Circadian Rhythm Fasting: Health Benefits and How to Do It

Your circadian clock uses daylight and other cues to wake you up, ease you into sleep, and manage alertness levels.

But behind the obvious effects of the sleep-wake cycle, it influences metabolic processes and the release of hormones. These can impact your mood, energy levels, and overall health.

With circadian rhythm fasting, you make it easier for your body’s natural rhythms to run without disruptions.

Here’s what you need to know about circadian fasting and how to do it.

How do circadian rhythms work?

The circadian rhythm is a biological 24-hour cycle involving physical, behavioral, and mental changes. Your body naturally goes through this cycle every day.

Circadian rhythms regulate sleep and wakefulness, food intake, glucose metabolism, insulin sensitivity, and energy expenditure.

The body’s master circadian clock is in the hypothalamus in the brain. Cells and organs throughout the human body, such as the pancreas, contain peripheral circadian clocks.

The circadian rhythm responds strongly to light and darkness. Receptors in the retina at the back of the eye signal the hypothalamus when it’s daylight.

This makes your body awake. By contrast, darkness makes your body wind down in preparation for sleep.

Your eating schedule is the next major factor that influences your circadian rhythm. Ill-timed meals such as late-night dinners can disrupt your internal body clock through the release of the hormone insulin.

Over time, this can make your body more resistant to insulin, a major risk factor for type 2 diabetes.

Two other hormones that play a key role in circadian rhythms are cortisol and melatonin.

Cortisol normally peaks early in the morning and then again in the afternoon, giving you an energy and wakefulness boost. Melatonin, on the other hand, increases in response to darkness and promotes sleepiness.

Body temperature and circadian rhythms are also linked. The body’s internal clock increases body temperature in the afternoon, reaching a peak around 6 PM. It then lowers body temperature during the night up until around 4 AM.

Did you know? Body temperature can vary by up to 0.9ºF daily.

In the end, when and how much you eat can support or disrupt your body’s circadian rhythm. This is where circadian diet fasting comes in.

5 Benefits of the Circadian Rhythm Diet

Before you start following a circadian diet, it’s important to understand what benefits it may have. Unfortunately, as with any popular diet, there is a lot of misinformation out there.

So, what does science have to say about the advantages of the circadian rhythm diet?

#1 Improves metabolism

The time when you eat a meal can impact your metabolism, body fat percentage, and body mass index (BMI). Eating after 8 PM and taking in a higher percentage of daily calories at night could slow down your metabolism and is associated with a higher BMI.

By contrast, eating in the morning can promote positive metabolic changes. These include better blood sugar control and better nutrient absorption.

The body also uses more energy to break down a big breakfast compared to a big dinner. This, in turn, can help support a healthy metabolism that breaks down food efficiently.

The bottom line is that this diet encourages you to eat during the day and avoid late meals. By doing so, it can support and even improve metabolic health.

#2 Reduces inflammation

Eating more calories at night can increase markers of inflammation like the protein hsCRP found in the blood. This occurs independent of lifestyle factors.

In the study cited above, researchers analyzed calorie consumption in 2,650 individuals.

Their findings suggest that reducing calories eaten at night, eating more often, and fasting for longer can lower inflammation. The circadian diet promotes all of these behaviors.

Chronic inflammation may damage healthy cells and possibly lead to chronic diseases like type 2 diabetes or cancer.

#3 Lowers bad cholesterol

Findings from a 2021 study suggest that aligning eating habits with your internal master clock decreases LDL (bad) cholesterol levels while improving HDL (good) cholesterol.

These health benefits were noted in people who followed a daily eating window from 8 AM to 4 PM.

Another study investigating the effects of nighttime snacking found that the latter significantly increased total and LDL cholesterol levels.

When followed thoroughly, circadian fasting prevents late-night meals and snacking. By doing so, it can have a beneficial effect on cholesterol levels.

Tip: Help your body manage bad cholesterol by eating foods that lower cholesterol.

#4 Boosts weight loss

Circadian rhythm fasting may support weight loss in several ways.

A 2020 review article found that people sticking to a time-restricted feeding plan ate 20% fewer calories than normal. This occurred unintentionally as a consequence of food timing.

What’s more, time-restricted eating can reduce appetite in people who are overweight. At the same time, it increases fat oxidation through more efficient digestion and metabolization.

Add to this the metabolism benefits already noted, and the circadian rhythm diet looks promising for losing weight healthily.

#5 Reduces insulin resistance

Eating most of your meals in the evening increases your risk of becoming insulin resistant. This appears to occur because of disruptions in the circadian rhythms.

Insulin resistance is associated with type 2 diabetes, cardiovascular disease, obesity, and other metabolic disorders.

When cells become resistant to insulin, blood glucose levels rise. In time, this rise can become permanent.

Other research suggests that a circadian rhythm diet can help improve insulin sensitivity. It achieves this by better aligning meal times with the circadian rhythm.

For example, with circadian fasting, you don’t eat large meals in the evening.

Potential Risks of Circadian Rhythm Fasting

Fasting according to your circadian rhythm may not be healthy for everyone. Here are a few things to consider before you decide to follow this diet:

• Reduced caloric intake: Circadian rhythm fasting can significantly reduce your caloric intake. This may not be healthy if you are elderly, underweight, or train intensively.
• May complicate recovery from disordered eating: People suffering from compulsive eating or an eating disorder may struggle with circadian fasting. They need to address any underlying health disorders before embarking on this form of restrictive eating.
• Nutrient deficiency: Circadian rhythm fasting requires discipline and at least some basic nutritional knowledge. Without these, you may not consume sufficient nutrients during your daily eating window.

In the end, while circadian rhythm fasting comes with some drawbacks, these should be manageable for most people.

How to Do Circadian Rhythm Fasting

What you eat, when you eat, and how well you sleep are all important when it comes to circadian rhythm fasting. Let’s take these one at a time.

When to eat

A popular eating schedule for circadian fasting is between 8 AM and 6 PM. This follows the daylight cycle in most locations.

However, more research is needed to identify the ideal hours for circadian rhythm fasting.

The bottom line is that you should try to eat within a 10-hour period.

What to eat

The circadian rhythm diet doesn’t come with food recommendations or restrictions. That said, it’s important to eat a varied diet with plenty of fruits, vegetables, whole grains, and healthy fats.

Reduce your intake of sugar, salt, and unhealthy fats like saturated fats. A varied diet helps you take in enough nutrients so that you don’t have to rely on supplements.

You can drink water any time of the day. Water is calorie-free and won’t break your fast. But avoid drinking alcohol or sugary drinks outside of the fasting period – these have calories.

Adjust your caloric intake according to your activity levels and weight goals. Being a vegetarian or wanting to eat keto while on circadian fasting may pose challenges. It’s best to discuss this with a doctor first.

Sleep

Get at least 7 hours of sleep. This is the optimal amount of sleep for an adult, according to the American Academy of Sleep Medicine.

Skipping on sleep can disrupt your natural circadian rhythm. It can also make it difficult to stick to a 10-hour eating window.

Exercise

You can and should exercise while following a circadian rhythm diet. Regular exercise can keep you healthy and support your weight loss goals.

Aim at least for the recommended 150 minutes of moderate-intensity exercise every week.

Circadian Rhythm Fasting vs. Intermittent Fasting

Both circadian rhythm fasting and intermittent fasting are forms of time-restricted feeding.

However, circadian fasting is more restrictive in that it requires your eating window to close by 7 PM.

With intermittent fasting, you can choose your own eating window so long as you stick to a 12–16 hour fasting window. Intermittent fasting typically involves a longer fasting period of 16 hours.

Whether you eat or skip breakfast is another difference between these diets. Breakfast isn’t a key meal of the intermittent fasting diet. In fact, many people following this diet skip it.

By contrast, breakfast is a key meal of the circadian fasting schedule and the one packed with the most calories.

When on this diet, you should eat breakfast early. This coincides with the early morning cortisol peak. Cortisol increases stress levels, but eating breakfast early helps counter that.

	Circadian fasting	Intermittent fasting
Eating window	Choose your own	Eat during daylight and fast starting in the evening
Fasting period	Longer, up to 16 hours	Can be shorter, up to 12 hours
Breakfast	Skip	Eat

FAQs

Conclusion

Circadian rhythm fasting can help you shed weight while improving metabolic health, reducing inflammation, and lowering bad cholesterol.

It involves fasting for 12 hours or more and eating during daylight, getting most calories from your early meals. But the time-restricted eating plan called circadian rhythm fasting isn’t a one-size-fits-all solution to weight loss or healthy living.

Night shift work or living with a chronic disease may make this plan unsuitable for you. If you have any doubts about the circadian eating pattern, discuss this with your doctor.