Snooze University

Why Intermittent Fasting Can Cause Insomnia

by Dale Cudmore | Updated: Jun 02, 2023

In the long run, most people find that intermittent fasting helps them sleep better, if anything.

However, it’s quite common for people to report that fasting causes sleep issues in the short term.

It typically takes about 1-3 weeks to go away. If you’d like to learn why, and potential treatment methods, keep reading.

Important: If your sleep troubles don’t improve over a short time period, or you have any other physical symptoms, go see a medical professional as soon as possible. Diet changes can sometimes come with uncommon dangerous side effects.

Reasons Why Fasting Causes Insomnia

While not all of these likely pertain to your particular situation, there are 8 main ways that fasting can cause sleep trouble that may develop into a type of insomnia.

Fasting Often Increases Energy and Adrenaline Levels

The most likely reason for fasting sleep difficulties is because it has a significant effect on energy metabolism.

There are 3 main ways that it does so:

  1. Increases growth hormone - Growth hormone is vital for good health as it stimulates cell growth (in muscle, bone, etc.), which in turn makes you feel good and energetic (1).
  2. Fasting increases metabolic rate - Short term fasting leads to your body burning more calories. In a study of a 4 day fast, energy expenditure went up by 14% (2).
  3. Fasting affects insulin levels - Fasting helps your body learn to regulate levels of hormones like insulin. This is good long term, but until your body adjusts, irregular levels of insulin can lead to more orexin production, which gives you more energy and also inhibits sleep (3).

The common sense theory for this is that if you’re fasting, you need to have energy to go search for food. But more energy makes it harder to sleep.

SummaryIn the short term, fasting can lead to higher energy levels that makes it harder to sleep. Most people adapt to it in a few weeks, but it may also require exercising more or changing sleep duration.

Adapting to Burning Fat Can Alter Circadian Rhythm

Even if you’re eating the exact same foods while practicing intermittent fasting, your body still undergoes changes.

It needs to learn how to work off of fat more efficiently in those caloric restricted times. A good thing, but it can have short term side effects.

Research in people switching to a ketogenic diet has found that this type of change can cause sleep issues while your body adjusts to it (4). It’s not the exact same, but a similar underlying principle that applies here.

Additionally, studies have shown that the timing of when you eat affects your circadian rhythm (which governs when you sleep) (5). If you're eating earlier or later in the day, it may be a part of your issues.

SummaryChanging eating schedules, along with needing to learn how to burn more fat for energy can cause sleep issues. The bigger the changes, the longer the adjustment period.

Fasting Windows Can Alter Caffeine Habits

This will only apply to a small number of people, but is worth mentioning.

Many people restrict caffeine intake to the morning, as it can make it harder to sleep if you consume it later in the day.

However, if you’re practicing intermittent fasting, you may not begin your eating window until later in the day. Even if you break your fast with your coffee, it may still be late enough to cause you sleep issues.

If you'd like more details, see how caffeine affects insomnia. Switching to a low-caffeine green tea may help.

Exercise Timing Can Affect Sleeping

This is a highly individual factor.

Some people sleep best if they exercise early in the day, while others like exercising later on. Typically it’s not a good idea to exercise right before bed, as most people are more likely to experience sleep trouble or insomnia right after working out.

SummaryIf fasting is making you exercise at a different time than you’re used to, it can be playing a part in your sleep difficulties. However, the body can adjust to most exercise schedules over time after the initial side effects.

Hunger and Discomfort Can Cause Sleeping Troubles

Hunger is an obvious, but common side effect of intermittent fasting, especially when you start.

It can be hard to eat the same amount of calories that you’re used to in a smaller time frame. Too large of a calorie deficit can also contribute to insomnia.

Many people with an early eating window end up not being able to eat enough calories, which leaves them hungry when it’s time to go to sleep. At the same time, eating too late can cause sleep trouble, so find a happy medium with your window.

SummaryAny discomfort makes it harder to get to sleep and maintain it throughout the night. People who struggle to eat enough calories while fasting should eat more caloric dense foods (i.e. fats), or open up their eating window until they get used to eating more.

It’s Easy to Eat More Unhealthy Food

Many people realize it’s easier to eat 2,000 calories of pizza, rather than salad or other healthy foods.

It’s also easier to justify eating junk food after fasting for a long period, particularly if you’ve exercised during it. Fasting by itself isn’t necessarily healthy if you’re not also eating healthy foods.

Once in a while is fine, but regularly eating junk food can contribute to insomnia.

SummaryEating unhealthy foods can cause sleep issues in anyone in the short term. If they are eaten on a regular basis, it can lead to vitamin and mineral deficiencies that cause sleep trouble and more serious health problems.

Fasting and Dehydration

If you’re the type to not drink a lot of water, dehydration could be an issue for you.

Many people get more of their water from food. When eaten throughout the day, this keeps them relatively hydrated.

But if you’re fasting and not drinking water by itself, you have a long period of time where your body can become dehydrated. There's a link between dehydration and insomnia.

SummaryDehydration can lead to a dry nose, throat, or mouth, and that discomfort can add to sleep issues.

Fasting Alters Sleep Cycles

Studies of people fasting during Ramadan has shown that it doesn’t affect most of your sleep cycles, but fasting does reduce the amount of REM sleep (6).

REM sleep is the lightest sleep stage (least restorative), that you generally spend more time in as the night progresses.

While not as important for basic restorative purposes, a lack of REM sleep may cause you to wake up earlier or feel less refreshed.

This isn’t necessarily a cause for concern, but can help explain a part of why your sleep experience has changed.

How To Improve Fasting Insomnia

So what can you do about all this to sleep better?

There are a few main approaches to try and mitigate the severity of your sleep difficulties:

  • Time - Being patient isn’t fun, but in most cases, people who are fasting will adapt to their new diet in 1-4 weeks.
  • Try a different eating window - Some people sleep best if they have their eating window early in the day, while others are the opposite. Experiment for at least a few days at a time.
  • Be less aggressive - Cut back on your fasting window temporarily (i.e. make it shorter) until you get used to it, and then extend it gradually.
  • Improve your sleep hygiene - Almost everyone has some poor sleep hygiene habits. If you were a good sleeper before, they weren’t as important, but now every little bit counts. Here's a complete guide to sleep hygiene for insomnia prevention.
  • Consider an over the counter sleep aid - Melatonin can make it easier to get to sleep and provide some relief while you’re adjusting.

SummaryMost importantly, if your sleep difficulties start causing you serious physical health symptoms, go see a doctor so they can help you find the root cause.

How Intermittent Fasting Can Help People With Insomnia

We’ve looked at how intermittent fasting can cause sleep issues in the short term, but in the long term it can help.

Fasting can improve insulin (and other hormones) control, which comes with a host of benefits like (7):

  • Weight loss (or healthy weight management)
  • Lower risk of diabetes
  • More stable energy levels
  • Higher levels of growth hormone

All of these lower your risk of developing insomnia in the future, and can help with deeper, more restorative sleep.

They also come with other physical health benefits, but that’s beyond the scope of this post.


  1. Effects of Total Energy Withdrawal (Fasting) on the Levels of Growth Hormone, Thyrotropin, Cortisol, Adrenaline, Noradrenaline, T4, T3, and rT3 in Healthy Males
  2. Prolonged Starvation As Treatment For Severe Obesity
  3. To Eat or to Sleep? Orexin in the Regulation of Feeding and Wakefulness
  4. Acute effects of the very low carbohydrate diet on sleep indices
  5. Fasting, circadian rhythms, and time restricted feeding in healthy lifespan
  6. The effect of intermittent fasting during Ramadan on sleep, sleepiness, cognitive function, and circadian rhythm
  7. Differences in Insulin Secretion and Sensitivity in Short-Sleep Insomnia

Medical Disclaimer: The information on is not intended to be a substitute for physician or other qualified care. We simply aim to inform people struggling with sleep issues about the nature of their condition and/or prescribed treatment.

About the authorDale is the founder of Snooze University and a sleep researcher. I overcame my sleep issues and now I'd like to help you do the same by summarizing the latest sleep studies for you.