Oh, come on. It happened to you last Thanksgiving, right? You know exactly how it feels; you shovel down a huge meal and despite the promise of an exciting ballgame, you fall asleep for several hours and wake up after the sun's gone down. Well, it happens to some dogs, as well. They shovel down a meal, and despite the promise of an exciting ballgame (chase, not football), they fall asleep. It even happens to animals other than dogs. In the summer of 2015, a bear estimated to weigh as much as 500 pounds broke into a Florida homeowner's garage, tore open a 20-pound bag of dry dog food, ate his fill, and promptly fell asleep. The bear even slept for another half-hour after the owner returned home!
The Root of the Behavior
Call it whatever you want; the after-dinner droop, food coma, or even "the itis," the post-supper snooze is an understood medical phenomenon called "postprandial somnolence." So it has a name, but very little actual medical research has been done on it. That said, scientists do have a number of theories regarding why it happens. One theory holds that when a dog (or human) begins to eat, his body begins to rev up the parasympathetic nervous system (which governs digestion and a number of other automatic body processes) and to slow down the sympathetic nervous system (which generally governs the 'fight-or-flight' response).
Another theory is that when a dog (or human) eats, their insulin level increases. This is a known biological mechanism. However, insulin enhances the body's absorption of several different amino acids, but not tryptophan. This is important because tryptophan is chemically converted into serotonin in the brain, which is then converted into melatonin. Both serotonin and melatonin are known to have sleep-inducing effects in humans and dogs, and melatonin tablets are sold over-the-counter as a sleep aid in many pharmacies and health food stores.
There are other, more complex theories; two involve rather complicated biological processes that impact how potassium is used in the body. Again, very little actual biological or chemical research has been done on these theories. Primarily, these theories were developed by scientists using already-known and well-studied mechanisms to arrive at reasonable and possible explanations for why dogs (and humans) get snoozy after a meal.
Speaking of being snoozy after a meal, have you heard of a Great Pyrenees puppy named Jack Damn It? Jack Damn It, or Jack, lives with his owner in North Carolina. One day in the fall of 2017, Jack's owner came home to find Jack asleep - in his food bin, which was completely empty, as Jack had wolfed down everything inside before being caught by "the itis." Jack enjoyed a brief period of fame on Reddit for his deed.
Encouraging the Behavior
While napping after a meal isn't unusual, it is possible for it to become excessive. And there are some legitimate veterinary reasons why your dog might be exhibiting unusual fatigue. One hazardous issue arises when a dog's circulatory system and liver don't work together properly, leading to an increased level of ammonia in the bloodstream as the liver doesn't sufficiently extract wastes from the blood. The problem is called a "portosystemic shunt," and it can either be present from birth or develop over a dog's lifetime. The abnormal connection between the two can cause a condition called hepatic encephalopathy - and a major symptom of that is excessive drowsiness. If your dog is always or nearly always sleepy, consider asking your vet about this condition. Blood panels, X-rays, and a fasting bile acid test can help reveal the issue if this is actually the cause. It is also possible that a dog that's often sleepy could be suffering from chronically low blood sugar levels. If you suspect this could be the case, ask your vet. If this is the cause of the problem, then you might be able to remedy it with a change in diet. If your dog's blood sugar levels are dropping significantly after eating (this is due to the body releasing insulin), you might find that a diet with fewer carbohydrates helps. Blood sugar is known to drop more after higher-carb meals than after meals with lower carb levels.
Other Solutions and Considerations
There are a number of claims and folk wisdom nuggets surrounding the post-meal droops; since it is more-or-less a universal biological phenomenon (at least among mammals), people have been speculating about the cause for ages. One of the more common claims is that after a meal, the body directs more and more blood to the gastrointestinal system and less and less to the brain. Since the brain's blood flow is reduced, the thinking goes, so too is its oxygen supply. And with less oxygen available, the claim is that sleepiness results. This is known to not be true, as the body strictly controls and maintains blood flow to the brain; it doesn't drop after a meal. Another false theory is weirdly specific. In this theory, the overwhelming desire to nap after a large Thanksgiving or Christmas meal is due to the fact that turkey - the traditional entree - is extremely high in tryptophan. The only problem with the theory is that turkey contains no more tryptophan, on average than any other meat, including beef and ham.
Regardless of the cause, sooner or later your dog will succumb to after-dinner drowsiness. While there are some possible medical issues relating to general fatigue, so long as your dog isn't demonstrating unusual fatigue that just won't go away and which doesn't seem to be related to meals, chances are good that there's no cause for alarm. Provide a clean, soft bed, a satisfying meal and plenty of water, and get out of the way.