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#20 The importance of respecting circadian cycles

Humans function according to circadian rhythms that repeat every 24 hours and are driven by an internal biological clock that regulates metabolism and modifies our behavior according to the hours of light and darkness (the circadian cycle is what makes us active during the day and sleep at night).

Did you know that respecting circadian rhythms helps you gain health?

Rapamycin, also known as sirolimus, is a drug discovered in the 1970s with immunosuppressive properties. It was initially used in organ transplantation to prevent rejection, but was later found to have broader properties that could be beneficial to overall health.

We all have actions in common that we carry out without realizing it, such as, for example, eating breakfast in the morning because we are hungry or sleeping at night because we are sleepy. It may seem elementary, but these and many other behaviors are partly due to circadian rhythms.  

Other examples:

  • The temperature of our body during the night, before going to bed, is minimal in order to promote sleep.
  • Cortisol is necessary for the regulation of our organism and in stressful situations it is increased. First thing in the morning when we wake up, it also rises to keep us awake and alert. In addition, it is a hyperglycemic hormone and makes us have enough glucose for energy in the first hours of the morning.
  • Growth hormone is secreted in greater quantities in the early evening.
  • Melatonin is associated with maintaining and promoting sleep schedules, as it is synthesized during the night.
  • Leptin is the satiety hormone and is secreted in greater quantities during the night so that we feel satiated and do not wake up at midnight to eat.

All these functions are examples of how the body should function normally during a 24-hour cycle in which certain actions are promoted to induce an optimal state of health.

Well, these physiological responses that our organism has are given, in part, by clock genes and circadian rhythms.

We all have a circadian system that generates rhythmicity, regulates sleep patterns and eating behavior. Even so, all these patterns can be modified through our lifestyle habits, such as sleep schedule, food and sport. 

Circadian imbalance

When we do not take care of our environment and we start to chronify certain behaviors such as not sleeping enough, eating unhealthily (transgenic fats, refined and processed oils, sugars, etc.), eating at night, etc., a favorable environment will be generated to give rise to health problems and altered patterns.

Insulin and leptin resistance, overweight and/or obesity, liver alterations, dyslipidemia, alterations in intake, hypertension and inflammatory processes are some of the clearest examples.

Circadian rhythms in the digestive system

The main circadian clock is generated at the brain level, but it is not the only one. Every cell in our body has its own internal clock.

Many biological reactions that have to do with digestion are regulated and altered according to the time of day and the type of food we eat.

  • Gastric emptying and intestinal transit are faster in the morning.
  • There are hormonal differences in the intestinal tract; leptin rises at night to keep us satiated and adiponectin rises in the morning to whet our appetite.
  • Sugars are less well tolerated at night due to the lower amount of adiponectin and more fats accumulate in the blood.
  • The variation of gastric hydrochloric acid varies throughout the day, so that the predisposition to tolerate a meal better or worse will be given, in part, according to the time of ingestion. For example, there is greater acidity in the late afternoon and evening.

In this randomized crossover clinical trial on the metabolic effects of late dinner “Metabolic Effects of Late Dinner in Healthy Volunteers-A Randomized Crossover Clinical Trial” [1] and in this study published by Lopez-Minguez, J., Gómez-Abellán, P., & Garaulet, M. [2] it has been shown that late dinner is associated with alterations in metabolism and glucose homeostasis, in addition to entailing alterations in circadian rhythms.

Physical activity

Physical activity plays a fundamental role in the regulation of circadian cycles. It generates a reset in the expression of circadian genes. In people who work at night or shift work, it is important to do physical exercise to reset these biorhythms and to modulate the negative effects of having schedules contrary to the physiological ones (eating during the day and sleeping at night).

Circadian rhythms are also key to the regulation of the immune system since poor management of circadian rhythms leads to poor management of butyrate by the microbiota. Butyrate is a key short-chain fatty acid for good immunoregulation, as shown in this study “The Immunomodulatory Functions of Butyrate” [3] describing the role of Butyrate in modulating intestinal bacteria on local and systemic immunity.

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  1. Gu, C., Brereton, N., Schweitzer, A., Cotter, M., Duan, D., Børsheim, E., Wolfe, R. R., Pham, L. V., Polotsky, V. Y., & Jun, J. C. (2020). Metabolic Effects of Late Dinner in Healthy Volunteers-A Randomized Crossover Clinical Trial. The Journal of clinical endocrinology and metabolism, 105(8), 2789–2802.  
  2. Lopez-Minguez, J., Gómez-Abellán, P., & Garaulet, M. (2019). Timing of Breakfast, Lunch, and Dinner. Effects on Obesity and Metabolic Risk. Nutrients, 11(11), 2624. 
  3. Siddiqui, M. T., & Cresci, G. A. M. (2021). The Immunomodulatory Functions of Butyrate. Journal of inflammation research, 14, 6025–6041.   
  4.  Yip, W., Hughes, M. R., Li, Y., Cait, A., Hirst, M., Mohn, W. W., & McNagny, K. M. (2021). Butyrate Shapes Immune Cell Fate and Function in Allergic Asthma. Frontiers in immunology, 12, 628453


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