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The sleep – digestion connection

We know more about sleep, its benefits and the consequences of not getting enough sleep now, than at any point of time in human history. There are several organ systems and a multitude of functions taking place in the human body and it is concluded unequivocally that there is not a function or organ that does not benefit from a good night’s sleep. All these bodily functions, including sleep, takes place in a rhythmic fashion and the maintenance of these body rhythms determines the presence or absence of chronic health conditions.

Circadian rhythm is one among those and is controlled by our master body clock situated in the brain. It is a rhythm of great importance and controls our sleep-wake schedule. The result of this rhythm is sleepiness at night-time and alertness and wakefulness during daytime. The circadian rhythm also has an overarching effect on the human body and maintaining other bodily rhythms. Apart from one master body clock, different organs in our body also has organ clocks which determines the best time for each organ to carry out its function. For instance, the digestive system has its own organ clock, and a rhythm determined by it. It also maintains a bidirectional relationship with our sleep-wake pattern.

A cooler body temperature promotes sleep. You may have noticed that you slept poorly on a night when you ate late. Eating late at night affects our ability to fall asleep and maintain deep sleep. The digestive process leads to an increase in our core body temperature (temperature of internal organs) due to blood being rushed to the abdomen to aid in the digestive process and absorb nutrients. We sometimes tend to consider our digestive system as a boiler which should be able to function at any time of the day. But we forget that digestion is more effective at certain times of the day than other. Introducing food into your stomach closer to your bedtime is similar to you being called upon to do a few extra hours of work as you were getting ready for sleep and when you are least expecting it. So, avoiding food for 3 hrs before your bedtime will make it easier to fall asleep and maintain deep sleep.

Have you been trying to lose weight and not succeeding in it? It might be a good idea to look at your sleep patterns. Lack of sleep can lead to the imbalance of certain hormones that regulate your appetite and satiety. Ghrelin is the “hunger hormone” which is produced in our stomach, and it stimulates our brain for food intake. A sleep-deprived individual will have elevated ghrelin levels which will stimulate the person to eat more. On the other hand, Leptin is a “thinner hormone” and is produced in our fat cells. It signals to the brain that you had enough food. Unfortunately, sleep deprivation will lead to not having enough Leptin and you would not feel full until you eat more than you need. Often this can also mean consuming food closer to your bedtime and further disruption of sleep. The imbalance of Ghrelin and Leptin and the combination of two resulting processes, unfortunately, lead to overconsumption of food and result in weight gain.

The digestive process is also divided into different stages. The first stage occurs in the mouth where we produce saliva. The production of saliva begins with the thought of food and the introduction of food into the mouth. The saliva is rich in digestive enzymes and makes it easy for the stomach to further break the food down for digestion. The stomach also starts producing gastric acids at this stage. Saliva production also follows a certain rhythm with more saliva produced during the daytime than at night-time. Saliva also helps to neutralize the gastric acids if they came up through our food pipe. Eating late at night can result in gastric acids being produced in the stomach but not having enough saliva to neutralize it if they found their way up the food pipe. This can often trigger acid gas reflux and can be another sleep disruptor.

Having the right level of gastric juices facilitates proper digestion. Diminished gastric juices can lead to incomplete digestion of food and these undigested food particles can affect the health of the lining on the surface of the gut. Any damage to this lining is normally repaired with growth hormones that are produced during sleep. Insufficient sleep results in not having enough growth hormone for this repair work.

After the stomach phase of digestion, food passes from the stomach to the intestines where digestion driven by enzymes and chemicals continues. The movement of food in the intestine is done with the help of muscles that surround the intestine where it helps to squeeze the food further ahead. This squeezing of muscles also has a circadian component, where it is more active during the day and much slower at night. Eating a heavy male at night and retiring to bed immediately after eating, will slow the movement of food down the intestine and can also lead to acid reflux. Working with gravity and taking a walk or standing up helps to prevent it and increases your chances of getting better sleep.

The argument made above is based on science and concludes that sleep and digestion have a bidirectional relationship and when good habits are adopted it complements each other. Understanding your body clock of sleep and digestion, and altering our behaviours will help to obtain better sleep, ensure proper digestion, and maintain a healthy body weight.


Article by:

Motty Varghese

Sleep Physiologist

Delta Sleep & Sleep Therapy Clinic.


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