Grocery coupons aren't associated with nutritious food. Big chains use them to lure you into the store, offering discounts mostly on processed food and snacks. When researchers looked at 1,056 coupons available online for supermarkets nationwide , they found that the largest share (25 percent) were for "processed snack foods, candies and desserts." Another 14 percent offered price breaks on prepared meals, 11 percent were for cereals, and 12 percent were for beverages, more than half of which were sodas, juices and energy or sports drinks.

Just 3 percent offered discounts on vegetables, 1 percent were for unprocessed meats, and fewer than 1 percent provided breaks on fruit prices. And those fruits were canned, not fresh.

If stores make "the unhealthier option less expensive and easier to purchase, we can't be surprised when [people] purchase it," said Andrea Lopez, a research analyst at the University of California-San Francisco School of Medicine, who  helped conduct the study. It was published in March in the Centers for Disease Control and Prevention's journal, Preventing Chronic Disease.

FILE - In this Aug. 3, 2005 file photo, Chiquita bananas are on display at a grocery store in Bainbridge, Ohio. Fruit supply companies Chiquita of the United States and Fyffes of Ireland said Monday, March 10, 2014, they had agreed to merge to create the world's biggest banana supplier. (AP Photo/Amy Sancetta, File) (AP Photo/Amy Sancetta)

But what if someone turned that model on its head and offered coupons for healthful food? Someone has, and it's a private company, not the government or a nonprofit. The marketing company Linkwell Health says that in a recent experiment it was able to "nudge" -- its word, not mine -- people out of the prepared food aisles and toward the fruits and vegetables.

Linkwell sent coupons, recipes and information on healthful diets to 24,000 people enrolled in a health insurance plan (which its report doesn't name.) The recipients were people with chronic health problems such as Type 2 diabetes that are, in part, associated with poor diets.

Linkwell knew from surveys that people have higher opinions of supermarkets than they do of health insurers (I could have told them that, too), mostly because of customer loyalty programs that the big chains employ.

The company said it found that it was able to improve purchases of nutritious food such as fruits, vegetables, lean meats and seafood by 4.5 percent in 2012 over 2011. Not a huge gain, but certainly one that might be worth trying, since supermarkets sent out 305 billion coupons that year anyway.

Without coupons, "if we ask them to go get a bushel of fresh produce, we might as well ask them to go to Shanghai than to move from the center of the store to the produce aisle," said Ben Gardner, founder and president of Linkwell Health, which is based in Boston. With the coupon and information experiment, "not only are we getting them to change the way they eat, but they feel better about themselves and they feel better about their health plan."

I have to point out that Linkwell's results aren't published in a journal or peer-reviewed, so I'm relying on the company's report, which Linkwell sent me when I asked for it.

But there is some precedent in the research. When public health researchers in San Diego County gave poor people enrolled in government food-assistance programs an extra $20 as long as they spent it on fruits and vegetables at one of five different farmers markets, they reported large gains in purchases of those foods. In one group that participated for three to six months, consumption of five daily servings of fruits and vegetables rose 5.9 percent. In another, surveyed after 12 months, the number of people who had adopted that habit rose 4.8 percent. And the farmers markets reaped large gains in customer spending. The study was published in Preventing Chronic Disease in November.

Lopez, the UCSF researcher, said it's very clear that "the food environment really affects people's eating habits."