Intermittent Fasting and Sleep

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Written by Afy Okoye

Reviewed by Dr. Michael Breus

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Some research suggests intermittent fasting may help people sleep better. Since intermittent fasting is currently a popular method for weight management, those interested in it might be curious about how this way of eating could affect their sleep. 

People practice intermittent fasting in different ways. The time of day a person fasts, the amount of weight they lose from fasting, and how much water they drink during their fast may all play roles in the way intermittent fasting affects sleep.

What is Intermittent Fasting?

Intermittent fasting is a way of eating in which people only consume food during certain times of the day or certain days of the week. Many people fast for health reasons or to lose weight, but fasting is also a part of some religious traditions. Some fasting regimens allow water, but certain religious fasts do not allow any drinking. 

How Does Intermittent Fasting Work?

Intermittent fasting appears to primarily affect the body by changing a person’s metabolism at a cellular level. For example, when people aren’t fasting, they usually get the energy they use from sugars in the blood. During fasting, the body must turn to other sources of energy stored in the liver and fat tissues.

Intermittent fasting that restricts eating to certain daytime hours may help align a person’s circadian rhythms with their environment. Circadian rhythms are physical changes that take place in a 24-hour cycle, including the sleep-wake schedule, body temperature fluctuations, and metabolism. Misaligned circadian rhythms may contribute to obesity and other health issues.

Science of Fasting and Sleep

Some studies have found that people sleep better while intermittent fasting, but this isn’t a certainty. Other studies have found that intermittent fasting doesn’t affect sleep quality. These varying results may stem from differences in how much weight research participants lost or the times of day they chose to eat and fast.

Some experts believe that the weight loss resulting from intermittent fasting could improve sleep. A type of intermittent fasting that aligns eating times with a person’s circadian rhythm may also improve sleep.

You ever notice that you get hungry at particular times in the day? That’s your circadian rhythm. Not only does it regulate our sleep patterns, but our daytime patterns as well.
Dr. Michael Breus

Other researchers suggest that eating only between the hours of 8 a.m. and 6 p.m. is best, given the normal fluctuations of a person’s daily circadian rhythms. The body’s circadian rhythms affect the health of cells, organs, and tissues, and help manage the release of hormones. 

Circadian rhythms regulate the release of hormones that regulate sleep and wake times, body temperature, appetite, and digestion at certain times of the day. These hormones include cortisol, which prepares the body for activity, and ghrelin, which promotes appetite. Mainly eating in the morning and afternoon may help to optimize the levels of these hormones. 

Conversely, fasting during daytime hours and eating at night has been shown to reduce levels of melatonin, a hormone that promotes sleep. This suggests that fasting during the day could potentially disrupt sleep rather than improve it.

Fasting and Insomnia

Few studies have examined how intermittent fasting may impact people with insomnia, and those that have found no effect. However, some researchers suspect that fasting for 2 to 5 hours before sleeping could reduce insomnia symptoms by reducing acid reflux. But fully understanding how fasting affects insomnia will require more research.

Some researchers point out that fasting could make insomnia worse if people become dehydrated while they fast. Since people normally get a portion of their daily fluids through food, fasting could increase dehydration symptoms if they don’t drink extra to make up for lost fluids. Limited evidence suggests that insomnia can be one symptom of dehydration.

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Health Benefits of Fasting

While the evidence to date is somewhat limited, researchers have proposed several health benefits that could be related to intermittent fasting.

  • Weight loss: Although intermittent fasting has not been shown to be more effective than other weight loss diets, some studies have found people lose weight while following it. Some people find they are not overly hungry while practicing intermittent fasting, which can help people follow the diet better than others.
  • Disease prevention: When intermittent fasting results in the consumption of fewer calories, it could help prevent cells from changing in unhealthy ways. These may include keeping certain genes from turning on in ways that could trigger the start of disease. 
  • Reduced cholesterol: Fasting every other day may reduce LDL or “bad” cholesterol and triglyceride levels in people with obesity. However, it could be that weight loss, rather than intermittent fasting itself, affects these levels.
  • Brain health: Intermittent fasting may reduce a person’s risk of having a stroke or developing Alzheimer’s disease. Additionally, animal studies suggest that intermittent fasting can slow the development of neurological disorders like Parkinson’s disease, but more research will be needed to determine whether this is true in humans.

Risks of Fasting

The most common risks of intermittent fasting include dehydration, low blood sugar, dizziness, and weakness. Dehydration becomes more likely during fasting, since the body usually obtains some of the fluid it needs from food. For this reason, people should consider drinking extra fluids while fasting. 

Intermittent fasting isn’t recommended for those who may be more vulnerable to the possible side effects of irregular eating, including:

  • Pregnant or breastfeeding people
  • Children and teenagers
  • Adults over 75 years old
  • People with a low body mass index (BMI)

Additionally, some common medical conditions are incompatible with fasting. 

  • Eating disorders: Among some people with eating disorders, fasting could trigger disordered eating or make the disorder worse. 
  • Diabetes: Although some research suggests intermittent fasting can benefit people with diabetes, it may also be dangerous. Fasting may reduce blood sugar too much, especially when a person is on diabetic medications. People with diabetes should consult with their doctors before engaging in any fasting. 
  • Active infection: People with active infections of any kind should avoid fasting. When fighting off an infection, the body needs extra energy, which requires both adequate nutrition and hydration. 

What Are the Types of Intermittent Fasting?

People practice intermittent fasting in various ways. Some of the most common methods depend on the number of meals a person eats or the amount of time they go without food.

  • Time-restricted eating: People who practice this type of intermittent fasting limit their eating to certain hours each day. For example, a person might eat over the course of eight hours, then fast for 16 hours, or eat over 12 hours, then fast for the next 12 hours. Some researchers suggest optimal eating hours are between 8 a.m. and 6 p.m.
  • B2 fasting: In B2 fasting, a person practices a specific type of time-restricted eating that involves two large meals each day. Often, a B2 regimen involves eating breakfast and lunch, but no dinner. Breakfast eating might be confined to the hours of 6 and 10 a.m., and lunch eating confined to 12 and 4 p.m.
  • One meal a day (OMAD): As the name suggests, OMAD is a type of time-restricted eating that consists of eating only one meal per day. Usually, this meal is eaten at a consistent time each day, such as between 5 and 7 p.m.
  • Alternate day fasting: In complete alternate day fasting, a person abstains from eating for a 24-hour period every other day. Another type of alternate day fasting involves eating only 20% to 25% of the regular amount of food every other day. 
  • Other types of 24-hour fasting: Some people practice intermittent fasting by not eating for 24 hours once a week, which may be called weekly fasting. Others fast for two 24-hour days each week, then do not fast on the other five days. This is often called 5:2 fasting, and may include days of low-calorie eating.
  • Religious fasting: Some people fast as a part of their religious beliefs. Many Muslims fast during Ramadan, and other religions such as Christianity, Buddhism, Judaism, and Hinduism have fasting traditions as well. During Ramadan, people fast from dawn to sunset, then eat between sunset and prior to dawn.

How to Sleep Well When Fasting

While practicing intermittent fasting, it’s important to sleep well to get the most benefit from your fast. Not getting enough sleep is linked to health concerns such as obesity and poor control of blood sugar levels. Certain habits can help people maintain energy levels, get the nutrients they need during fasting, and also promote good sleep. 

Drink Enough Fluids

Dehydration makes it harder to sleep well, and fasting can make dehydration more likely. The average person normally gets about 20% of their daily fluids from food. For this reason, people should consider drinking extra fluids while they are fasting.

Limit Caffeine

Caffeine can boost your mental and physical energy, but too much caffeine or having it too late in the day can interrupt your sleep. If you use caffeine, consider limiting it to no more than 200 mg daily, which is about three cups of coffee. If you’re prone to sleep disruptions, avoid caffeine within six hours of bedtime.

Choose Healthy Foods

Experts stress the importance of eating a balanced diet during non-fasting times. For instance, consider eating healthy foods from the Mediterranean diet—such as whole grains, legumes, nuts, vegetables, fruits, lean meat, and fish—between fasting periods. This diet may help improve sleep by reducing inflammation or improving metabolism.

Maintain Consistent Sleep and Eating Schedules

When possible, keeping a consistent sleep schedule can support your circadian rhythms and improve your sleep. Similarly, eating at consistent hours each day, especially in the morning and early afternoon, can help keep your circadian rhythms aligned with the daily cycle of light and darkness.

Improve Your Sleep Environment

Try these strategies to keep your bedroom dark, quiet, relaxing, and cool, which may improve your sleep: 

  • Hang blackout curtains to block out external light
  • Wear earplugs to block out sounds
  • Usie a white noise machine to drown out background noise
  • Remove distractions like TVs from your bedroom
  • Keep work and other unrelaxing activities out of your bedroom 

About The Author

Afy Okoye

Staff Writer, Sleep Health


Afy is a writer and creative strategist in San Francisco with a master’s degree in international health policy from the London School of Economics. She has written for VeryWell Health, BlackDoctor.org, and Paste magazine and edited peer-reviewed journal manuscripts for Elsevier. Afy says her work with The Sleep Doctor is anything but “sleepy.” She enjoys the opportunity to learn new information and share knowledge that gives people the power to make better choices. Afy also likes to read non-fiction, do creative writing, and travel solo.

  • POSITION: Side sleeper
  • TEMPERATURE: Hot Sleeper
  • CHRONOTYPE: Bear

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