Always consult your doctor before undertaking a new diet or fasting routine. This is not medical advice, but it is information you can use as a conversation-starter with your physician or nutritionist.
I’m currently conducting a sleep course online and there’s one thing people are asking me about A LOT: intermittent fasting. I’m not surprised. Fasting has become extremely popular as a tool for weight loss, anti-aging and longevity, and for its benefits to mental and physical health.
I’ve talked about intermittent fasting and its relationship to sleep before. Since then, there’s been some new information introduced about the ways fasting may benefit sleep. I’m guessing you might be as intrigued by this form of time-restricted eating as my students.
We’re heading right into the holidays, when healthful dietary choices can be tough, with all of those constant temptations. Eating routines—the timing of our meals throughout the day and night—also can get turned upside down, with parties, long, festive meals that stretch late into the evening, and the constant supply of snacks and treats that accompany the holiday season.
All this can take its toll on your energy levels, affect your mood, and of course make it more likely you’ll gain weight. Holiday season grazing also can create complications for sleep—even for routinely good sleepers.
You may not choose to try intermittent fasting during the holidays—I get it. But it’s worth a reminder, as we enter the season, that paying attention not only to the WHAT of your diet, but also the WHEN, matters for sleep, as well as for your mood, cognitive performance, and overall health.
What is intermittent fasting?
When you practice intermittent fasting, you designate regular, specific times to eat nothing, or to consume very few calories. When your body goes into a fasting mode, your digestive system quiets. Your body uses this time to repair and restore itself at a cellular level. Fasting also triggers the body to use its stored fat for energy, making it a potentially effective strategy for weight loss.
The period of nightly sleep is a natural fast we undertake every night, most of us without even realizing that’s what we’re doing. Indeed, a waking fasting state and a sleep state share several characteristics, including a body with cells engaged in repair, and a body that is taking a rest from the demanding work of digestion.
How does intermittent fasting work?
Creating a fasting routine isn’t complicated. (But you should always talk with your doctor about making changes to your diet, and before you begin a fasting regimen.) There are a number of routines that are commonly used with intermittent fasting.
- People choose to restrict their eating to periods of 6, 8, or 10 hours a day allows for a consistent fast to occur every day in the remaining 14-18 hours.
- Some people undertake a full 24-hour fast one or two days a week (they drink water)
- A routine known as 5:2 fasting combines single days of calorie restriction (eating around 500 calories) every 2-3 days, with normal eating in between.
It’s worth noting that despite all the attention it’s getting, fasting isn’t a new practice. People have used fasting for thousands of years as a cultural, religious, spiritual and health practice. For example, fasting that aligns with circadian rhythms–restricting eating with sundown and resuming after sunrise—is a practice that Muslims undertake during the holiday Ramadan. (Scientists have used Ramadan as a way to study how fasting affects the body and mind, as well as to study how fasting affects sleep patterns.) People of the Jewish faith fast for 24 hours during the holiday of Yom Kippur.
The health benefits of fasting
A growing body of research shows the potential benefits for health and disease protection from intermittent fasting. Fasting can result in weight loss, according to research. Studies show fasting can improve insulin sensitivity, lower inflammation, and improve markers for heart disease including lowering levels of unhealthful LDL cholesterol. Intermittent fasting has been shown to have the potential to treat some cancers, as well as neurodegenerative diseases such as Alzheimer’s and Parkinson’s. There’s also evidence that fasting may help reduce risk for developing cancer.
Time restricted eating can improve immune function and enhance the body’s ability to repair cells and DNA. Fasting induces a cellular process known as autophagy, which is when the cells of the body clears itself of damaged cells, spurring the growth of new, healthy cells. Autophagy is one way the body maintains more youthful, functional cells and protects against disease, by eliminating aged cells that behave dysfunctionally, and clearing the body of toxins that build up in older cells.
Intermittent fasting increases the body’s natural production of human growth hormone. Human growth hormone encourages fat burning and protects lean muscle mass, aids in cellular repair, and may help to slow aging. Fasting can reduce unhealthful inflammation and boost the body’s ability to protect itself against oxidative stress, which is one significant contributor to aging and disease.
Given these benefits, it’s not hard to understand why intermittent fasting would be attractive as an anti-aging strategy. But what about your nightly rest? How does fasting help improve sleep?
The science of fasting and sleep
Eating and sleeping are two fundamental processes that are also deeply entwined. Both are essential for survival. Both are regulated by internal, homeostatic drives and also by circadian rhythms. Many people know circadian rhythms play a big role in regulating sleep. But eating, hunger and digestion have their own circadian rhythmicity.
Eating and sleeping aren’t just influenced by circadian rhythms. They also exert influences back on those rhythms themselves. An irregular sleeping routine can de-synchronize a well-timed circadian clock, and throw daily rhythms off course. The timing of meals also affects our circadian clocks, and the function of circadian rhythms that exert a powerful influence over our sleep.
(If you’re interested in learning more about the WHEN of eating, including the benefits of establishing daily windows of eating and fasting times, I talk about this in my book, The Power of When.)
A growing body of research indicates fasting has a strengthening effect on circadian rhythms, helping to keep circadian clocks synchronized. Because circadian rhythms exert a strong influence over nearly all the body’s processes (as well as most of our behavior), a more robust, synchronized clock has profound effects on health. Well synchronized clocks support healthy metabolic activity, stronger immunity, and better, more restful and restorative sleep-wake cycles. Disrupted circadian clocks are closely linked to aging and disease. Keeping the body’s master bio clock in sync is one critical way to slow biological aging and potentially extend lifespan.
Other recent research has demonstrated effects that fasting can have directly on sleep, and also on conditions that affect sleep. For example, one study in mice found that a 24-hour fasting period, followed by a meal, led to deeper levels of non-REM sleep. Research has shown that fasting may help to reduce chronic pain, elevate mood and decrease inflammation—all conditions to which improvements will also benefit sleep.
A lot of people turn to intermittent fasting and to calorie restriction as a means to lose weight. Studies indicate periodic fasting can help with weight loss, including helping to push beyond a weight loss plateau. It’s important to note that research—including this 2018 study—show that even when fasting doesn’t lead to weight loss, it can improve underlying cardiometabolic health, increasing insulin sensitivity, reducing blood pressure and cholesterol, lowering inflammation, bringing appetite under control (including reducing cravings for sugar). Maintaining a healthy weight, protecting cardiometabolic health, and adhering to a healthful diet will all translate into more restful, plentiful, high quality sleep.
A group of recent studies reinforces that the timing of when we fast matters, with restricting eating to earlier in the day showing a range of benefits, from better insulin function and lower blood pressure, greater appetite control, increased fat loss and weight reduction, and better reinforcement of circadian rhythms. This lines up with all we know about the hazards of late-in-the-day eating for weight, health, and sleep. An abundance of research tells us that eating heavily near bedtime can worsen sleep quality and cause other complications for restful sleep. A 2019 study found that among people with mild and moderate sleep apnea, eating more of total calories later in the day is linked to more disrupted sleep patterns, and to more severe sleep apnea.
Individual chronotype will play a factor in determining the right window of time to schedule fasting periods. It’s not likely that Wolves will be able to sustain a fast that ENDS at 5 p.m., for example. As a Wolf and Intermittent Faster I shifted my feeding time to 5:00 p.m. and it has worked extremely well. To be clear, this is NOT a schedule for everyone, but for some Wolves, it could be a game changer.
Every chronotype is different and every individual is different. It’s worth keeping in mind the science on the benefits of early time-restricted eating, while also making room to find the intermittent fasting schedule that suits your chronotype and individual needs, in consultation with your doctor.
Don’t know your chronotype? Take this quiz to find out: http://www.chronoquiz.com/
There is a lot of interesting and compelling research coming out about intermittent fasting, and some of it shows that fasting may have real promise as a tool to help optimize sleep. But we’re still at a relative beginning of understanding how different forms of fasting and calorie restriction affect sleep. Both potential benefits and drawbacks need to be more fully examined and understood. For example, there’s evidence that during fasting periods, alertness and the production of neurochemicals that stimulate wakefulness in the brain increase. Alertness and wake-promoting hormone production appear to decrease during the night to levels that support sleep. But this is just one area of study that needs additional attention. We need to see more research that investigates the specific implications of intermittent fasting directly on sleep.
Fasting isn’t for everyone. People with histories of disordered eating are cautioned against fasting. Women who are pregnant or breast feeding shouldn’t’ fast. Anyone with any medical condition—including a sleep disorder, or mood disorders such as anxiety—should consult with a physician before adopting a fasting routine. Healthy folks, too: if you’re going to try intermittent fasting, it’s important to check in with your doctor before you begin.
If you’re interested in learning more about how intermittent fasting works and how people begin a fasting practice, there are a couple of beginner guides that I recommend as a starting point for information gathering before you talk with your physician. MindBodyGreen has a good intermittent fasting discussion here. And here’s another fasting 101 guide with some helpful basic information. Both have been reviewed by medical professionals.
Whether you explore fasting as a practice with the guidance of your doctor, or begin to pay more mindful attention to your daily eating patterns, a greater awareness of the when of your eating will make you feel and sleep better, right through the holidays and beyond.
Michael J. Breus, PhD, DABSM
The Sleep Doctor™