Fruit and vegetable prescriptions provide money for low-income families to shop with at farmers markets. (Ceiling and Visibility Unlimited)

Every Wednesday, as many as 45 people, ages 12 to 70, meet at the Unity Health Care Upper Cardozo clinic for the weekly meeting of We Can. The program welcomes low-income families that struggle with obesity or chronic disease. On some nights, there are cooking classes; on others, participants do yoga. Every week, they receive plenty of information about how to develop a more healthful lifestyle by shopping smarter, exercising and eating more fruits and vegetables.

It’s great advice — in theory. But when it comes to buying fresh produce, needy families often find the advice difficult to follow. The familiar refrain: Fresh fruits and vegetables can be expensive and scarcely available in poor neighborhoods. “We have a motivated group of people who want to make changes,” says Jessica Wallace, We Can’s coordinator. “But financially, they are at a loss for how to do that.”

Wallace has a new way to help. On June 6, the clinic began writing “fruit and vegetable prescriptions” to help cover the cost of fresh produce. Thirty-five families will receive vouchers for $1 per family member per day — $112 every four weeks for a family of four — to spend at any of five District farmers markets: the Columbia Heights Community Marketplace, Mount Pleasant, 14th and U, Bloomingdale and Glover Park. The hope is that a medical endorsement of healthful eating, plus cash to buy ingredients, will help families make real changes to the way they shop and eat.

In the fight against obesity, many solutions are more stick than carrot: taxes on sodas, bans of junk food in schools and, most recently, New York Mayor Michael Bloomberg’s proposal to ban the sale of sugary drinks in servings larger than 16 ounces.

The produce prescription program, in contrast, is the brainchild of Wholesome Wave, a nonprofit organization that specializes in incentive programs to encourage healthful eating and lure new dollars to farmers markets. (Its hallmark initiative is its Double Value Coupon program, which doubles the value of food assistance benefits, such as food stamps and WIC, if shoppers spend their money at farmers markets.)

The District is the latest to launch produce prescriptions. The program, now in its third year, already has shown remarkable results: Of the 1,200 participants in six towns and cities in the Northeast, 66 percent said they ate more fruits and vegetables as a result of the program and 38 percent improved their body mass index, a standard measure used to estimate healthy body weight. The program brought new customers to farmers markets. More than half of families that received fruit-and-vegetable prescriptions had never, or rarely, been to a farmers market.

“Our goal is nothing less than to prove that eating more fruits and vegetables makes people more healthy,” says Michel Nischan, Wholesome Wave’s founder and chief executive. “We want to show that by funding these programs, we can help reduce what we spend on health care.”

Prescribing food as a cure dates at least to ancient Greece, where the physician Hippocrates counseled: Let food be thy medicine. In the 1960s, Jack Geiger, a doctor in the Mississippi Delta, persuaded local grocery stores to fill prescriptions for food for his malnourished patients. But over the past half-century, the connection between diet and health has been overshadowed by the health-care industry’s high-tech, and reimbursable, treatments.

“We talk a lot about health in a holistic sense, but we haven’t been empowered to endorse it in any way,” says Shikha Anand, a doctor in Boston who helped develop the prescription program. “I could write prescriptions all day long for amoxicillin. But I couldn’t prescribe a tomato.”

When it comes to health care, American society likes its medicine to come with a guarantee: “clinically tested,” “doctor-approved,” and so on. The focus on treatment, rather than prevention, stems from the fact that it’s not easy to pinpoint good nutrition’s impact on health. But Anand was keen on the fruit-and-vegetable prescription program collecting data to prove its worth. Patients report their consumption of fruits and vegetables. Doctors regularly record the subjects’ weight and blood pressure. The program tracks patient visits to health-care clinics (71 percent of patients return more often to clinical obesity programs) and farmers markets (51 percent of patients visited the farmers market eight or more times).

The results are winning over physicians. Michael Lambke implemented the program in the poor, rural community of Skowhegan, Maine. In 2011, 76 percent of patient families attended sessions at the clinic at least three times and made 10 trips to the farmers market, spending more than $5,000 on fresh produce.

Anecdotally, the program is inspiring families to embrace other aspects of a healthful lifestyle, Lambke says. One family got friends to join the program. Another tried out a new walking trail. “The best quote was a kid who came back to me and said that the thing he liked about the program was that his parents played with him more,” Lambke says. “Oh, man. That was awesome.”

In the District, three groups are working together to implement the fruit-and-vegetable prescription program: Unity Health Care is distributing the prescriptions. The Columbia Heights Community Marketplace and DC Greens, a nonprofit organization that runs incentive programs at area farmers markets, are handling tracking and redemption. On the first Saturday of the program, 26 patient families filled their prescriptions, spending $708 at the Columbia Heights market.

The program is starting small; it will distribute just $26,000 in vouchers during the 24-week farmers-market season. But it hopes to expand to new clinics and new markets in 2013. New funding could come from Wholesome Wave or the D.C. City Council, which is supporting farmers market incentive programs for those who receive food stamps and WIC. In 2013, the District’s Department of Health will allocate $50,000 for these programs.

But it might not take a lot of money, at least in relative terms, to make fruit-and-vegetable prescriptions work.

“They come back once a month. It’s not a huge amount of money,” says Skowhegan’s Lambke. “In the broad spectrum, when we think about how much we spend on Lipitor every year, it is a cheap, cheap intervention. And arguably more effective.”

Black, a former Food section staffer now based in Brooklyn, writes Smarter Food monthly. Follow her on Twitter: @jane_black.