intermittent fasting clock plate
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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.

Fasting has become extremely popular as a tool for weight loss, anti-aging, and longevity, and for its benefits to mental and physical health.

All this can take its toll on your energy levels, affect your mood, and, of course, make it more likely you'll gain weight.

You may not choose to try intermittent fasting during the holidays โ€” 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, which 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.

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 the risk of 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 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. The 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.

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.

A growing body of research indicates that 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 the 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 โ€” 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 that periodic fasting can help with weight loss, including helping to push beyond a weight-loss plateau.

It's important to note that research โ€” including this 2018 study โ€” 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, and 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.

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.

Sweet Dreams,

Michael J. Breus, Ph.D., DABSM