The human body is such a beautiful and stunning machine that is designed to adapt very efficiently to its constantly changing environment. Humans have muscles that will grow and strengthen when exercised, metabolism that will slow down and speed up according to food availability, and most importantly a circadian rhythm that is designed to anticipate and prepare for changes in the external environment.
The circadian rhythm is also known more commonly as the “biological clock”. Our biological clock is a combination of complex systems inside the human body that work together in synchronization to make internal changes (metabolically, psychologically, behaviorally, etc.) at specific times of the day to predict and prepare for external changes that will occur in the environment so our body can respond and function appropriately. This article will go deep into the understandings and complexities of the circadian rhythm and its role in our body and the adverse effects circadian disruption can cause. A lot of scientific research has found that chronodisruption is associated with obesity and metabolic syndrome symptoms as well as premature aging, cancer, cardiovascular disease and psychological problems. After reading this article, one will easily understand why.
What is the Circadian rhythm?
The circadian rhythm is the oscillation of protein and mRNA transcript levels in our body that follow an approximate 24-hour pattern. This rhythm is found in various tissues of our body (Figure 1). In our case we are interested in the circadian rhythm’s effect on metabolism, so we will look at the Food-Anticipatory Activity (FAA). The Food-Anticipatory Activity is when the oscillation of metabolism hormones (ghrelin, insulin, etc.) peak because the body anticipates food intake. This anticipation of food intake releases metabolic hormones that help to metabolize the food correctly and efficiently. Whether we eat at the wrong times or eat at the right times but our rhythm is off-sync, our body will not be prepared to metabolize the food correctly and as a result all the food would be stored away as fat, usually visceral fat (the fat in our stomach and around our organs).
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In a study [3] investigating the circadian rhythm of lipoproteinlipase [a protein enzyme that cleaves triglycerides into Free Fatty Acids and helps the uptake of Free Fatty Acids into adipose (fat) tissue] and obesity in nocturnal mice, it was found that when the mice were fed a high-fat diet during the day they gained significantly more weight than when fed during the night. This occurred because lipoproteinlipase oscillations did not peak during the day to properly metabolize fat. From this we can conclude that it is important to eat at the right times while our metabolism (lipoproteinlipase for example) is at its peak to correctly metabolize food (such as fat).
How does the circadian rhythm work?
The main circadian rhythm is maintained by the Suprachiasmatic Nucleus found in the hypothalamus. It can receive photic (light) inputs from the environment via melanopsin ganglionar cells. These cells signal the brain via the non-visual pathway through the retinohypothalamic tract to perceive whether it is day or night. Under natural conditions of sleeping when the sun sets and waking when the sun rises, our suprachiasmatic nucleus is reset correctly each day to tell our body whether it is day or night. Other organs and various tissues in our body also have a self-sustained circadian rhythm but receive input regularly from the suprachiasmatic nucleus so the whole body can be correctly synchronized together and with the external environment (see diagram below).
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Causes of Chronodisruption: (skip if you want to)
Now it is easy to see how modern society can promote disruption of the circadian rhythm. With the invention of televisions, computers and an increase in nightly leisure activities it is easy for individuals to stay up late at night staring into bright screens with enough photic signalling to cause our suprachiasmatic nucleus to perceive it is daytime. Consequently, when our suprachiasmatic nucleus sends the incorrect signal to our organs and peripheral tissues it forces their rhythm to change as well. The various rhythms in our body do not all change at the same rate and can take up to 7 days to re-synchronize. This means for an entire week our body is sub-optimal and unprepared to perform correct functions when required, such as the ability to metabolize food eaten at lunchtime because our body still thinks it is morning.
- Increase in nightly leisure activities that result in people sleeping later
- Followed by reduced sleep hours
- Frequent snacking throughout the day (and well into the night)
- Alternating meal times
How to Utilize the Circadian Rhythm to prevent Obesity:
Maintain an in-sync circadian rhythm by having regular timed exposes to Zeitgeber stimuli. This can be achieved by following a scheduled lifestyle that involves regular sleep-wake times, mealtimes, and exercise (the three main Zeitgeber stimuli). Here are some crucial steps to follow:
- Sleep at the same time every night (can be at any time as long as you are consistent)
- Sleep for 8 hours (give or take an hour) consistently
- Wake up at the same time each day
- Expose yourself (eyes in particular) to sunlight* during the day as much as you can
"But I like to sleep late on weekends"... THEN HAVE REGULAR MEAL TIMES!
You can maintain your metabolic circadian rhythm as long as you have regular meal times. Researchers found that animal models that had their suprachiasmatic nucleus removed (yes literally removed from the brain surgically) were still able to maintain their metabolic circadian rhythm by eating their meals at regular times. This indicates that the circadian rhythm for metabolism is independent from the suprachiasmatic nucleus’s rhythm (the main biological clock) and can be entrained by restricted feeding times. So even though you can't maintain a regular sleeping/waking cycles, it is important to eat meals at the same time each day (give or take 30 minutes) to ensure food is metabolized correctly and not deposited as visceral fat. However I must stress it is still important to sleep at the right time, to learn more about why read my article: "Preventing obesity with sleep"
The final advice is to exercise regularly for the same amount of time, at the same time each day to further entrain your body’s circadian rhythm. The best time to exercise is right before you eat because over time this scheduling will entrain your body’s circadian rhythm (and perhaps through classical conditioning) to prepare for food after every workout. In addition there has been research [2] that indicates the body is most effective at protein uptake right after a workout.
Chronoenhancement (Optional)
“Chronoenhancement” can maximize the body's efficiency to metabolize food and help to prevent fat accumulation. For those of you interested, chronoenhancement is the entrainment of our body’s circadian rhythm to become perfectly synchronized with the rhythm of the external environment (i.e. the sleep-wake cycle in-sync with the sunrise and sunset). Since we are biologically diurnal creatures (that are active in the day time), we can enhance our circadian rhythm by living as evolution has intended for us to live. How I try to enhance my rhythm in addition to the points I previously mentioned above is by:
1. Eating and completing all my work and errands during the daytime
2. Restrict eating to only three meals (and 3 small snacks if you desire) each day; I do
not eat at any other times
3. I do not look directly at any light sources (i.e. I stop using electronic devices with
bright screens) within an hour after the sunsets
4. I sleep within an hour after the sunsets
5. I sleep for 8 hours (give or take 1 hour)
6. I wake up early in the morning and try to expose myself to as much sunlight as I
can throughout the day
Conclusion: prevent chronodisruption by
- Maintaining regular sleep-wake cycles and to sleep for ~8 hours
- Eat at regular meal times
- Exercise regularly (preferably before your largest meal of the day)
- Eat at regular meal times
- Exercise regularly (preferably before your largest meal of the day)
Reference:
- Garaulet M, Ordovás JM, Madrid JA: The chronobiology, etiology and pathophysiology of obesity. Int J Obes (Lond). 2010 Jun 22. [Epub ahead of print]
- Weinert DJ: Nutrition and muscle protein synthesis: a descriptive review. J Can Chiropr Assoc. 2009 Aug. 53(3):186-93.
- Elmquist JK, Ahima RS, Elias CF, Flier JS, Saper CB: Leptin activates distinct projections from the dorsomedial and ventromedial hypothalamic nuclei. Proc Natl Acad Sci USA. 1998. 95:741–746.
For your Scientific Interest: Chronodisruption on health related issues other than obesity
Having an in-sync circadian rhythm is very important because not only will it help with obesity and metabolic function, but it will help to prevent many other associated diseases such as impaired glucose tolerance that can lead to diabetes, hypertension, dyslipidemia, endothelial dysfunction. Having an in-sync circadian rhythm will also help prevent against premature aging, and cancer and mental illnesses. The reasons why Chronodisruption can cause accelerated aging is because it causes cells to work when they don’t have to and work harder than normal. Chronodisruption can also lead to the development of certain types of cancer because when our body's rhythm goes out of sync the various systems in our body cannot effectively communicate and work well together; resulting in one system having uncontrolled malignant growth. Chronodisruption can also cause psychological illnesses because hormones and neurotransmitters are secreted in the brain at the wrong times resulting in mood disorders and emotional impairments. In a study with mice that had their sleep-wake cycle shifted 6 hours every week, it was found they experienced a significant reduction in life span. As well, they found that when (new) fetal suprachiasmatic nucleus (the main biological clock) were implanted into older animals, it helped restore the circadian rhythm and in effect they experienced increased longevity.
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