Intermittent Fasting and Circadian Rhythm Explained

Anyone who promotes intermittent fasting (IF) can choose a comfortable eating and abstinence from food range by adjusting it to their daily routine and occupation. However, in accordance with the principles of proper nutrition and human physiology, the timing of nutrition and abstinence from food is essential to ensure proper metabolism and overall human health.

Current research emphasizes the importance and direct relationship between IF and circadian rhythms (CR). Fasting, eating time, and sleep interact with each other and influence the circadian rhythms of various organs and cells in the body (Almeneessier, Pandi-Perumal, BaHammam, 2018).

What is circadian rhythm and its impact on our bodies?

The endogenous circadian clock in living organisms ensures that physiological processes take place at the optimal time for the body. The time of day has been found to play a crucial role in metabolic, energy and physiological processes.

Based on research, it has been hypothesized that IF, CR, lifestyle (diet, sleep, physical activity), gastrointestinal microbiota activity, and diversity have a direct impact on human metabolic processes associated with chronic diseases such as obesity, type 2 diabetes, cardiovascular disease, the development or exacerbation of certain cancers (Patterson et al., 2015).

The picture down below shows the effects of the human circadian clock on metabolism and physiological processes.

How does a circadian rhythm work?

The human circadian clock has been found to be in the hypothalamic nucleus, which is stimulated by light and darkness (Patterson et al., 2015). Research shows that each cell in the body also has individual CR in peripheral tissues.

Some starvation regimens, food abstinence, eating time, and sleep influence fluctuations in circadian clock gene expression that activate molecular mechanisms of energy metabolism and improve metabolic processes (Patterson et al., 2015). 

According to the theory of circadian rhythms, human metabolism is most active during the day and begins to slow down between 6-7 pm after the production of melatonin (a hormone that regulates the body’s resting regime) begins.

During the day/diet phase, when insulin secretion, fatty acid synthesis, bile acid secretion, and other metabolic reactions take place, all necessary nutrients must be consumed, allowing the body to rest and absorb all nutrients during the evening and night.

Most research demonstrating the influence of nutrients and eating time on CR has been conducted in animals. However, analysis of the scientific literature and research on night work with humans has shown that night work disrupts the human circadian rhythm and is associated with an increased risk of obesity, diabetes, cardiovascular disease, and certain cancers (Grundy et al., 2013).

Studies in people who observed religious fasting in Ramadan, when not eaten or drunk for one month from dawn to sunset, have shown that Ramadan causes a delay in the circadian rhythm of core body temperature and hormone secretion (Almeneessier, BaHammam, 2018). However, more detailed research is needed to elucidate the long-term effects on human circadian rhythms.

It is well known that in humans, even a single food abstinence interval (18–19 hours, including night time) can reduce concentrations of metabolic biomarkers associated with chronic diseases (Patterson et al., 2015). The theory is followed worldwide and patients are asked to abstain from food for 8 to 12 hours before performing thorough blood tests to achieve a constant level of metabolism and other blood parameters.

The Bottom Line

In line with human metabolic and physiological processes, more in-depth human research is essential to determine whether regular IF combined with circadian rhythm theory can provide a viable and sustainable dietary strategy that improves metabolic and physiological processes and reduces the risk of developing chronic diseases.

Research also shows that a combination of IF methods and CR theory can achieve more effective and long-lasting results in reducing body weight in obese or overweight patients compared to a standard hypocaloric diet. It is believed that the combination of CR and IF methods should be applied to a wider range of patients as an appropriate treatment for obesity.