Fasting And Sleep: The Restorative Connection

Key takeaways

• Sleep does count as fasting and as part of your fasting window. 

• Getting an adequate amount of good quality sleep can directly benefit your fasting results.

• When you sleep, your body is performing vital repair tasks that support metabolism, cellular repair, brain function, energy supply, and hormone regulation.

• Many fasting benefits are closely aligned to those of restorative sleep, including cellular cleanup and improved glucose management.

• Practicing circadian fasting, or time-restricted eating (TRE) not only times your eating patterns to your own biological clock, but may also enhance metabolism and hormone production for improved sleep results.

If you’re exploring or practicing intermittent fasting or other fasting protocols, you may find yourself very attuned to how many hours you’re clocking between meals. But what about the hours spent in bed—does sleeping count as fasting? In this article, we’ll explain why sleep is inherently a fasting period and explore the ways in which prioritizing quality sleep can enhance the benefits you may achieve from fasting. Whether you’re new to fasting or a seasoned pro, taking steps to optimize restorative sleep can be a useful tool for maximizing your fasting window, while also improving overall health. 

Does sleep count as fasting?

Yes! The hours you’re asleep do count as fasting; in fact, sleeping is your body’s most natural form of fasting. While you sleep, your body isn't taking in food or water, prompting it to shift into a repair mode, supporting metabolism, regulating hormones, and cleaning up damaged cells in a way similar to fasting. For this reason, if you’re practicing any form of fasting—from intermittent fasting to prolonged fasting protocols such as the 5-Day Fasting Mimicking Diet (FMD)—sleeping certainly counts as part of the fasting window.

What happens in your body while you sleep?

Human beings spend (or should spend) nearly one-third of their lifetime sleeping. It's no wonder, then, that those precious hours at the end of each day are responsible for a whole host of vital biological maintenance projects. Here are some of the ways your body is still working hard to preserve your health and longevity, even while you’re sleeping: 

• Metabolism: During sleep, your body continues to burn calories (approximately 50 calories per hour). In fact, metabolism only decreases by about 10% during sleep, because processes like fat oxidation continue, allowing the body to shift from using glucose (energy from carbohydrates) to burning ketone (energy from fat) for fuel. Since you’re not consuming any calories while you sleep, your body can also focus less on digestion, and more on improving other aspects of your health. 

• Cellular repair and recovery: Being less physically active while you sleep makes it easier for your body to heal injuries and repair any cellular and tissue damage that may have occurred during your waking hours. (This is also why you tend to feel more tired when you’re sick!)

• Brain function maintenance: The brain actually stays quite active during sleep, and getting an adequate amount of quality sleep each night helps us form and maintain the brain pathways responsible for learning new things and creating memories. It also allows the brain to clear out information it doesn’t need, remove any toxins that may have accumulated during the daytime, and aid in our ability to concentrate and respond quickly during waking hours. 

• Energy resupply: When you’re awake, your cells use stockpiled resources to perform their necessary functions, but while you sleep, they get the opportunity to resupply and restock ATP (adenosine triphosphate), their primary molecular energy source. This replenishment helps fuel your activities for the next day.

• Hormone regulation: Sleep influences the regulation and metabolism of several hormones like melatonin, cortisol, leptin, and ghrelin which are responsible for things like growth, stress management, energy levels, and appetite control. Hormones related to glucose and lipid metabolism are also affected by the body’s circadian rhythm (the biological changes that occur throughout each 24-hour cycle).

With so much happening inside your body during sleep, it’s no surprise that getting too little—or poor-quality—sleep doesn’t just leave you feeling tired. It can also disrupt key biological processes that help protect against serious health conditions like heart disease, cognitive decline, diabetes, obesity, and depression.

What happens in your body when you fast?

Much like sleep, fasting also affords your body an opportunity to perform some maintenance and cellular cleanup without the distraction of digestion. In the first 12-24 hours of fasting, your body will utilize glucose (blood sugar) as its primary source of energy. After several hours without food, however, the glucose stores become depleted, and your body shifts into ketosis, the process where it breaks down fat for fuel instead. 

This metabolic flexibility that allows your body to switch fuel sources then helps mitigate significant risk factors for disease like chronic inflammation, obesity, and insulin resistance. After around 72 hours of fasting (prolonged fasting), autophagy, the biological mechanism responsible for clearing out or recycling old and damaged cells to prioritize healthier ones, kicks in. Via the autophagy process, cells are then able to function better and behave more youthfully, which means the organs and tissues they comprise also perform better, resulting in the potential for enhanced longevity overall. 

Time-restricted eating (TRE) can help support circadian rhythms

A circadian eating pattern involves consuming all your meals within a 12-hour window (particularly from sunup to sundown) followed by a 12-hour overnight fast. This approach aligns your eating habits with your body’s natural rhythms. Because circadian rhythms regulate key functions like sleep-wake cycles, metabolism, and hormone production, syncing your meals with them can help support better digestion, energy levels, and overall health.

One of the ways to potentially get even more benefit from a circadian eating practice is to follow The Longevity Diet principles. Taken from the habits of populations living in regions with the highest number of centenarians, these principles include eating a mostly plant-based diet with some fish, in addition to prioritizing whole grains, fresh vegetables, and mono- and polyunsaturated fats like nuts and seeds. 

How fasting and sleep work together

Now that we know some of the crossover characteristics of restorative sleep and fasting, let’s find out how they can work together to benefit your health and longevity.

• Hormone regulation: Fasting may help regulate insulin and growth hormone levels, both which play a role in metabolism and fat burning; getting good sleep can help keep these hormones balanced to ensure they function optimally, which only enhances the benefits of fasting.
  
  

• Glucose management: Research suggests that fasting might have a stabilizing effect on blood sugar levels over time, which supports healthy metabolic markers and the reduction of insulin resistance. Consistent sleep is essential in this process, as poor sleep may lead to blood sugar spikes or dips, undermining fasting efforts.
  
  

• Metabolism: Fasting encourages the body to burn fat for fuel, a process known as ketosis. During deep sleep, your body works to process fat and recover from daily wear and tear, which may help improve fat-burning efficiency.
  
  

• Circadian rhythm support: Studies show that fasting aligns well with your circadian rhythm, which is linked to improvements in digestion, metabolism, and hormone secretion. The more in tune we are with this intricate biological clock, the better our chances of achieving consistent, high quality sleep as well.

Improving your sleep hygiene to enhance your fasting benefits

Despite the clinically-proven health benefits that can come from combining mindful fasting practices with a regular sleep regimen, studies show that one in three adults still do not get enough sleep. Here are some helpful tips for improving your sleep hygiene, which may then also serve to enhance your fasting results too: 

• Stay hydrated: Drinking enough water throughout your day is vital for preventing dehydration-related sleep disturbances. Adequate hydration is also crucial for fasting success, since dehydration can lead to electrolyte imbalances, among other side effects. However, try not to drink too much water right before bed so you can avoid the need to get up in the middle of the night to use the bathroom. 
  
  

• Schedule your eating window strategically: If you’re intermittent fasting, aim to align your eating window to a 12:12 circadian eating pattern, which follows The Longevity Diet principles, and ensures your body won’t be digesting food when it should be focused on resting. By giving your body enough time to digest before sleep, you allow for deeper rest, and more efficient cellular repair from fasting too.
   

• Limit caffeine intake: Caffeine is a known disruptor of sleep, and it’s recommended to limit your intake during fasting especially. If you do choose to include caffeine, it’s generally best to limit it to your morning hours to avoid sleep issues.
  
  

• Exercise: Even mellow physical movement like taking a walk for 20-30 minutes a day can help support better glucose control and help you feel more tired and ready for bed when the time comes. However, during prolonged fasting periods, it’s advisable to practice gentle exercises only.
  
  

• Maximize your sleep routine: Relax before bed with a warm bath, easy reading, or some soft music. Curate your room for sleep by limiting bright lights and loud noise, keeping the temperature cool but comfortable, and avoiding TV or any other screen use in the bedroom. With time, these steps help signal the body’s circadian rhythm that it’s time to wind down for rest.
  
  

• Be consistent: Make an effort to create a regular sleep schedule, and be mindful about adhering to it as best you can. Consistency helps the body better adapt to new habits and can improve the long-term results of both fasting and sleep patterns. 

The better you sleep, the easier you fast

Sleep is a natural extension of your fasting window, but it can also be a valuable contributor to fasting success when its quality is prioritized every day. In a fast-paced world where we often disregard our body’s most basic needs in the name of meeting deadlines or packing too much into our waking hours, consistent and restorative sleep is one of the first things many of us sacrifice. Whether you’re considering a fast or just hoping to improve your overall health with some simple steps today, making sleep a wellness priority is a powerful and effective place to begin.

For more information about The Prolon 5-Day Fasting Mimicking Diet (FMD), reach out to our team and we’ll be happy to answer any personalized questions you may have.

Sources: 

American Heart Association. “What happens when we sleep, and why we need just the right amount each night.” Website. 

Cleveland Clinic. “Autophagy.” Website.

Cleveland Clinic. “Sleep.” Website.

National Heart Lung And Blood Institute. “How Much Sleep Is Enough?” Website. 

National Institute of General Medical Sciences. “Circadian Rhythms.” Website.

National Institute of Neurological Disorders And Stroke. “Brain Basics: Understanding Sleep.” Website. 

National Library Of Medicine. National Center For Biotechnology Information. “Cerebral metabolic changes during sleep.” Website. 

National Library Of Medicine. National Center For Biotechnology Information. “Effect of Intermittent Fasting Diet on Glucose and Lipid Metabolism and Insulin Resistance in Patients with Impaired Glucose and Lipid Metabolism: A Systematic Review and Meta-Analysis.” Website. 

National Library Of Medicine. National Center For Biotechnology Information. “Fasting, circadian rhythms, and time restricted feeding in healthy lifespan.” Website. 

National Library Of Medicine. National Center For Biotechnology Information. “Physiology, Fasting.” Website. 

National Library Of Medicine. National Center For Biotechnology Information. “Physiology of Sleep.” Website. 

National Library Of Medicine. National Center For Biotechnology Information. “The Impact of Sleep and Circadian Disturbance on Hormones and Metabolism.” Website. 

NPJ. Metabolic Health And Disease. “Insulin resistance reduction, intermittent fasting, and human growth hormone: secondary analysis of a randomized trial.” Website. 

Science Direct. “Metabolic Flexibility and Its Impact on Health Outcomes.” Website.