Fasting and Sleep: Here’s What You Should Know

Expert Verified ByExpert Verified By: Peter Nastasi, NASM Certified Sports Nutrition Coach and Kristen Casey, PsyD
fasting and sleep

Fasting has garnered widespread attention for its potential role in weight management and improving metabolic health.There’s a good chance you know someone who has committed to a fasting regimen at some point, or perhaps you’ve even tried it yourself. Interestingly enough, fasting has found itself back in the spotlight, only this time it’s sparked interest in the realm of sleep science. 

Some researchers suggest that the timing and nature of our eating habits play a pivotal role in the quality of our rest. In this article, we’re uncovering what you need to know about fasting and sleep, including how your eating schedule can impact your rest and other ways to support a healthy sleep routine.

Long Story Short

  • Fasting is the practice of alternating between windows of eating and windows of abstaining from food. While it’s become popular more recently, fasting has been practiced for centuries.
  • Potential benefits of fasting include weight management, better blood sugar control, heart and brain health, longevity, and improved sleep.
  • Conclusive evidence on fasting and sleep is limited. It’s best to incorporate other lifestyle habits to help improve your sleep routine and restfulness.

What Is Fasting?

While fasting has captured the attention of many health enthusiasts, it’s not a new concept. The practice of fasting has roots in cultural and religious traditions, more recently sparking the curiosity of scientists. While it’s been traditionally associated with spiritual rituals, its potential physiological benefits are also being explored. (1)

At its core, fasting involves voluntarily abstaining from food and, in some cases, beverages (besides water) for a specified time. Many people determine a set period in which they can eat and a set period of fasting (often, mostly overnight while asleep) that remains the same over each 24-hour window. For example, this might look like a 10-hour eating window from 7 a.m.  – 5 p.m. and a 14-hour fasting window from 5 p.m – 7 a.m. 

Others choose to adhere to more extended periods of fasting all at once, such as a full 24-hour fast 1-2 days per week. Some people opt for one day of very low-calorie intake (approximately 500 calories) every few days, with normal eating days in between. While options vary, it’s always best to consult with your healthcare provider to ensure whatever fasting style you pick is healthy. 

How Fasting Affects Sleep

With all the talk about how fasting may benefit health, you might be curious whether following a fasting practice could support your sleep. 

According to sleep scientist Dr. Carleara Weiss, “Intermittent fasting with limited food intake in the evening and nighttime may strengthen circadian rhythm and improve sleep quality and duration. This type of fasting may be beneficial for people with hectic sleep patterns.” 

Some evidence suggests that fasting has an impact on your circadian rhythm — AKA your body’s internal clock that tells you when to go to sleep and when to wake up. (2) Additionally, older research indicates that occasional, short-term fasting may improve sleep by reducing how often you’re woken up by things like leg movements. (3) 

Still, research is mixed. Some studies have found that fasting can reduce rapid eye movement (REM) sleep, which could have negative effects. (4) And a 2021 review found that while fasting supported weight loss, there wasn’t enough data to say it benefitted sleep. (5) 

Some researchers think fasting may change your gut microbiome — the community of bacteria that live in your digestive tract and influence overall health — in a way that supports better sleep. (6) Fasting could also promote weight loss that improves sleep for some people, notes Weiss. 

Additionally, fasting may affect your hormones. For instance, it could boost the production of ketone bodies, which are molecules made by your liver as it breaks down fats from your diet. Ketone bodies act like an alternative energy source to glucose (sugar), particularly for your brain, during times of very low carbohydrate intake (or fasting). Some research suggests that an increase in ketone bodies may influence brain chemicals and hormones involved in sleep regulation, but this isn’t well understood yet. (7) (8)

Overall, Dr. Weiss notes that the evidence on fasting is evolving, so we need to take it with a grain of salt. Fasting can have different impacts on different people. How it affects sleep can also be influenced by other lifestyle factors. 

The Importance of Consistency 

The research on fasting and sleep is mixed. (9) Weiss notes, “The caveat is the population under investigation, for example, age, gender, body weight and BMI, and chronic diseases such as diabetes [may vary].” Simply put: What works for one type of person may not work for another, and there isn’t enough conclusive evidence to draw conclusions about fasting and sleep just yet. 

Once you settle on a comfortable fasting and eating schedule, stick to it — and be sure your schedule is realistic for you. Starting too aggressively, such as with a long fasting period during awake hours, can be unsustainable. And if you find you’ve jumped in a bit too ambitiously and need to make changes, that’s okay! If it’s not working for you, feel free to make adjustments. 

Overall, finding a consistent approach that works for you is key. Weiss recommends a circadian-conscious approach for mealtime and sleep, understanding whether you’re a morning person or an evening person, and following a regular daily schedule for food, exercise, and sleep. 

How Much Sleep Do You Need When Fasting? 

The amount of sleep you need — fasting or not — depends on your individual needs. While there’s no one-size-fits-all answer, maintaining a consistent sleep schedule is important even during fasting periods. Not getting enough sleep can do more than just make you cranky and foggy the next day. It may even affect your metabolic health, interfering with any benefits you may see from fasting. (10) 

Overall, experts recommend a minimum of seven hours of quality sleep per night for adults, fasting or not. (11) In general, there shouldn’t be any reason for your sleep needs to significantly change when you’re fasting. What matters most is striking the right balance for your lifestyle. 

Other Potential Benefits of Fasting

Beyond fasting and sleep, this practice has garnered attention for several other potential benefits. While more research among humans is needed, some of these benefits may include: 

  • Healthy weight management (12)
  • Better blood sugar regulation (13)
  • Improved heart health (14)
  • Improved brain function (15)
  • Enhanced longevity (16)

When Fasting Isn’t For You

Nonetheless, fasting isn’t for everyone. It’s not uncommon to experience side effects like nausea, headache, fatigue, and digestive upset. Some people even report more difficulty sleeping when fasting. (17)

Certain groups of people should exercise caution or avoid fasting altogether, such as: 

  • Children and adolescents: Growing bodies have unique nutritional requirements, and fasting may impact their growth and development. (12)
  • Individuals with eating disorders: Fasting can potentially exacerbate unhelpful eating behaviors and may not be appropriate for those recovering from or at risk of eating disorders. (18)
  • Individuals with a history of metabolic disorders: Conditions like hypoglycemia (low blood sugar) may be aggravated by fasting. (19)
  • Athletes: Individuals who are training multiple hours per day, especially those looking to optimize athletic performance should likely avoid fasting. These individuals need a constant supply of calories to support their daily activity levels and ensure proper recovery. (20)

Furthermore, Weiss says, “Pregnant and breastfeeding people and those with chronic conditions such as cardiovascular diseases should not try fasting.” Fasting during these periods may deprive the body of essential nutrients needed for fetal development and lactation. Fasting could also impact medication management for people with existing health conditions. (12) (21) 

“Additionally, fasting is primarily aimed at weight loss and improving metabolism. Some studies focused on intermittent fasting to enhance the metabolism of people with diabetes and high cholesterol,” says Weiss. 

She continues, “There are other modalities of fasting, such as calorie-restricted fasting, where food consumption is restricted on a 10-hour window during the day, that is aimed to improve metabolism in overweight and obese persons. I would not recommend fasting if none of these conditions apply to you.” 

Overall, Weiss recommends anyone considering fasting for better metabolic function should seek specialized healthcare guidance rather than a DIY diet. Meeting with a registered dietitian knowledgeable in fasting may be helpful. 

Tips For Sleeping Better While Fasting

Sleep is important regardless of whether you practice fasting. Here are a few tips to help improve your restfulness routine.

Practice Good Sleep Hygiene 

One of the best things you can do to improve your rest is to practice good sleep hygiene habits. Sleep hygiene refers to a set of behavioral, environmental, and lifestyle practices that promote good, quality sleep, like: (22)

  • Creating a sleep-promoting environment in your bedroom
  • Only use your bed for sleep and sex
  • Going to bed and waking up around the same time each day
  • Establish a relaxing bedtime routine to prepare you for sleep

Stay Hydrated 

Your adult body is around 60 percent water at any given time, and normal fluid losses (like sweating and going to the restroom) need to be replenished through proper hydration practices. (23) Staying hydrated also helps support your sleep because it: (24) (25)

  • Helps regulate your body temperature so you’re not too hot or too cold during the night
  • Prevents dehydration, which can have uncomfortable symptoms like dry mouth and nose
  • Helps improve stress and anxiety, making it easier to fall asleep
  • Supports hormonal balance, like melatonin, which is important for the sleep cycle
  • May help prevent night wakings that result from being thirsty

Just avoid gulping down a ton of water right before bed, as the numerous trips to the bathroom during the night aren’t exactly conducive to improved restfulness.

Avoid Blue Light

Blue light is a modern problem that surrounds us the majority of the time. Emitted from technology — including laptops, cellphones, televisions, tablets, and more — blue light has been shown to disrupt the sleep-wake cycle by interfering with melatonin production. (26)

Normally, melatonin is released at the end of the day in preparation for sleep and its levels are reduced in the morning to help wake up your brain. However, blue light exposure later in the day has been shown to delay melatonin production, making it harder to fall asleep. (27) That’s why many experts recommend using blue light-blocking glasses and avoiding technology use close to bedtime. (28)

Practice Meditation

Meditation can be a valuable tool for promoting relaxation and reducing stress and anxiety. Engaging in mindful meditation techniques, such as deep breathing, progressive muscle relaxation, or guided imagery, may release tension and calm the mind. 

By redirecting focus away from racing thoughts and worries, meditation helps create a mental environment conducive to falling asleep. Regular meditation practice has been associated with improvements in sleep duration and quality. (29) Of course, meditation doesn’t come easily to everyone — it be tricky at first, but if you keep at it, you may experience some great potential benefits.

FAQs

Does fasting still count when you’re sleeping?

Fasting is the practice of abstaining from food, so it doesn’t matter what you’re doing as long as you’re not eating. You can still benefit from fasting even if the majority of your fasting period is while you’re asleep. In fact, many people find overnight fasting to be easier, as it prevents them from being hungry for an extended period.

How do I stop feeling tired when fasting?

It’s not uncommon to feel tired during fasting, especially as your body adjusts to changes in eating patterns and available fuel. If you notice you’re feeling excessive tiredness while fasting, you might consider adjusting your fasting period under the supervision of your healthcare provider. Other habits like staying hydrated, prioritizing nutrition during your eating periods, monitoring your caffeine intake, and getting enough sleep and exercise can help support normal energy levels.

The Last Word From Sleepopolis 

While it may offer benefits in certain situations, the larger verdict on fasting is still out. Limited evidence suggests that fasting may help align your circadian rhythm and potentially improve your overall sleep. Still, most of us are more likely to benefit from being intentional about our sleep hygiene habits. If you’re having trouble sleeping, consider where you could make lifestyle adjustments and speak with your healthcare provider for tailored advice.

Sources

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          Weiss, C. Personal interview. January 12, 2024.

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