What Is Intermittent Fasting, and Will It Help Your Sleep?
Fasting—an ancient practice that’s new again.
Posted Apr 11, 2019
Last week, I talked about two very popular diets — Paleo and Keto — and how adopting these eating plans might impact your sleep.
There’s another eating strategy that’s increasingly popular these days and has its own unique relationship to sleep: intermittent fasting.
Incorporating fasting into a regular routine is popular among people looking to lose weight and improve their metabolic health. It’s also used by people seeking to sharpen their cognitive skills and slow the aging process.
Fasting—an ancient practice that’s new again
Fasting has an ancient history as a cultural, religious, spiritual and health practice. It’s become very popular in recent years as a tool for weight loss, anti-aging, and longevity, and for its benefits to mental and physical health. Intermittent fasting isn’t about what you eat. It’s about when.
(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.)
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 an effective strategy for weight loss.
How intermittent fasting works: People use different patterns of eating and non-eating to fast as part of their regular lives. Confining eating to 8, 10 or 12 hours a day allows for a consistent fast to occur every day in the remaining 14-16 hours. Some people use a 24-hour fast one or two days a week. Others opt for a day of significant calorie restriction (around 500 calories) every 2-3 days, with normal eating in between. This is often called 5:2 fasting.
The health benefits of fasting
In today’s society, our relationship with food is different than at any other time in human history. As humans, we evolved over many thousands of years with food as a scarce resource. In our modern world, there exist food shortages and food scarcity that are serious, unacceptable societal health issues, in the U.S. and around the world. But for many millions of us, it’s overconsumption of food—both in quantity and in the timing of our eating—that poses a serious threat to health. Obesity, type 2 diabetes, cardiovascular disease: These and other chronic illnesses are connected to diet and eating habits.
Healthy sleep can also be compromised by overeating and eating at the wrong times. Research shows that eating heavily near bedtime can worsen sleep quality, making sleep more restless and less refreshing. The timing of meals also affects our circadian clocks and the functioning of circadian rhythms that exert a powerful influence over our sleep and health.
A growing body of research shows the potential benefits for health and disease protection from intermittent fasting. Research shows that fasting can result in weight loss. Research also shows fasting can improve insulin sensitivity, lower inflammation, and improve markers for heart disease including lowering levels of unhealthful LDL cholesterol. Intermittent fasting has shown promise as in offering protection against and treating some cancers, as well as neurodegenerative diseases such as Alzheimer’s and Parkinson’s.
Studies show intermittent fasting strengthens immune function and enhances the body’s ability to repair cells and DNA. Natural production of human growth hormone appears to rise dramatically in connection with intermittent fasting. Human growth hormone encourages burning of fat and maintenance of lean muscle mass, aids in cellular repair, and may help slow the aging process. And fasting can reduce unhealthful inflammation and boost the body’s ability to protect itself against oxidative stress, which is a major contributor to aging and disease.
The science of fasting and sleep
A quiet digestive system, a body in repair mode, a stretch of not eating? If this description of the benefits of sounds a bit like sleep mode, you’re right on! Healthy, typical sleep is a natural period of daily fasting.
Routine fasting in many ways helps the body stay well aligned for sleep. Eating during the evenings, and having a body engaged in active digestion, often create problems for sleep. Studies show restricting eating to 8- or 12-hour windows can help us maintain healthy body weight and avoid high blood sugar, insulin resistance, and diabetes—regardless of the nutrient breakdown of the food we eat within those windows.
Time-restricted eating also can strengthen our 24-hour circadian clocks, which exert a dominating influence on our sleep. A stronger, more synchronized circadian clock means an easier time falling asleep, staying asleep, and waking feeling refreshed on a regular basis. That combination of consistency and quality in a sleep routine is what we all want, to help us feel and function at our best, and to protect our health over time, and with age.
The timing and duration of fasting can influence how it affects sleep. Some studies suggest that periodic, short-term fasting can improve sleep. One study found fasting periodically reduced awakenings during the night and decreased leg movements (which can be highly disruptive to sound sleep). Other research has shown that fasting may decrease REM sleep.
I have a number of patients to practice intermittent fasting and find it’s been helpful to their sleep as well as their waking performance. Most of them find it relatively easy to adjust to a fasting state without intense, disruptive urges to eat. Still, people may experience more cravings and prolonged hunger when fasting for a full day. It can be difficult to fall asleep when you’re very hungry. That’s one factor that may have an impact on how fasting affects your nightly rest.
The impact of fasting likely depends on this individual response, as well as on the specifics of the fast itself, including how long it lasts. We need to see more research about the long-term effects of fasting to circadian rhythms, sleep and other aspects of health. Allowing for at least 12 hours of eating-restricted time daily is one of the most manageable ways to incorporate a form of intermittent fasting to your routine.
How to sleep well when fasting
Listen to your body. Studies can tell us a lot about the impact of diet on our sleep. But no amount of research tells us everything. How our individual sleep responds to different eating plans will vary from person to person. Restricting eating after sundown may bring new soundness to your sleep, while a 24-hour fast leaves you agitated at bedtime.
Sleep needs are individual; so are our responses to diet and time-restricted eating. We often need to tweak our bedtimes and wake-times to find the optimal sleep window. Similarly, we often need to fine-tune our eating patterns to achieve optimal eating and fasting routine. Accepting and working with your individual reactions to fasting—reactions that can be physical, as well as mental and emotional—is one way to make this eating strategy work for you, not only during the day but also at bedtime.
Stay hydrated. Drinking plenty of water throughout the day will help will hunger cravings, mental focus, mood, and energy when you’re practicing intermittent fasting or time-restricted eating. Staying hydrated will also help you sleep more soundly at night. Even minor dehydration can cause restless sleep, and increase your risk of snoring—thanks to a dry mouth, nose, and throat.
Make meals count. The patients I have who practice intermittent fasting tell me they’re surprised at how quickly they’re bodies adjust to periodic restrictions on their eating. Most say their hunger cravings subside pretty quickly, and they don’t find themselves wanting to overeat, or indulge in lots of unhealthful “treat” foods, during their non-fasting times.
You’ll get the greatest benefits from fasting if you maintain a healthy diet during non-fasting times. Limit sugar and processed foods and focus on whole foods, plenty of fiber, lots of vegetables and fruits, lean proteins like fish, and healthy fats from nuts and high-quality oils. These healthy staples will give your body the nutrients it needs and bolster your energy throughout the day. You’ll also sleep better.
Be mindful. A number of my patients also tell me they’ve discovered that time-restricted eating and intermittent fasting has helped them become more mindful. Practicing mindfulness can also help you fast more comfortably, get through temporary cravings, and keep a healthy diet on track. Studies show mindfulness can help us make better food choices. And there’s a robust body of research that shows mindfulness practices improve our sleep. Practicing mindfulness isn’t complicated: it’s as simple as slow, thoughtful breathing or a simple moving meditation.