Postprandial Somnolence or Just a Food Coma?

Postprandial somnolence sounds like some sort of dreaded disease. But don’t worry.  Almost everyone has experienced postprandial somnolence at some time and lived through it without a scratch.

Don’t worry about family members catching it. Postprandial somnolence is merely the sluggish way people sometimes feel after they eat a meal; it’s sometimes humorously called going into a food coma.

Postprandial somnolence is made up of two elements:  sleepiness and low energy levels.  There have never been detailed scientific studies of postprandial somnolence, but most medical professionals have theories.

This article on postprandial somnolence will look at the various reasons people might experience it.

How the Nervous System Works

To understand this idea of postprandial somnolence, one needs to know more about the parasympathetic nervous system. The parasympathetic nervous system directs the activities of the entire digestive system, from making spit in the mouth, all the way to the end of the bowels.

Medical scientists think that the parasympathetic nervous system goes into this sleepy, resting phase after a meal because it senses the food in the stomach and bowels.  It is possibly true that the mere presence of food kicks off the sleepy response, but it is not proven.

Blood Flow Theory

Earlier theories thought that blood was pulled away from the brain and delivered to the digestive system causing people to feel sleepy.

Nowadays, the blood flow theory is not in favor.  Scientists have noticed that people can engage in strenuous exercise and not feel sleepy afterward.  Likewise, it makes sense that eating would not pull blood from the brain.  The body makes sure the brain has all the blood it needs, regardless of exercise or eating.

The Vagus Nerve

More scientists these days believe postprandial somnolence has more of a connection with a different nerve within the parasympathetic nervous system called the vagus nerve.

This nerve has attracted more attention these days because of a possible link to migraine headaches. In fact, with more studies, scientists have found that stimulation of the vagus nerve can affect how much pain is felt during a migraine.

On the other hand, during digestion, the vagus nerve is very busy.  When the vagus nerve is activated by food in the digestive system, it makes the body release several hormones.

One of the hormones released is melatonin.  Most people today are familiar with melatonin as a sleep aid, so clearly this is something that is contributing to postprandial somnolence.

Rising and Falling Glucose Levels

Something else that might contribute to sleepiness after meals are the increase in sugar in the blood.  Too much blood sugar can make people feel sleepy until the body releases enough insulin to regulate the glucose.

When a person eats, their glucose level goes up, the body starts putting out insulin, and the glucose eventually drops. These swings in blood glucose often make the body feel fatigued and sleepy.

When people say they feel tired because they had a heavy meal, this refers to having a lot of foods that are heavy in carbs and sugars and make the stomach feel full.

The Food Itself

Then there is the allergy theory.  Many people don’t realize they have a food allergy or a food intolerance.  In many cases, a sensitivity to certain food can make people feel fatigued after a meal containing those particular foods.

Here’s where the migraine/vagus nerve connection comes into play.  If a person does indeed have an undiagnosed food sensitivity, that person might wake up with a migraine in the morning after eating the offending food.

These people may have had the postprandial somnolence the night before after they ate, then the next morning the stimulation of the vagus nerve from a food intolerance brought on the morning migraine.

The Size of the Meal

Reading all these reasons for a food coma, most people would wonder why postprandial somnolence doesn’t happen after they eat a snack or a small bowl of soup.  Why does it only happen after a full meal?  Why are the symptoms worse after eating too much?

When people eat, the stomach stretches to accommodate the food.  This stretching action stimulates those pesky nerves in the parasympathetic nervous system mentioned earlier and they cause the body to produce more of those hormones.

More questions come to mind.  Why doesn’t drinking liquids make a person sleepy?  Why is it only solid foods that cause postprandial somnolence?  This is explained by the different sections in the human stomach.

Studies show that liquids are processed in the fundus, which is the upper part of the stomach.  Solids are processed in the antrum, which is the lower part of the stomach.  Obviously, the two different stomach sections have different connections to the brain.   The bottom section sends more of the sleepy signals.

It’s Not Turkey

As scientists and doctors examine the various theories about what causes postprandial somnolence, they have discovered a few things that do not cause postprandial somnolence.

For years and years, people have thought that the reason they fall asleep after Thanksgiving dinner is that turkey has tryptophan.  Well, guess what?  Beef and pork and chicken also contain tryptophan just as turkey does.   Oatmeal has tryptophan and so does milk.

Tryptophan is an essential amino acid that your body can’t make on its own. It has to come from plants and animals that we eat.  But the relationship between tryptophan and sleepiness is not direct.

Digesting the food in your stomach makes your blood sugar rise.  Rising blood sugar triggers your body to release insulin.  Insulin triggers your body to sweep out all the other amino acids, except for tryptophan.  The tryptophan is then converted to serotonin in the brain.  Serotonin is what is believed to cause sleepiness and contributes to food coma.

Thanksgiving dinner probably makes people more sleepy because they eat too much food, drink alcohol, or eat too many carbs.  Time to stop blaming the poor turkey.