Impact of Intermittent Fasting on Sleep

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Sleep is an essential part of everyone’s life.

No matter what you do or how much you work, you need at least 7 hours of high-quality and efficient sleep when the night comes.

Sleep is for life.

However, only some have the privilege of collecting adequate sleep throughout the nighttime and feeling refreshed when the morning alarm goes off. Stress, fatigue, a poor environment, and, most importantly, irregular eating habits all affect sleep.

But what if we can modify our dietary patterns to make them more efficient for our sleeping rhythm? A recent study by the Department of Kinesiology and Nutrition at the University of Illinois in Chicago, USA, has found a relationship between intermittent fasting and sleep.

Is there an extra benefit of fasting beyond what we know? Read on to find out.


Elucidating the Connection Between Intermittent Fasting and Sleep

What Is Intermittent Fasting?

Intermittent fasting is an eating plan which restricts your eating time to 4 to 8 hours a day.

Typically, we consume 3 meals per day: breakfast, lunch, and dinner. So, for example, if you have breakfast at about 8 AM each day, then the last meal of the day will likely be at 6 PM. That’s 10 hours of eating time. What’s good about this typical eating pattern is that you take in food throughout the day and get sufficient energy for everyday activities.

However, what’s not optimal is your insulin levels – the hormone secreted in your pancreas to reduce your blood sugar levels – tend to spike more frequently, if not all day, to work in response to food intake. Unfortunately, frequent increase in insulin is essentially detrimental, as it increases the risk of insulin resistance – a common hallmark of diabetes.

This hypothesis does not imply that a 3-meal eating pattern causes diabetes. But if you’re genetically predisposed and consume excessive food daily, the risk of diabetes is higher.

That’s why intermittent fasting emerges to solve this problem.

Intermittent fasting focuses on the time window when you can consume food rather than what type or amount of food. Still, some particular methods may also work with caloric restriction for more profound benefits.

On an adherence difficulty scale, some well-studied intermittent fasting schedules include:

16:88 hours of eating followed by 16 hours of fasting
20:44 hours of eating followed by 20 hours of fasting
5:22 days of fasting interspersed between 5 days of eating; 20% of regular caloric intake on fasting days is acceptable
Alternate-day1 day of fasting followed by 1 day of eating; 500 calories on fasting days is acceptable


How Does Intermittent Fasting Work?

As the name suggests, intermittent fasting works by making your eating schedule a discontinuous process.

Unlike popular belief, condensing your meals is more important than you think. For example, if consumed within 4 to 8 hours, the same amount of calories will have different effects on the body than a 10- to 12-hour period.

Below are the levels of blood glucose and insulin in the human body during a typical eating day with three meals. Both glucose and insulin increase significantly at least 3 times daily, which correlates with the number of meals. This positive association means the body has very little time when either glucose or insulin is low.

The fluctuation of blood glucose (red) and insulin (blue) during a day with three meals. Source: The American Journal of Clinical Nutrition.
The fluctuation of blood glucose (red) and insulin (blue) during a day with three meals. Source: The American Journal of Clinical Nutrition.


The bigger problem is that blood glucose can reach over 100 mg/dL after meals, which is equal to prediabetic levels. If this fluctuation is persistent, the body must go through multiple times within a day when the glucose level is abnormal.

Intermittent fasting shrinks the glucose-insulin fluctuation within as little time as possible, making room for a more stable condition inside the body – also known as homeostasis. However, depending on the duration and methods, the effects vary, with higher adherence and difficulty resulting in extra benefits.


Intermittent Fasting Benefits in General


Due to its significant impact on metabolic parameters, in which glucose and insulin levels undergo the most critical changes, intermittent fasting can result in a vast array of benefits in metabolic health, including:

  • Assist in weight loss & fat loss
  • Lower blood glucose & insulin levels
  • Decrease blood pressure & cholesterol levels
  • Prevent insulin resistance & increase insulin sensitivity
  • Reduce the risk of diabetes & obesity
  • Help detoxify the digestive system
  • Fight against inflammation


Other functional effects of intermittent fasting on various organ systems. Source: The Obesity Society.
Other functional effects of intermittent fasting on various organ systems. Source: The Obesity Society.


Intermittent Fasting and Sleep: Is There a Connection?

Still, it wasn’t until recently that scientists started to look into the impact of fasting on sleep.

Many agree with the hypothesis that by lowering glucose and insulin levels and reducing body weight, intermittent fasting increases the quality and efficiency of sleep. Indeed, overweight and obese individuals have a higher risk of sleep apnea, which blocks the airway and causes temporary cessation of breathing.

Many others suggest that intermittent fasting may improve sleep quality by correcting our circadian rhythm. We all have suffered from nights of restlessness as we have consumed too much food before sleep. Intermittent fasting limits food intake during nighttime, restoring the nature of our internal clock and facilitating our sleeping patterns.

Suppose our sleep efficiency is measured by the quality, duration, latency, and risk of apnea. How much does intermittent fasting affect it?


Effects of Intermittent Fasting on Body Weight

According to research by the University of Illinois, if a person loses 5% to 10% of his baseline body weight, sleep will improve, and the more weight is reduced, the better the sleep.

Scientists have a clue when hypothesizing that weight loss due to intermittent fasting has a connection to sleep since obesity is associated with decreased sleep duration, poor sleep quality, insomnia, sleep disturbances, and daytime sleepiness.

After reviewing all possible studies on intermittent fasting, scientists found that this eating pattern results in modest to significant weight loss of 1% to 7% within 12 to 16 weeks. This outcome complies with the degree of weight loss needed to improve sleep (5% to 10%), so scientists moved further by examining the sleep parameters.


Effects of Intermittent Fasting on Sleep Parameters

Sleep Quality
StudiesMethodsMeasurement ToolsFindings
Wilkinson, M. et al.12 weeks of time-restricted eatingThe myCircadianClock (mCC) smartphone appIncrease by 23% in nightly restful sleep
Kestyus, D. et al.12 weeks of time-restricted eatingVisual analog scale (VAS)Sleep quality improved by 10 points (from 65 to 75 out of 100)
Kalam, F. et al.12 weeks of alternate-day fastingPittsburgh Sleep Quality Index (PSQI)Sleep quality improved, although the effect diminished by week 24


Sleep Duration
StudiesMethodsMeasurement ToolsFindings
Gill, S. & Panda, S.16 weeks of time-restricted eatingSelf-assessment survey

(increased minutes are not specified)

Sleep duration improves by 1.5 points on a scale of 10.


Sleep Latency
StudiesMethodsMeasurement ToolsFindings
Wilkinson, M. et al.12 weeks of time-restricted eatingA wrist device to track sleep efficiencyNo change
Cienfuegos, S. et al. 8 weeks of time-restricted eatingPittsburgh Sleep Quality Index (PSQI)No change
Parr, E. et al.4 weeks of time-restricted eatingNo change


Sleep Apnea Risk
StudiesMethodsMeasurement ToolsFindings
Cienfuegos, S. et al. 8 weeks of time-restricted eatingThe Berlin Questionnaire (a self-report survey that identifies sleep apnea)Sleep apnea risk decreased from 47% to 20% (weight loss was minimal at 3%)
Kalam, F. et al.12 weeks of alternate-day fastingNo significant decrease in the risk of sleep apnea despite a 6% of weight loss


Conclusion: Intermittent fasting and sleep have a positive correlation.

Depending on the methods, sleep quality, duration, and sleep apnea risk may improve. Nevertheless, improvement in sleep latency is not observable. Notably, the effects depend more on the course of adherence rather than the distribution of the eating-fasting window.


Can Intermittent Fasting Make It Hard to Sleep?


Although the University of Illinois study concluded that intermittent fasting did not have any detrimental effects on sleep, this eating pattern may make sleep more difficult.

If you implement intermittent fasting by consuming food at irregular intervals, you may disrupt your circadian rhythm and cause unwanted changes in your temperature, digestion, and mood. For example, having a meal too close to bedtime (less than 3 hours) may increase your body temperature and the activity of your digestive system.

On top of it, heavy meals due to a concentration of food within a short time may also cause upset stomach, including:

  • Acid reflux
  • Nausea & vomiting
  • Gas & bloating


Unnatural eating patterns can also throw off your circadian clock, leaving you feeling sleepy during the day and awake at night. Finally, fasting can affect your sleep hormone melatonin and stress hormone cortisol, both of which regulate your sleep.

So, we can say that the connection between intermittent fasting and sleep is like a “double-edged sword.” If you do it right, intermittent fasting enhances your sleep. Otherwise, your sleep problems may even further escalate.


What to Consider About Intermittent Fasting

Find a Fasting Method That Works

Choose the method that works best for you. Remember that complying with a plan longer is more important than sticking to a more difficult one.

If you’re a beginner, start with the 16:8 diet, meaning 8 hours of eating and 16 hours of fasting. This diet is easy because you can do it simply by skipping your breakfast. So eat your first meal at 11 AM and the last at 7 PM, and you’re already fasting.

As you’re adapting, try cutting your daily calories gradually from 20% to 30% or working your way up to a more extreme diet – the 20:4. This plan is even better for your sleep as it gives you enough time to digest your last meal of the day and stabilize your homeostasis.

The 5:2 and the alternate-day fasting are the most complicated plans, so only implement them as you’ve fully adjusted your body to regular fasting. Most people don’t adhere to them long-term due to their difficulty. Moreover, most studies about them only last 12 weeks or less, so a maximum duration of 12 weeks is sufficient.


Avoid Heavy Meals at Bedtime

Eat your last meal of the day at least 3 hours before bedtime. Also, avoid heavy meals or foods that are hard to digest, like fatty foods.

Any meal that is very filling counts as a heavy meal. It fills you up and makes you want to sit or lay down for an hour without moving. Don’t let your food cravings at the end of a fasting day stop you from reaching your goal and improving your sleep. Indulging yourself in a feast will only leave you tossing and turning all night.


Create a Fixed Eat-sleep Routine

Finally, adhere to a routine that stays unchanged throughout the whole process.

If you’ve decided that your first meal starts at 11 AM and the last one at 7 PM, keep it like that until you’ve reached your goal or want to switch to another plan. Any sudden change in your eat-sleep routine will disrupt your circadian rhythm and, consequently, your sleep.

Below is a detailed 6-month intermittent fasting plan to improve your sleep:

TimelineMethodsDaily Caloric IntakePhysical Activity Levels
Month 116:8Maintain regular daily caloric intakeRegular training; at least 150 minutes/week; moderate intensity;

combine cardio with muscle strengthening.

Month 216:8Cut back 20%-30% of daily caloric intake
Month 320:4Maintain regular daily caloric intakeLess training; at least 75 minutes/week; moderate to low intensity; combine cardio with muscle strengthening.
Month 420:4Cut back 10% of daily caloric intake
Month 55:2 or alternate-day20% of regular caloric intake or 500 calories on fasting days; eat as you desire on non-fasting daysNo training on fasting days. Low-intensity training on non-fasting days; 75 minutes/week; only cardio.
Month 65:2 or alternate-day



McStay, M. et al. (2021). Intermittent Fasting and Sleep: A Review of Human Trials.


If you have questions about fasting and sleep or any health problems discussed here, connect with us and learn more. 

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