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This is an article I (Alex) am currently working on but I thought I would publish this first draft as it is such an interesting topic. There is a growing interest in our circadian rhythm and how it impacts our health, in numerous ways, but also how our lifestyles influence the rhythm also. For example the science of chrononutrition explores how our nutritional habits influence our biology and circadian rhythm. Can an understanding of our circadian rhythm help us recover from chronic health conditions, or help us simply improve our health, happiness and longevity?

Circadian rhythms enable optimal energy utilization and reproduction. Virtually all aspects of human physiology (sleep-wake cycles, body temperature, hormone secretion etc.) are mapped onto 24-hour rhythms. However, modern life styles may frequently disrupt circadian rhythm.

Circadian rhythms are endogenously generated rhythms that occur with a periodicity of approximately 24 hours

The clock system is complex, and consists of the central circadian clock (“master clock”) located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus in the brain, and peripheral oscillators, which are not entirely autonomous. The SCN does not oscillate exactly over 24 hours. Therefore, it is necessary to entrain this circadian pacemaker to daily external light-dark cycle. Light is the most powerful signal regulating SCN.

In addition to light, feeding, and the availability of metabolites, represents another important and potent synchronizer for central and peripheral clocks.

The central clock that dominates activity rhythms is entrained by light/dark cycles, whereas peripheral clocks regulating local metabolic rhythms are determined by feeding/fasting cycles.

Circadian rhythms and cellular metabolism are intimately linked

Peripheral clocks dominate local physiological processes, including glucose and lipid homeostasis, hormonal secretion, xenobiotics, the immune response, and the digestion system.

Circadian clocks enable the anticipation of daily events, conferring a considerable advantage for saving time and the efficient use of energy

Evidence accumulated during recent years suggests that meal timing can affect a wide variety of physiological processes, including sleep/wake cycle, core body temperature, performance, and alertness.

Circadian Rhythm & Digestive Health

Importantly, a critical role in the clock-nutrition interplay appears to be played by the microbiota.

Disruption of circadian physiology, due to sleep disturbance or shift work, may result in various gastrointestinal diseases, such as irritable bowel syndrome, gastroesophageal reflux disease (GERD) or peptic ulcer disease.

In addition, they are at increased risk of obesity, diabetes (Pan et al., 2011), cardiovascular disease, and cancer (reviewed in Wang et al., 2011).

There is evidence that chronodisruption affects the brain-gut axis, contributing to the pathogenesis of a number of important diseases in the digestive system. Circadian oscillations affect important core functions such as gut motility, maintenance and replacement of the protective barrier (the gut lining), and immunology and production of digestive enzymes.

In terms of the association between circadian rhythms and colonic motility the following conclusions can be drawn from previous studies:

  1. colonic motility is under the influence of circadian control (maximal motility during the day, minimal during the night)
  2. components of the molecular clock have been identified in the GIT
  3. neurotransmitters expressed in the myenteric plexus (e.g., VIP) were also identified in the neurons of SCN master clock
  4. there is strong epidemiological evidence that alterations in colonic motility, due to the disruption of the molecular clock, (shift work, transmeridian flights) may have a potent impact on digestive functions

As discussed in our article (found here), poor gut motility is a key underlying mechanism in small intestine bacterial overgrowth, a frequent finding in patients with chronic fatigue syndrome. The fact that poor sleep is also a frequent finding, suggests both digestive health and sleep need to be considered/supported simultaneously when present.

Circadian Rythms & The Liver Clocks

we reveal that a high-fat diet (HFD) generates a profound reorganization of specific metabolic pathways, leading to widespread remodeling of the liver clock.

Circadian Rhythms & Nutrition – Chrononutriton

Recently, a novel field between nutrition and circadian clock system is referred as “chrononutrition”. Recent findings regarding chrononutrition, include food components that regulate circadian clocks, and meal times that affect metabolic homeostasis.

daily feeding schedules synchronize circadian oscillators in many brain regions and virtually every organ system

feeding stimulated at irregular mealtimes could result in disrupted timing of metabolic processes, with negative consequences for metabolic functioning and health

Three factors are mentioned in an article by Oike et al. (2014) that affect the circadian clock:

  • A high-fat diet causes a large-scale reorganization of oscillation in transcripts and metabolites in the liver
  • Resveratrol, a polyphenol found in red wine, resets clocks
  • Caffeine contained in food and drinks prolongs circadian locomotor rhythms

Another argument for considering chrononutrition is that in animal studies time-restricted feeding with a high-fat diet without caloric reduction suppresses obesity and metabolic diseases.

Unpredictable feeding times might disturb the circadian harmonization of metabolic processes beyond organs and finally disrupt energy homeostasis

Research has also investigated circadian control of oscillations in mitochondrial rate-limiting enzymes and nutrient utilization. Mitochondria are the energy production factories of the cell and mitochondrial dysfunction is frequently seen in patients with chronic fatigue syndrome. The authors Neufeld-Cohen et al. (2015) concluded:

It, thus, seems that changes in feeding time or food composition are sufficient to alter mitochondrial composition and hence, function.

So, it appears that feeding time has a dramatic effect on health and can be employed to prevent obesity and various other metabolic pathologies. Hence, ‘‘chrono-nutrition’’ refers to food administration in coordination with the body’s daily rhythms. This concept reflects the basic idea that, in addition to the amount and content of food, the time of ingestion is also critical for the well-being of an organism.

Glucose Regulation

in healthy humans, plasma glucose excursions after identical meals are higher at night than in the morning

In addition to glucose production, glucose uptake by various tissues shows daily rhythmicity as well

Taken together, it is obvious that the circadian timing system strongly influences virtually all aspects of glucose metabolism

The Adrenal Glands & Cortisol

It is widely accepted that the daily GC rhythm is also under the control of circadian timing because its rhythmicity is completely blunted by disruption of the SCN harboring the master oscillator. It is well known that chronic dysregulation of GC, i.e. either hyper- or hyposecretion, induces the onset of diverse pathological conditions by disrupting carbohydrate and lipid metabolism, immune response, cardiovascular activity, mood, and cognitive/brain functions. A growing body of evidence suggests that not only the level of circulating GC but also its rhythmic activity plays a significant role in human health and disease (Chung e al., 2011).

Blue Light

Peripheral clocks also show an autonomic cycle of approximately (but not exactly) 24 h (Brown et al., 2008; Yamazaki et al., 2000) that needs synchronization with the external light–dark cycle.

I recommend these glasses that may not only provide relief from bright light during the day (many people with CFS are sensitive to light) but they will also block the blue light from electrical devices which has been shown to effect melatonin production and thus interfere with sleep.

melatonin may have a role in synchronizing peripheral clocks as well (Torres-Farfan et al., 2006; Valenzuela et al., 2008).

Circadian Rhythm in Chronic Fatigue Syndrome

Sleep disturbances are common in chronic fatigue syndrome and may act as a perpetuator of some of the other imbalances frequently present, such as irritable bowel syndrome. Considering how we can optimise circadian rhythms through dietary and lifestyle strategies may be an important part of the process.


Circadian clocks in animals are tightly connected to energy homeostasis and are affected by feeding time as well as food composition/components. Clocks control energy metabolism and metabolic states influence clocks. The prevalence of metabolic diseases has increased in many countries where circadian behaviors, including meal times, can be disrupted and individuals can be deprived of sleep.

Time-restricted feeding or a balanced breakfast can powerfully entrain and thus amplify circadian clocks in peripheral tissues, whereas feeding at unusual times or with a high-fat diet attenuates these clocks.

Light/dark cues are also important to maintain cooperation between circadian systems and energy homeostasis through the central clock.

Consideration of appropriate meal times is one wise way to control metabolic diseases even without caloric reduction. The consumption of beneficial food components, such as polyphenols, unsaturated fatty acids, and fiber, at suitable times would help to promote health in the same way as medication is administered at specific times in chronopharmacology.

Not only the quality and quantity but also timing is important for nutrition.

Based on these studies, we believe that maintaining a regular food intake schedule can help maintain human health.

An interesting article to read can be found here.

Listen to this podcast on nutrient timing and circadian rhythms here.


Neufeld-Cohen et al., (2015) Circadian control of oscillations in mitochondrial rate-limiting enzymes and nutrient utilization by PERIOD proteins, PNAS

Oike et al., (2014) Nutrients, Clock Genes, and Chrononutrition, Curr Nutr Rep; 3:204–212

Konturek et al. (2011) Gut clock: Implication of circadian rhythms in the gastrointestinal tract, Jounral of Physiology and Pharmacology; 62, 2, 139-150

Tahara & Shibata (2013) Neuroscience Forefront Review Chronobiology and Nutrition, Neuroscience 253, 78–88