11/22/2012 03:57 am ET

Why Do We Eat Too Much On Thanksgiving And Always Have Room For Pie? (VIDEO)

Thanksgiving is a holiday centered around family, friends and of course, lots and lots of high-calorie food. And as the anecdote goes, no matter how much food is indulged, there's always room for pie.

The average stomach capacity is about 8 cups, according to The New York Times, but it can range from 4 to 12 cups.

A stretched stomach prompts the release of chemicals that tell the brain it’s full. But some holiday diners, faced with a sumptuous buffet of mashed potatoes and gravy, green bean casserole and pumpkin pie, keep eating.

As it turns out, there's a reason for that.

AsapSCIENCE breaks it down in a simple, but surprisingly comprehensive, video titled, "The Science of Appetite - Beating Overeating."

When the stomach is empty, it releases a hormone called ghrelin, which interacts with a neurotransmitter to turn on the desire to eat, thevideo explains. After eating, another hormone called leptin is released and turns off the desire to eat, making the body feel full.

So why doesn't this system work all the time?

AsapSCIENCE explains that in the past, energy rich foods with lots of fat and sugar were "hard to come by." Essential to survival, they became programmed as foods that were "extremely desirable." While it is now easy to get high calorie meals, the ancient desire remains.

Continual intake overrides the regulatory system of ghrelin and leptin, so that evolutionary quirk makes it hard for people to stop eating those types of meals, the video concludes.

According to the National Institutes of Health, obesity is a significant cause of morbidity and mortality worldwide. There has been a significant worsening of the obesity epidemic mainly due to alterations in dietary intake and energy expenditure.

As The New York Times points out, overeating during the holidays is not just a harmless indulgence, it can lead to indigestion, flatulence, the risk for heart attack, gallbladder pain and dangerous drowsiness when driving home.

However, everybody absorbs fats, sugars and other nutrients differently, the Wall Street Journal reports. Going for a walk after eating can help digestion, and exercising 12 or more hours before the meal can prevent a post-meal spike in a type of fat called triglycerides--one of the most damaging effects of a huge meal since it can contribute to the risk of having a heart attack or stroke.