Pastor Joe Wilcots knew it was time to lose weight when he glanced at a photo of himself at a church function and thought: “Who is that fat little man?”

He’d already noticed some members of his flock, at Disciples of Christ church about an hour from Jackson, Mississippi, were unhealthily heavy; one man weighed nearly 450 pounds. And that was hard to see. “As a pastor when you look out over the congregation and see people overweight, then you want to help them,” said Wilcots.

So when his neighbors – a reverend and a doctor – asked Wilcots about introducing a weight-loss program to his church, he felt it was “going to be good for the body of Christ”.

For four months, every week after Friday evening service, Wilcots turned his pulpit over to Dr Erica Thompson, a Jackson-based practitioner specializing in community health. The entire congregation took part. The first thing Thompson told them was that, based on state statistics, one in three people in the room was at risk of developing diabetes. The second thing she told them was that losing just a few pounds, 5% to 7% of their body mass, could prevent that from happening.

The curriculum covered everything from emotional eating to sugar substitutes to exercises that could be done in front of the TV, all geared towards small adjustments rather than drastic life changes. The 21 men and women who took part in the program were weighed each week, and by the end, they’d lost a total of 132 pounds.

That might not seem like a lot, but research has shown that moderate weight loss and exercise is even more effective than drugs when it comes to preventing someone from developing diabetes. It seems simple, but doctors have been telling patients to lose weight for years, and diabetes rates continue to climb.

What Thompson and other healthcare professionals have come to understand is that the weight loss imperative matters a lot more to most people when it comes from someone they know and trust. Often, that person isn’t a doctor. It’s an idea that has taken root even at the highest policy level: the Centers for Disease Control (CDC) diabetes strategy includes efforts to train congregation nurses and community health workers. But putting it into practice has been challenging in a health insurance climate that still favours treatment over prevention.

Mississippi has the second-highest rate of type 2 diabetes in the country. Nearly a quarter of a million people in the state, or 12.5% of the population, have been diagnosed (the national average is just under 10% of the population).

When diabetes is not managed correctly, which is often the case in low-income, under-insured and geographically isolated places like rural Mississippi, the disease quickly leads to a host of other problems: nerve damage, heart disease and blindness. The total cost of treating diabetes, and complications caused by it, is $245bn per year in the US.

Thompson first began to understand the devastating effects of diabetes when she graduated from medical school and got hired at an amputation prevention clinic in Jackson. Her patients were people who were already feeling the ravages of the disease, including one woman who’d lost one leg below her hip and was in danger of losing the other. The woman died not long after Thompson met her, but she left a strong impression. “I thought it would be so great if we could think of a way to do prevention rather than treatment,” said Thompson.

In 2009, after funding for the amputation clinic ran out, Thompson and her husband started a nonprofit, Magnolia Medical Foundation, to try to do just this. The first program they ran, at a church in their hometown of Natchez, was very well received. In her clinical practice, Thompson said, she often senses that patients feel compelled to say the right thing even if they’re not doing the right thing, which makes treating them more difficult. But in that first church in Natchez, she right away saw that people were more open. They were more likely to bring up problems, or admit to struggling – which meant she could offer guidance. In church, Thompson said, “we’re in your world. And we want you to be yourself. There’s no judgment about it.”

Martha Moss, an ebullient 54-year-old star singer in the church choir, lost 11 pounds in the program at Disciples of Christ, which started in January this year. Moss said her doctor has told her plenty of times to lose weight, and that over the years she tried and failed on a number of commercial programs, including Weight Watchers. But Thompson’s approach brought up things she hadn’t thought about or seriously considered before: the kinds of emotional triggers that can bring on binge-eating, for instance, or the amount of sugar that common treats actually contain.

“I know that Coke wasn’t good for you, we’ve all heard that,” Moss said. “I never knew it was so much sugar in Coke. I was just shocked.” The changes that she’s made have been small, said Moss, but profound. “I think we were at a point where we really kind of needed it,” she said. “To be beneficial to the Lord, as far as being able to witness, you’ve got to be in good shape.”

This kind of religious rationale for weight loss may seem awkward to a secular audience. But, as Thompson pointed out, the very communities with the highest prevalence of diabetes – African Americans and Hispanics – are also the demographics that are likeliest to attend church.

Dr Richard Pratley is the director of education and research at the Florida Hospital Diabetes Institute, and is focused on preventing and treating diabetes in the historically black community of Eatonville, Florida, where 25% of the population has already been diagnosed with diabetes. When he heard about Thompson’s work, he reached out for advice on how to frame the program in spiritual terms to get pastors on board. This kind of approach is slow, he says, because it’s got to come from within – not from doctors like him. “Any time you are working in a community, you have to build trust with a community. It takes time,” he said. “There’s no quick fix.”

And, because it’s out of the traditional healthcare realm, the question of how to pay for this type of program is complicated. The CDC’s Diabetes Prevention and Control Program, a federally funded and state-based program, identified recruitment and training of people in community and faith-based organizations as a key priority. But the CDC doesn’t cover the cost of actually running the scheme, which is between $300 and $450 per person. Thompson funded her work at the Disciples of Christ church through a grant from the state health department, and Pratley provided his program through various foundation grants and individual donors. Both kept them free for participants.

Dietrich Taylor, director of the state’s diabetes prevention program, said he is working to get state departments to offer the program to their employees at work through insurance. Thompson said she’s had informal talks with insurance companies that are interested in covering the program as well on performance-based measures.

“Because, why do we have to wait until you have it?” asked Thompson. “We spend so much more to treat as opposed to sit down with someone. It’s reactive instead of proactive, and it’s always cheaper on the other side.”