I.F - Intermittent Fasting and Circadian Rhythm

I.F - Intermittent Fasting and Circadian Rhythm

What's the scope on Intermittent Fasting and Circadian Rhythm?

Intermittent fasting —that is, periods of voluntary abstinence from food and drink—is an ancient practice followed in a variety of different formats by populations globally. The popular press includes numerous publications, blogs, news articles, and diet recommendations related to intermittent fasting.

There is a high level of interest in intermittent fasting and metabolic health in the scientific community, as well as among the lay public and media. In fact, an October 2016 internet search using the terms “diet fasting intermittent alternate day” had more than 210,000 hits! Google Trends (TM) has seen a steady spike in interest in this search term across the last 12 months.

6 Main Types of Intermittent Fasting

  1. 12 Hour Fasting - Keeping a solid Gap of 12 hours between 2 meals. For example, the 1st meal is at 7 am - 12-hour break - last meal at 7 pm.
    1. 16 Hour Fast - 16 hour of no food intake, 8 hours of food intake (2-3 meals)
    2. 20 Hour Fasting - This is often known as the warrior Diet - This is done by fasting for 20 hours through the day and eating 1 large meal in a 4-hour window in the evening.
    3. 24 Hour Fasting -Eating only once in a day briefly.
    4. 5:2 Fasting - 5 days of usual eating pattern and 2 days of fasting where only 500-600 calories are consumed across the course of the day.
      1. Alternate Day Fasting -Only consuming 500-600 calories across fasting days, and usual eating on an alternate day. Religious means for fasting also fit within this category.

            What about our Circadian Rhythms?

            Does eating at different times interfere with your wake and sleep cycle? Fasting at various times can and may impact your organ cycle in relation to your actual sleep and wake cycle known as the circadian rhythm.

            All cells of the human body have little inbuilt clocks, which are generally classified into either peripheral and central clocks based on their anatomical place.  The main master grandfather clock if you want to remember it by is located in the suprachiasmatic nucleus (SCN), this is our inbuilt mammalian pacemaker of the hypothalamus.

            Our Peripheral clocks are located in different organs and tissues. Both the central and peripheral clocks act to preserve the circadian rhythm of different tissue physiology via controlling "tissue-specific gene expression.” If common meal times and general want for food is shifted due to fasting and food is moved to the hours of darkness. This food intake shift partly inverts the normal circadian pattern of food intake. It's possible to assume this shift in mealtime may disrupt the circadian rhythm and biological clock of those who partake in Intermittent fasting. (1)

            Intermittent Fasting, the Circadian Rhythm and Melatonin

            The circadian rhythm is also correlated alongside melatonin. They have a direct correlation to each other, conceptual intake of surroundings plays a large impact on the secretion of melatonin in a normal sleep-wake cycle. Melatonin fluctuation is one of the most accurate markers used to investigate circadian rhythm.

            When participating in an fasting lifestyle, measuring the impact of intermittent fastings your circadian rhythm can be done by this measure for accuracy. In fact, one study on such showed some interesting results when blood melatonin was measured every 4 hours during Ramadan a common religious practice which features extensive fasting. (2) The study revealed that there was a delayed night peak and continual flattening slope on melatonin during the fasting period of Ramadan. (2)

            In summary

            It is important to note that while there have been subtle changes in melatonin, sleep and body temperature found in accordance with the fluctuation of circadian rhythm, the body does quickly adapt to eating patterns and environmental influence. The body and its intricate systems are under constant recalibration. Short term changes are not likely to throw out balance just as long term changes invokes a recalibrated adaption to the change. There is much future research to be conducted on the long term effects of fasting, Circadian Rhythms, and sleep, however it is immensely fascinating that something and autonomic as eating at times of the day can impact your body clock and something to follow closely for updates in the scientific literature on the matter.


            1  Qasrawi SO, Pandi-Perumal SR, Bahammam AS. The effect of intermittent fasting during Ramadan on sleep, sleepiness, cognitive function, and circadian rhythm. Sleep Breath. 2017;21(3):577–586.  

            2. Ramadan fasting alters endocrine and neuroendocrine circadian patterns. Meal-time as a synchronizer in humans? Bogdan A, Bouchareb B, Touitou Y Life Sci. 2001 Feb 23; 68(14):1607-15.