Initial findings from a small Department of Agriculture pilot program found that people on food stamps who received such incentives ate 25% more produce than who did not, equivalent to about an extra fifth of a cup (47ml) of fruits and vegetables a day.

While that may not sound like much, over the course of a month that can add up to about six extra cups (1.42 liters) of wholesome food, something officials and some nutrition experts said was a meaningful start, especially for a population struggling to eat healthily.

USDA recommends anywhere from 2 to 3 cups of vegetables and 1-1/2 to 3 cups of fruit a day for adults, depending on age and activity levels, but many struggle to reach those levels because of their relative high cost and extra preparation often needed compared to processed food.

"Many low income people face additional time and resource challenges when it comes to putting healthy food on the table that can make less healthy options seem more appealing," the agency said in the initial report.

Scott Kahan, a physician and head of the Strategies to Overcome and Prevent Obesity Alliance, said the results helped show consumers that "making the healthy choice is the easy choice."

The findings follow a 13-month pilot program of 55,000 households receiving food stamps in 2012 in Hampden County, Massachusetts, the state's poorest area. About 7,500 families were randomly assigned to be eligible to receive 30 cents back for every federal food stamp dollar spent on certain produce.

About 70% of those given refunds said they "felt that fruits and vegetables had become more affordable," USDA said.

Under the program, those in the experimental group on average got an extra $3.64 credit back after spending about $12 a month on produce. Excluding those who did not buy eligible produce, participants earned back an average of $5.55 a month for about $18.50 in fruit and vegetable purchases.

Formally known as the Supplemental Nutrition Assistance Program, or SNAP, food stamps help poor people buy groceries.

The program's cost has more than doubled and enrollment is up by 20 million people since the 2007-09 recession. Nearly one in seven Americans receives food stamps, and the average benefit is $1.50 per meal.

Besides becoming a target for budget-cutters in Congress, the program has drawn attention for what participants buy.

Critics and health advocates point to the use of food stamps to buy soda and other processed foods that they say can contribute to health problems like obesity and diabetes, costing the government more in health coverage later on.

While some lawmakers have called for limits on using food stamps to buy processed foods, the food industry opposes any restrictions. The Grocery Manufacturers Association has said such limits unfairly curb consumer choice and burden companies.

USDA Secretary Tom Vilsack said the report shows "the clear impact that promoting nutritious food choices can have on improving the healthfulness of SNAP purchases."

Other private and state-based groups have also offered varying financial incentives to those receiving food assistance, but many of those efforts are more generous and immediate.

Wholesome Wave, which connects food stamp users and other aid recipients to farmers' markets, found in its own study last year that SNAP participants given 100% in matching dollars right at the market bought 80% more produce.

"Nutrition incentives work," said Gus Schumacher, the group's vice president of policy.

It is unclear whether the pilot program, which was funded in the 2008 farm law, could be expanded. While the U.S. Senate has passed legislation to renew the law that included funding for such an effort, the House of Representatives version strips out food stamp funding altogether.

A final report on the pilot will offer a closer look on participants' shopping patterns and other details, USDA said.