The world's biggest appetites will duke it out for the title of Nathan's Famous hot dog eating champion this holiday weekend. And if all goes according to plan, the winner will scarf down more than 68 wieners -- breaking title holder Joey "Jaws" Chestnut's record -- in 10 minutes flat.

The contest is the crown jewel of the competitive eating circuit, a string of events that involve inhaling everything from cheesecake (11 pounds in nine minutes) to jalapenos (275 in eight minutes). To gear up for the showdown, competitors prime their stomachs by chugging gallons of water or milk and consuming giant amounts of food. "It's similar to training for a marathon," Chestnut has said.

Of course, no one can confuse this practice with healthy competition. Eaters take in more than a week's worth of calories -- roughly 16,000 -- in mere minutes. But what kind of toll do these feats take on the body over the long run? And how do these men and women fit in all that food, anyway?

The fullness factor

To get the goods on these questions, doctors from University of Pennsylvania's Perelman School of Medicine studied competitive eater Tim Janus in action. They watched as he polished off 36 hot dogs in 10 minutes without getting full. To put that in context: An ordinary guy managed to eat only seven before feeling sick. Their X-rays revealed that Janus' stomach took longer than usual to start contracting and moving food into the digestive tract.

"Speed eaters have very compliant stomachs," said David Metz, M.D., a gastroenterologist who was one of the study researchers. Usually, the expanding stomach fires off a message through the vagus nerve to the brain, which then relays the sensation of fullness. "But these people somehow block that signal, so they don't experience the feeling of increased tension until much later," he said.

Metz suspects that stretching the stomach -- as Chestnut does with his training regimen -- may teach it to tolerate enormous quantities of food. "Part of it may be genetic, as well," he said. Some folks may have iron-clad guts that give them an edge, just as Michael Phelps' extra-long limbs give him a leg up against other swimmers.

Risky business

Other than choking on a frankfurter, the most obvious occupational hazard for competitors is weight gain. But take a look at the Nathan's Famous lineup, and you'll see that most of the favorites cut pretty slim figures. Sonya "Black Widow" Thomas, for instance, weighs in at just over 100 pounds.

According to these eaters, maintaining a healthy weight actually helps their cause. The theory is that belly fat may block the stomach from ballooning to its maximum size during contests. That's why many keep their calories in check, training by consuming veggies and working out regularly. Chestnut and others also stick to a liquid diet in the days leading up to and following a contest.

Another potential risk is that the stomach may not bounce back, according to Metz. Eventually, it may lose its ability to contract and empty properly, causing chronic indigestion and nausea. The bottom line is simple: Don't try this at home! Stick to a couple of dogs at the BBQ and leave the inhalation -- and stomach aches -- to the pros.