Here's a snippet from a Time.com article about what happens to a person who competes in such a contest:
Not much research has been done about competitive eating. But several doctors from the University of Pennsylvania did an experiment for a National Geographic special, the results of which were published in the Journal of Roentgenology. They wanted to find out what happened to competitive eaters’ stomachs, so they compared two men: one champion eater and one non-competitive-eating man—the control—who simply had a “healthy appetite.”
The men were asked to consume as many hot dogs as they could in 12 minutes. The researchers noted that after eating the hot dogs, the competitive eater’s stomach “appeared as a massively distended, food-filled sac occupying most of the upper abdomen.” There was also “little or no gastric peristalsis,” the squeezing motion that normally helps the stomach break down food.
The article also talks about how competitive eaters basically trick their brain into letting their body ingest more. In other words, don't try this at home.