Circadian Rhythm Fasting: What It Means and How to Do It

What are circadian rhythms?

Daylight saving time (DST) affects us twice a year: In the spring, we jump our clocks forward an hour, leaving us with an hour’s less sleep but more sunshine in the evenings. When DST ends in the fall, we get an extra hour of sleep, but darkness sets in much earlier.

These time changes can mess with our internal clocks, or circadian rhythms. These natural timekeepers regulate everything from energy and sleeping patterns to mood and appetite.

How do circadian rhythms work?

Our sleep/wake cycle is one of the most important circadian rhythms ‒ which are synchronized by the suprachiasmatic nucleus (SCN), located in the part of your brain called the hypothalamus. The SCN is sensitive to light, making it the most dominant influence in regulating sleep, digestion, metabolism, hormone secretion, and immunity (just to name a few).

Once we’re awake and exposed to light, our internal clock tells us to stay alert and functioning. Throughout the day, our bodies produce melatonin, a hormone that promotes sleep, and when the sun sets at night, the body starts to prepare for sleep. Shift work, sleep deprivation, blue light from electronics, and the DST adjustment can all disrupt the sleep/wake cycle ‒ and long-term circadian dysfunction can lead to mental illness, metabolic disorders, sleep disorders, immune system disorders, cancer, and even death.

Maintaining healthy circadian rhythms is essential for health, but our busy schedules and extended use of phones and computers put a strain on our bodies. The great news is that we can train our bodies to get back in sync; intermittent fasting is a part of that protocol.    

What is intermittent fasting?

Intermittent fasting (IF) continues to be a popular trend and choice for a variety of reasons, from needing support with weight loss to chronic-disease prevention. When someone practices IF, they eat only within a specific time frame. The hours in which meals can be consumed will depend on the individual, with many opting for one of the following cycles:

• 16:8 – 16 hours of fasting and eight hours of eating (e.g., fasting from 8pm to 12pm the following day and then eating between 12pm and 8pm)
• 14:10 – 14 hours of fasting and 10 hours of eating (e.g., fasting from 8pm to 10am the following day and then eating between 10am and 8pm)
• Overnight fasting ‒ 12 hours of eating, 12 hours of fasting
• 5:2 – five days spent eating whenever you want/need and two nonconsecutive days during which calories are restricted
• One meal a day (OMAD) ‒ eating just one meal per 24-hour period

Before beginning IF, you should speak with your doctor, especially if you are diabetic or hypoglycemic, have blood sugar issues, are pregnant or breastfeeding, or are recovering from an eating disorder.

Fasting begins once you finish the last meal and/or caloric beverage of the day. During the fasting hours, you can consume zero-calorie beverages like water, tea, or coffee (without added sugar or milk), since these beverages won’t spike your blood sugar.

How does fasting work?

Fasting sparks the body's ability to switch from utilizing sugar and carbohydrates to using fat as fuel, promoting fat mobilization and, ultimately, fat loss. Research has shown that fasting not only improves blood sugar levels, since the body becomes better at balancing blood sugar during fasting periods, but also decreases risk for developing diabetes and obesity.

While there’s evidence to support intermittent fasting for weight loss and general health, the jury is still out regarding the best timing sequence to achieve it. Some proponents say anything that’s 12 hours and over seems to be the sweet spot, but this doesn’t work for everyone’s schedule. Because of our bio-individuality, it’s important to find the fasting schedule that works best for your body.

Circadian rhythm fasting

As the days get shorter with the return of standard daylight hours, there’s an opportunity to implement circadian rhythm fasting, a time-restricted eating plan that involves fasting from sundown to sunrise, eating only during daylight hours. With this IF variation, the feeding cycle covers eight to 12 hours, with an emphasis on starting the day with a large breakfast. This differs from regular intermittent fasting, which allows you to choose any time during the day to eat your largest meal.

Research has shown that the timing of meals impacts metabolism and weight regulation. The University of Alabama conducted a study that showed participants who ate earlier in the day successfully lowered their insulin levels and blood pressure and had a lower overall appetite compared with participants who ate later in the day. Furthermore, eating too close to bedtime can disrupt your sleep because of indigestion as well as promote weight gain because your metabolism slows down dramatically during sleep.

The bottom line on fasting routines

One of the benefits of circadian rhythm fasting is that it takes the guesswork out of when to eat, since you can set the parameters based on your internal clock. This will help you listen to your body and find what works best for you. No matter which IF schedule you follow, eating a balanced diet is highly recommended. This includes an abundance of vegetables, lean proteins, healthy fats, and fiber as well as proper hydration. Eating foods packed with nutrients can lessen the need to snack between meals, which can help make IF easier.

If you need help with accountability, working with a Health Coach offers a nonjudgmental space to thrive and flourish in all aspects of your life, including finding the way of eating that makes you feel your best.