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Circadian Rhythm Fasting: The Full Guide On Circadian Fast

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What Is Circadian Rhythm Fasting | Benefits of Circadian Fast | How Is Circadian Rhythm Fasting Different From Intermittent Fasting

Obesity and Eating disorders have been two of the most common ailments which have plagued us in the modern world. It is a growing concern for medical professionals across the globe, as obesity and eating disorders can lead to several more serious diseases like cardiovascular diseases, diabetes, etc.

Fasting is often considered a beneficial practice for people dealing with obesity and eating disorders. Many fitness freaks advise fasting or restrictive diets to improve health. Several modern studies have proven that fasting can not only deal with several health complications but also increase life span and improve cognition.

Circadian rhythm fasting is an eating pattern in which a person can eat for a certain duration of the day and fast during the night. It is done to help the body get better aligned with the inner circadian clock of the person by eating in rhythm. 

Studies have shown that this type of eating is beneficial for people dealing with medical complications. Further, this article will try to understand the nature and benefits of circadian rhythm fasting.

What Is Circadian Rhythm Fasting?

Circadian rhythm fasting or circadian rhythm eating works with a 24-hour body clock that generally resets daily. Think of it like a master clock that signals the brain to perform certain daily activities related to the human body. 

Circadian rhythms are said to be triggered by the sun, as research has shown that the part of the brain which resets this body clock is called the hypothalamus, which is extremely sensitive to light. The sleep/wake cycle, hormone secretions, body temperature regulation, eating, and digestion can be all termed circadian rhythms.

So, what is Circadian Fasting?

Circadian rhythm fasting is a type of (time-restricted feeding) that encourages the practice of eating food at a particular time of the day. This specific window of time has not clearly been stated. However, researchers agree that it should be done in the daytime, and the window duration can be 6 to 13 hours, depending on the health of the person fasting.

Considering the duration of the body’s sleep cycle and the various hormonal activities, the ideal feeding time while practicing circadian rhythm fasting is anywhere from 8 am to 6 pm or 7 pm.

The rest of the day should be spent fasting, making it a 13 hour circadian rhythm fast. Most nutritionists call the circadian rhythm diet the “Sun Cycle Diet” since this type of diet encourages eating while the sun is out and fasting during the night. 

It is essential to point out that circadian fasting is not a “dry fast,” which essentially means that it is ok to drink water or zero-calorie drinks like water, unsweetened black coffee or tea.

circadian rhythm fasting

Benefits of Fasting Circadian Rhythm

1. Weight Loss

A circadian rhythm diet is primarily helpful for people dealing with obesity, other diet-related issues, and eating disorders. People who wish to lose weight can go for the circadian weight loss method.

Studies have shown that a person following a time restrictive diet generally tends to eat 20%-30% fewer calories than an average person. This caloric deficit results in weight loss.

Time-restricted eating diet plan limits your daily calories in a 4- to 12-hour window during the day. It has been shown to result in sustained weight loss, improvements in sleep patterns, lower blood pressure and oxidative stress markers, and increased insulin sensitivity.

2. Reduced Appetite

Most obese people who start practicing time-restrictive diets tend to have a reduced appetite. Many medical professionals believe it is due to the hormones released during the daytime, making us feel full for a more extended period.

A study suggests that meal-timing interventions facilitate weight loss by decreasing appetite rather than increasing energy expenditure. Circadian rhythm fasting may also increase fat loss by increasing fat oxidation.

3. Feeling Energised

During the morning hours of the day, the cortisol levels of the body are very high. This level again spikes during the afternoon and eventually lowers at night. In terms of melatonin, the opposite is true, as, during the daytime, melatonin levels are deficient, which rises during the nighttime, making us feel more sleepy. 

Time restrictive diets are responsible for better regulating these two enzymes, making us feel energized during the daytime and helping us sleep better at night.

4. Better Metabolism

During the daytime, the metabolic activity in our body is at its peak, especially the enzymes like ghrelin and adiponectin are in abundant quantity. Thus, food eaten during this period is better digested and metabolized well.

Research studies indicate that aligning your eating habits with the circadian clock can improve metabolic health markers and may offer a therapeutic solution to fight against metabolic diseases.

5. Better Insulin Management

The hormonal activities inside the human body are at their peak during the daytime, which eventually subsides at night. Hence it is observed that the body is better suited to deal with insulin spikes during the day.

A person practicing circadian rhythm fasting is allowed to eat during the daytime and fast during the nighttime. It prevents the body from late-night insulin spikes, primarily due to late-night eating. It can help prevent type 2 Diabetes.

6. Healthy Aging

Circadian cycles optimize the physiology and health of the cells. When it is disrupted due to bad eating habits and lifestyles, it can indirectly hamper the temporal coordination of the cells. A well-coordinated feeding-fasting cycle can significantly restore this coordination resulting in better tissue and cell health.

Other health benefits attributed to circadian rhythm fasting are reduced body fat, lower LDL (bad cholesterol) and higher HDL (good cholesterol), and reduced inflammation.

circadian rhythm fasting

How Is Circadian Rhythm Fasting Different From Intermittent Fasting?

Although at first glance, we might think that intermittent fasting and circadian rhythm diet are the same, in reality, it is not the case. However, both these kinds of diets are time restrictive. 

In the case of Intermittent Fasting, the person is allowed to choose their eating and fasting window; also, one can fast longer while practicing intermittent fasting. But in the case of circadian rhythm fasting, one has to eat during the day and fast at night. The duration of the eating period is fixed.

Most intermittent fasting programs encourage us to avoid breakfasts, but in the case of circadian rhythm fasting, you cannot skip breakfast as it is linked with the circadian cycle and should kick start your day.

Also, most circadian rhythm fasts are based on a 13-hour fasting period followed by an 11-hour eating period. Intermittent fasts mostly follow the 8:16 method, but some intermittent fasting plans encourage people to fast for an entire day (alternate day fasting).

To know more about intermittent fasting, read A Complete Guide To Intermittent Fasting + Daily Plan & Schedule

Things To Know Before Trying Circadian Rhythm Diet Plan

It is advised that before trying out any diet, it is better to take the advice of a medical health professional. Below are certain points which should be kept in mind before trying Circadian Rhythm Fasting:

  • The timings of a circadian rhythm fasting are one of the most debatable topics since we are trying to mimic the circadian cycle of our body by practicing this diet. Researchers have pointed out that the circadian cycle is linked with the hypothalamus, which is highly light-sensitive. Hence, the circadian cycle must start in the morning and end at night. So it is generally advised to eat between 8 am and 6 pm.
  • Although nothing is said about the number of calories and types of food that should be eaten while practicing any restrictive diet, we must include fruits, green vegetables, whole grains, and protein-rich foods. Foods with excess sugar should be avoided. In essence, we should think that while practicing time-restrictive diets, we tend to have lesser meal opportunities, and hence we should include nutrient-rich food in our meals.
  • Circadian rhythm fasting is not a dry fast, so water and other liquid drinks which do not spike the insulin levels in our body are allowed. Hence, it is perfectly normal to drink water or unsweetened coffee or tea while fasting. However, alcoholic drinks break the fast and should not be consumed while fasting.
  • We cannot expect results just by following any diet plan. A nutrition-rich diet must be coupled with an active lifestyle, including cardiovascular conditioning and strength training.
  • An adequate sleep cycle is one of the most important aspects of a healthy circadian cycle. It helps the body to better rest and regenerate. Experts suggest that 8 to 10 hours of quality sleep is ideal for maintaining the circadian cycle better.
  • Since blue light triggers the hypothalamus, it is advised to stay away from blue light-emitting devices like mobile phones, TV, etc., during bedtime as these can disrupt the circadian cycle of your body.


Circadian rhythm fasting can be beneficial for people struggling with obesity and diet-related ailments and to improve sleep quality.

Although most people respond positively to circadian rhythm fasting, it is essential to point out that people who are underweight or struggle to put on weight should stay away from such diets. Also, people with diabetes and metabolic diseases should consult a health professional before following this diet.

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