Do you know that the process of digestion takes more vital energy than any other bodily process? Even exercise! When we eat one or two food groups at a time, say protein and vegetables, the body can easily break down those foods, separate the vitamins and nutrients it needs from the waste it doesn't need, and leave you feeling energized to do other things. But give it a meal like that crazy holiday ensemble and it pretty much has to shut down business for any other bodily activities until it can attend to that mess in your gut. And, I do mean mess!
Because at this point, the meal is not providing you any nutritional value. It's only providing a mess to be broken down and discarded. It's kinda like when you drop a jar of peanut butter in the grocery store - Clean up on aisle six! How can you get any value out of food that's lying spilled on the floor?