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​Circadian Clock: The Link between Sleep and Digestion

Posted by Deborah Graefer, L.Ac., MTOM on

Have you noticed how you feel so sleepy and lethargic after a big meal? Or how you can’t sleep when you’re hungry? Or how your digestive issues seem to be worse after a bad night of sleep? Not to mention the fact that gastrointestinal symptoms make sleep elusive. You have probably experienced at least one of these but just can’t put your finger on how it is that gut affects your sleep and vice versa.

The common denominator between sleep and the digestive function is the circadian clock. Some also simply call it our body’s clock. The circadian clock is a complex mechanism that synchronizes our endogenous systems with the 24-hour day. It helps control a wide variety of biological processes, the most popular of which is the sleep and wake cycle. Other functions regulated by the circadian clock are hormone secretion, body temperature, intestinal function, metabolism, glucose balance, and immune function. And if you’ll notice, most of these biological functions have something to do with digestion and sleep.

changing work shiftsUnfortunately, despite the importance of maintaining the circadian clock, many of us engage in activities or a lifestyle that causes its disruption such as:

  • jetlag
  • excessive exposure to technology and artificial lighting
  • round-the-clock access to energy-dense foods or power 

Disruption of the circadian rhythm adversely affects the body’s functions including our ability to breakdown food or sleep soundly. It influences and affects the regulation of up to 30% of genes expressed in tissues including the liver and the gut. Incidentally, our digestion and sleep patterns can also dictate the shift of the circadian clock. Misalignment of the body’s natural rhythms based on the daily behavioural patterns of people is detrimental to cells, tissue, and whole-organism function.

How does sleep affect digestion?

Before anything else, let’s qualify what is considered a good quality sleep. Technically speaking and as defined by the National Sleep Foundation (NSF), we have had a good quality sleep when:

  • We have slept at least 85% of the total time we spent in bed.
  • We fell asleep within 30 mins or less.
  • We woke up no more than once during the night.
  • We didn’t stay awake for more than 20 mins after initially falling asleep.
  • We wake up feeling recharged and refreshed.
  • We feel fully alert and productive throughout the waking hours.

Also, NSF states that adults should optimally receive between 7-9 hours of sleep during night time, although some may be fine with 6-7 hours at night with a short daytime nap.

1.Lack of good sleep can cause gastrointestinal problems.

The circadian clock can directly control cellular respiration and other cell-powering functions, especially in frequently-dividing cells such as the epithelial cells of the gastrointestinal tract. Immune homeostasis, microbial balance, and gut permeability are also governed by the clock. This allows for the coordination of digestive system physiology with the environment. Therefore, if the circadian rhythm is disturbed via the lack of good quality sleep, it may cause the development and progression of diseases both inside the gut and out.

A lot of changes also happen to the gut while we sleep. Gastric emptying is slower during sleep although the pace picks up bit during the rapid eye movement phase (REM). During the night, we also have a more regular intestinal motility than during the day. The colon also has decreased muscle tone and contractions while the anal canal has lower pressure. Sleep is critical to give the digestive system time to rest and recover. Studies actually suggest that getting a good quality sleep and maintaining the body clock is critical to achieving homeostasis in the gut/liver axis as well as keeping the intestinal barrier integrity. Leaky gut, IBS, peptic ulcer, and GERD are common among those who do not have normal and consistent sleep/wake cycles or regular meal times.

2.Lack of good sleep contributes to erratic metabolism.

Metabolism is also governed by the circadian clock. Nocturnin, a gene which is an output of the body clock, affects metabolism by modulating the stability and translatability of messenger RNAs. It affects lipid metabolism and mitochondrial functions outside the intestine. In other words, the circadian rhythm controls metabolism by modulating the expression of metabolism-related genes.

Lack of good quality sleep and the continuous disruption of the circadian clock increase the risk of developing metabolic syndromes and non-alcoholic fatty liver disease (NAFLD).

3.Lack of good sleep affects the liver and gallbladder

Speaking of NAFLD, lack of good quality sleep is bad news for the liver, gallbladder, pancreas, and other metabolic tissues. Normal circadian rhythms which entail regular and consistent sleeping and eating times, is crucial in bile acid metabolism. Bile acid signalling affects metabolic balance by regulating insulin secretion from the pancreas. Bile acid synthesis is also connected to the body clock via the regulation of specific genes and proteins. In addition, it regulates the cholic acid synthesis enzyme and other key enzymes in bile acid synthesis.

Bad eating and sleeping habits can influence fatty acid synthesis and contribute to abnormal bile acids and liver damage. These habits also encourage a pro-inflammatory state that can lead to more problems not just within the digestive and biliary system but systemically (within the whole body).

4.Lack of good sleep leads to stress.

We all know that we feel stressed and irritable when we don’t get enough rest. But do we know why exactly? Aside from the fact that sleep gives the mind a time to rest and recharge, studies also support the theory that cerebral free-radicals accumulated during productive hours of the day are removed during sleep. As we sleep at night, the formation of free radicals is slowed down significantly and our natural antioxidant mechanisms are increased.

When we don’t get enough sleep, the pituitary gland-dependent hormones are also altered. The level of our stress hormone cortisol shoots up. Frequent sleep deprivation also puts the body on survival mode, wiring up the nervous system towards the adrenaline response. Long term operation under the survival mode also influences cortisol and may promote the development of insulin resistance, inflammation, high blood pressure, depression and other health conditions. It also simply makes us irritable, less productive, and less focused during the day.

5.Lack of good sleep contributes to obesity, weight gain, and insatiable appetite.

Sleeping and eating are very closely interwoven. Hormones that regulate appetite and satiety are severely affected by sleep deprivation. Leptin, a hormone released by fat cells, send satiety signals to the brain which suppresses our appetite. And when we don’t get enough sleep, the plasma concentration of leptin is significantly decreased, particularly at night time. And concurrently, ghrelin, a peptide secreted by the stomach which stimulates appetite, is stimulated during sleep loss. These hormonal fluctuations alter the body’s ability to tell when it’s time to eat and when it’s time to stop. This easily leads to excessive caloric intake.


How the Gut Influences Sleep

While sleep can influence gut health and digestion, the opposite can also be true. What, when, and how we eat can influence the quality of our sleep and eventually shift the circadian clock. I experienced this myself when I made the leap to cut out all sugars, grains and nightshades – all common inflammatory foods. My sleep improved immensely!

In animal experiments, the compositions of foods have been shown to influence the circadian rhythm. High protein, low carbohydrate foods supported regular body clock function as tested from the genes in kidneys and livers of mice. In human trials, switching participants from high carbohydrate/low fat diet to low carbohydrate/high fat diet, delayed and increased the amplitude of cortisol rhythms. It also influenced metabolic gene expression and changed the body’s inflammatory response. Folate, magnesium and zinc deficiencies have been linked with lower melatonin levels in rodents and in one rodent study, vitamin B6, either alone or in combination with zinc, increased plasma melatonin. Melatonin is the hormone that stimulates sleep.

A 2007 research by the National Health and Nutrition Examination Survey (NHANES) involving 4,548 people showed that people under different sleep categories have distinct diet patterns too. Short sleepers consumed the most calories while long sleepers consumed the least calories. Very short sleepers drank less water and consumed fewer total carbohydrates and lycopene. Short sleepers tended to consume less vitamin C, water and selenium (found inspinach, halibut, sardines,etc.), but more lutein or zeaxanthin (found in green leafy vegetables). Long sleep was also associated with consuming less theobromine (found in chocolate, cocoa, and the likes) and drinking more alcohol. Lastly, normal sleepers showed the highest food variety in their diets. A varied diet tends to be a marker for good health since it includes multiple sources of nutrients.

There are certain foods and drinks that can obviously alter our sleeping patterns such as those with high levels of caffeine and alcohol. But aside from that, sugar affects sleep too. Heavy foods that are spicy and fatty are also more difficult to digest which can affect the quality of our sleep. Even our level of hydration can also determine whether we can achieve a deep, restorative sleep or not.

How to Achieve Both Restful Sleep and Healthy Gut

Now that we know the link between sleep and digestion, it is important to follow 4 simple rules that may help achieve both a restful sleep and a healthy gut.

1.Do not overeat.

This is always rule #1 no matter what physical condition you are in. Moderation is key.

2.Maintain a healthy diet.

If you are still confused as to what a “healthy diet” means, feel free to use our grocery food list available from our gallbladder diet page. That is always a great starting point when you want to make better food choices.

3.Mind the timing.

Remember the saying, “take breakfast like a king and supper like a pauper”? That’s true. For better digestive function and optimum rest at night, mind the frequency, timing, and even duration of your eating.

4.Remember your table manners.

When we think about it, table manners do not just look good, they serve a purpose. I am not talking about the right direction to pass food or proper way to fold the napkin. It’s the more practical ones like, we don’t talk when our mouths are full because we should focus and take time to masticate our food. We also shouldn’t eat while watching TV or working as this increases cortisol and lowers secretion of digestive juices. Using cutlery can also be helpful so we can mind the portion, servings, and the duration of eating. This is contrary to eating from fast food take away boxes and packets where it’s easier to take larger bites and you really can’t visually judge whether you have had enough or not.


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