alternate-day fasting, where people eat one day and then fast or eat very few calories the next day. 

This pattern has been found to result in significant weight loss and reduced resting blood glucose levels in obese individuals. 

Although it can produce more rapid effects than time-restricted feeding, it may not be feasible for everyone to maintain for a long period of time. However, it has been given a “safe bill of health” as it has not been shown to cause bone loss or any major detrimental effects.

While there is a community online exploring the benefits of longer fasts for the sake of offsetting or reversing dementia, there is currently no quality clinical, peer-reviewed study to support these claims. It is also worth noting that the long-term effects of every other day fasting, such as rebound weight gain and blood glucose levels, have not yet been thoroughly studied.

Effects of Specific Categories of Food

Food volume is an important factor to consider. It’s common knowledge that large meals take longer to digest than small meals, so it’s important to learn how to gauge food volume to determine what works best for your body.

Food type is another factor that affects gastric emptying time. Foods high in fat will slow gastric emptying, meaning it takes longer for your body to transition to a fasted state. 

On the other hand, consuming calories in liquid form will result in faster gastric emptying. Additionally, foods that lead to a big and steep rise in glucose, such as pure sugars, will result in a drop in glucose levels. When combined with fats, glucose levels rise more gradually and are more sustained.

It’s important to establish a feeding window that you can manage on a regular basis. Whether it’s a 6-hour, 8-hour or 10-hour feeding window, make sure it fits into your social and life context.

What Breaks a Fast? Rules & Context

To arrive at a scientific answer to whether or not something breaks a fast, one would need to wear a continuous glucose monitor and measure blood glucose levels after ingesting different foods or drinks. 

Blood glucose levels are the most significant readout for determining whether your body is in a fed or fasted state. However, for most people, wearing a continuous glucose monitor is not practical, and there are simple rules that can be followed.

Drinking water, tea, and black coffee will not break your fast, nor will ingesting caffeine in pill form. However, foods that contain simple sugars, such as a can of soda or a slice of pizza, will break a fast. 

Artificial Sweeteners, Plant-Based Sweeteners

Artificial sweeteners and fasting have been a topic of debate for a long time. While some believe that consuming artificial sweeteners like aspartame and sucralose while fasting can lead to an increase in hunger and a decrease in blood glucose, others believe that these sweeteners do not interfere with fasting. However, the data on this subject is mixed, and there are not enough good studies exploring the impact of these sweeteners on fasting.

The best way to determine whether or not artificial sweeteners break a fast would be to wear a continuous glucose monitor and test the impact of these sweeteners on blood glucose.

However, this is a difficult study to carry out, given the individual variation in terms of discipline, appetite, and other factors.

In general, the plant-based non-sugar sweeteners like Stevia seem to have a minimal impact on overall blood glucose when consumed in moderation. However, there is evidence that consuming artificial sweeteners in excess can have detrimental effects on the gut microbiome.

Glucose Clearing II, Cinnamon, Acidity, Salt

Lemon and lime juice, surprisingly, can lower blood glucose levels by virtue of the fact that it will reduce blood glucose due to its acidity. Cinnamon is also a mild glucose disposal agent and can reduce blood glucose levels.

Salt, in particular, plays a vital role in maintaining mental and physical health during fasting. Neurons use electrolytes such as sodium, potassium, and magnesium to perform their functions of chemical and electrical signaling. 

Taking a pinch of salt, ideally Himalayan or sea salt, can stabilize blood volume and offset feelings of lightheadedness and shakiness.

It is important to note that people with chronic hypertension or high blood pressure should be wary of ingesting too much sodium. However, for most people, ingesting salt in moderate amounts can be beneficial and provide immediate relief from feelings of hunger and jitters during fasting.

Toothpaste, Wine, and More

In addition to that, there are some frequently asked questions about fasting that may seem odd, but are still important to address. For example, people often ask if brushing your teeth with toothpaste will break your fast. 

The answer is no, unless you’re swallowing the toothpaste. If you want to be extra sure, you could try using a continuous glucose monitor while brushing your teeth.

Another common question is whether a half glass of wine after dinner will break your fast. The answer is yes. Wine contains one gram of sugar and has been shown to disrupt the fasting state based on the “one gram of sugar effect.” It’s important to keep in mind that these are sensitive metabolic processes, even after a meal.

Accelerating the Path to Fasting: Light Movement, High-Intensity Training, and Glucose Clearing

One concept that can help us transition from a fed to fasted state more quickly is glucose clearing. You may have heard the old adage that taking a 20-30 minute walk after dinner helps you digest food more quickly. This is indeed true, as light movement and exercise can increase gastric emptying time and speed up the transition to a fasted state.

For those who can’t get outside, indoor light exercise such as air squats and pushups can help clear glucose, but for most people, simply taking a light walk is sufficient. 

If you’re looking to accelerate the transition to a fasted state even further, consider engaging in high-intensity interval training (HIT). 

A recent study found that the effects of HIT on blood glucose can vary depending on when it is performed. If performed in the afternoon or evening, HIT can lower blood glucose levels and help you enter sleep in a more fasted state. On the other hand, HIT performed early in the day can increase blood glucose levels, which is often associated with the shuttling of nutrients to the muscles that have just done a lot of work.

Protein Consumption & Timing for Muscle

A recent study, published in July 2021 in the peer-reviewed journal Cell Reports, has shed light on the distribution of protein intake in different meals delivered either early in the day or later in the day. 

This study, performed in both mice and humans, focused on hypertrophy training and found that muscle tissue is better able to undergo hypertrophy when protein is ingested early in the day.

The study also looked at the effects of supplementing branched chain amino acids (BCAAs), which are popular in strength training and bodybuilding circles. 

The results showed that ingesting protein early in the day supports muscle tissue maintenance and growth by regulating the expression of the BMAL protein synthesis pathway within muscle cells.

However, it is important to note that the study does not suggest that ingesting protein later in the day is bad for you. Instead, it emphasizes the positive effects of ingesting protein early in the day for muscle maintenance and hypertrophy. 

This is especially relevant for individuals who are mainly concerned with muscle maintenance and hypertrophy, as well as for those who practice time-restricted feeding and are interested in deriving the health benefits of this mode of eating.

For those who practice intermittent fasting, the ideal feeding window of eight hours should be shifted to the later part of the day to allow for the ingestion of protein early in the day. However, there are various other ways to organize meals and eating patterns, such as small meals spread throughout the day or larger meals earlier in the day.

The Impact Sunlight and Food on Our Circadian Rhythm

Light is the primary way in which the genes and the clock systems of our body get organized, or entrained, meaning matched to the outside light-dark cycle. 

Viewing light early in the day and in the afternoon is ideal, ideally that sunlight, and avoiding light in the middle of the night is also great. The second most powerful timekeeper is food and when you eat, and the results of the study underscore this point.

If you want to be healthy, it is important to view light at the appropriate times of each 24-hour schedule and to eat at the appropriate time of each 24-hour day. 

Eating during the nocturnal phase of the 24-hour cycle is very detrimental to one’s health and can cause negative health effects. 

One way to ensure that your organ health and metabolic health are entrained properly is to engage in time-restricted feeding, with a window of feeding that falls during your more active phase.

Adherence Matters: Choosing the Right Diet Plan for You

One of the major issues with any diet study is adherence. In a study, people are often incentivized or compensated in some way to follow the diet plan. However, in the real world, people don’t have a researcher monitoring them, and most people don’t consistently log all their food. This is why it’s important to consider your own lifestyle when choosing a diet plan.

Portion control can be a challenge for many people too. Some find it easier to not eat for certain periods of each 24-hour cycle, while others find it manageable to eat smaller portions throughout the day. 

For some, like Huberman, portion control can be a struggle. Eating only half a croissant is not a satisfying option, and eating the entire croissant creates a rise in blood glucose and hormones associated with highly palatable food.

The Ideal Fasting Protocol 

Based on the research of Dr. Satchin, a leading expert in the field, it is recommended to avoid ingesting food for at least 60 minutes after waking up and to avoid all food (even one gram of sugar) for two to three hours prior to bedtime. 

It is ideal to sleep for eight hours and extend the fasting period around sleep to maximize health benefits.

An eight-hour feeding window is the best target for most people, as shorter feeding windows (4-6 hours) can lead to overeating and potential weight gain. 

One meal per day type eating may have advantages, but there is limited research on this approach and it may not be feasible for most people.

When choosing a feeding window, it is important to be consistent and place it at the same time every 24 hours to avoid “jet-lagging” the system. 

The optimal placement of the feeding window would be in the middle of the day (10 a.m. to 6 p.m.), but this may not be practical for everyone.

Incorporating light exposure, especially early morning and all-day bright light, can help offset any potential negative effects of shifting the feeding window. Avoiding bright light in the middle of the night is also important for maintaining good mood and metabolic function.


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