After a large meal (a Thanksgiving feast can easily exceed 4,000 calories), cardiac output of blood is increased and diverted to the intestinal circulation to aid digestion, which can take as long as 6 hours, leaving other organs, including the heart and brain, relatively deprived. The work involved in all this shunting around of blood might be the equivalent of vigorous sex or moderate exercise.
But that's not all. An increase in insulin, triggered by the carbohydrate content of the meal, can compound the situation by preventing normal relaxation of the coronary arteries.
Triglyceride elevation, from the fats and carbs, can impair the function of the inner lining of the coronary arteries and cause those vessels to become less elastic and acutely inflamed. Increases in inflammatory markers such as C-reactive protein have been noted following a large, high-fat meal. And the rise in blood pressure that usually occurs after eating such a meal can cause those inflamed patches to rupture, which in turn can lead to blockages and heart attacks.
Gobbling down a huge dinner can have other health consequences, too. The prodigious amounts of gastric acid produced during the body's effort to digest the food can cause acid reflux that often goes on for many hours. The high fat content of a typical holiday feast can precipitate a gallbladder attack in people who have gallstones. The high salt content might trigger acute heart failure in someone with a history of that condition.
Add to those possibilities the sleepiness generated not only by the meal but also by the wine one might imbibe (making the drive home an accident waiting to happen), waking up the next morning with acute gout, plus the embarrassing flatulence, and you have many good reasons to revamp your eating habits at Aunt Fannie's fabulous feast this year.
The only thing you probably don't have to worry about is rupturing your stomach. That rarely happens because it can expand to accommodate nearly four times the normal volume of food.