Picture this: It's April 16, and nearly 24,000 qualified participants of the 111th Boston Marathon are anxiously awaiting the starting gun.

Within the field, though, are a dozen people — weighing 250 to 525 pounds — who will disregard the norm and walk an abbreviated stint of the 26.2-mile race.

"For the first time in history," said Julie Laughlin, with a smile, "they allowed people who didn't qualify."

The race was just the first leg of the new ABC reality show, "Fat March," which challenges its 12 obese contestants to shed pounds by walking from Boston to Washington, D.C.

And on Tuesday afternoon, the cast and crew rolled into Lancaster city — Central Market, in fact — for one of the show's eight challenges, which periodically break up the 500-mile journey and provide opportunities for contestants to bank incentives.

Working in groups of two, contestants Tuesday had to fill baskets with a shopping list of food items that could be found at various stands in the cavernous market.

Given that the challenges offer "great prizes," as executive producer Laughlin put it — although she wouldn't reveal what Tuesday's prize would be — the market air swiftly grew competitive as contestants rushed around to collect specific products from the food stands.

"They're not staying together! They're not staying together!" complained Michael, one of the contestants, while pointing out the culprit pair to the cameras.

"I was told portions didn't matter," said contestant Jamilyn in disgust. "And now, if we don't have enough we're going to have to start over."

"We were here before, and you said you didn't have any!" yelled contestant Chantal to a salesman, who gave another contestant a product she thought was sold out.

And on and on it went.

Amy Eschelman, saleswoman for Barr's Farm, said market workers were warned of the impending reality show taping Saturday. She admitted she had "been waiting all day" for the contestants to arrive.

And about 3:20 p.m., they finally did.

During the ensuing 30 minutes, "Fat March" cast and crew flooded the market, which remained open for determined contestants rushing around the market floor as well as customers willing to brave the countless cameras.

Eschelman said contestants approached her stand at one point during the madness, demanding to buy specific types of fruits, including her baby bananas, champagne mangoes, blueberries and raspberries.

"One of the contestants even told me not to give another contestant some fruit," said Eschelman, laughing. "But I gave it anyway."

In an interview after filming ceased for the day, Laughlin said the purpose of the show is to dispel the belief that obese people can lose weight only by undergoing intense workouts at the gym.

Instead, she said the show, tentatively premiering in August, aims to teach viewers that proper dieting and simply walking — albeit 500 miles — will dramatically reduce a person's waistline.

Reality shows like "Fat March" wouldn't even exist if it weren't for America's obesity problem, which co-host and trainer Lorrie Henry dubbed "huge."

"No pun intended," Laughlin chimed in.

Henry cited the percentage of obese Americans — now at 64 percent — as one reason she applied to be a trainer on the show. She also said she used to be overweight herself and immediately wanted to jump on board to "change people's lives."

"My experience on the show has been amazing; overwhelming," said Henry, a resident of Phoenix. "I've seen amazing things."

Co-host and trainer Steve Pfiester said he was attracted to the show's "positive spin."

Instead of contestants getting voted off each week, all 12 can ultimately reach the finish line in Washington, D.C. — and share the $1.2 million grand prize — as long as they walk the required mileage and don't hold back the rest of the group.

"These people are walking 12, 15 miles at a time," Pfiester said. "They're learning to overcome obstacles."

E-mail: ehughes@lnpnews.com