GNAWING on shreds of greasy meat, smearing barbecue sauce like tribal war paint, up to 31 competitors will vie on Friday at Wells Fargo Center for the 22nd annual Wing Bowl prize.

Surrounded by more than 20,000 drunken spectators and bevies of barely covered women, these warriors - including Eagle Jason Kelce - will continue Philly's tradition of gluttonous revelry.

But at what cost?

Missouri native Jamie "The Bear" McDonald returns to defend his title, having scarfed down 287 wings in 30 minutes last year. While he won $20,000 - money that he invested in equipment for his new barbecue restaurant in Connecticut - "The Bear" also consumed a gut-busting 14,350 calories of P.J. Whelihan's wings.

According to the USDA, active men ages 19 and older need about 2,500 calories per day to maintain a healthy body weight.

McDonald, a 37-year-old bodybuilder, ate about six days' worth of calories in a half-hour to earn that competitive eating crown.

Dr. David Metz, a Penn Medicine gastroenterologist, has conducted what he called "the most in-depth research on record" of the rarely studied, yet widely popular, activity. Observing how a competitive eater's brain ignored the stomach's signal to contract for digestion in the small intestine, Metz determined that a combination of "training and innate ability" separated speed eaters from the rest of society.

"A normal-size meal takes about four hours to digest," Metz said. "While food sits in the top half of our stomach during muscle relaxation, the bottom half grinds its contents with acid to squirt it into the small bowel. [Competitive eaters'] stomachs can expand to retain all of the food without increasing the acidic pressure, but it takes many days for them to release into the bowel."

Metz said that more intensive studying of a competitive eater, such as tracking an entire career, would be necessary to gauge the impact of body mass index and other variables.

"I can tell you they don't eat much between meals aside from high-calorie protein bars," Metz said. "And they exercise like crazy."

In addition to lifting and cardio, McDonald chews about 15 pieces of gum a day to prepare his jaw for the constant motion. Three to four days a week, he'll eat about five pounds of vegetables and drink lots of water to stretch his stomach.

"You have to stay in good shape to participate on a regular basis," said McDonald, who competes at least once a week in challenges across the country. "When you're coming down to the wire, like in the second round of the Wing Bowl, you have to push beyond your comfort zone."

Occasionally, McDonald worries about the long-term health effects associated with binge eating.

"Sometimes, I think about how expanding my stomach puts pressure on the other organs," McDonald said.

He has reason to worry, said Metz.

"If the stomach muscles repeatedly overstretch, the stomach may fail to contract. You could be liable for nausea, vomiting and tearing the lining of your esophagus. Plus, overeating makes you fat, and obesity is an epidemic in this country."