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Are the rising prices of fruits and vegetables driving America's obesity epidemic? New research shows lowering the costs of healthy foods and supermarkets increases the consumption of fruits, vegetables and whole grain foods and decreases the consumption of unhealthy, nutritionally less-desirable foods.

Researchers from the RAND Corporation, a non-profit based in Santa Monica, California that helps improve policy and decision-making through research and analysis, studied a program available to members of South Africa's largest private health insurance company that gives a rebate of 10 percent or 25 percent on purchases of healthy foods. The program began in 2009 and now has about 800 participating supermarkets and 260,000 households.

Researchers noted that in the United States and other parts of the world, more and more people are interested in the idea of improving diets with food discount programs.  In 2008, U.S. Congress approved funding for a demonstration of the concept and both employers and insurance companies in the U.S. are beginning to test the approach.

The program in South Africa allows shoppers to get rebates on foods that have been selected by a panel of nutritionists, physicians and behavioral scientists.  The list of approved foods has over 6,000 items and accounts for 20 percent of food spending at supermarkets. Approved foods are marked at supermarket shelves and include fruits and vegetables, whole grains, nonfat dairy, but does not include most items with added sugars or salt.

Researchers collected data from supermarket scanners linked to 170,000 households and survey data about diet patterns from 350,000 individuals.  Survey respondents included those who participated in the rebate program in those who did not.

Researchers found that regardless of how the information was analyzed, lower prices for healthy foods were strongly linked to better self-reported diet, according to the study published March in the American Journal of Preventive Medicine.

Specifically researchers found that a rebate of 25 percent increased the ratio of healthy to total food purchase by 9.3 percent.  Furthermore, the discount increased the ratio of fruit and vegetables to total food purchases by 8.5 percent and decreased the ratio of less healthy food items to total food purchases by 7.2 percent.

Less health food items include cookies, candy, chips and soft drinks. 

Researchers noted that the effects of the price subsidies appeared stable over time and a greater rebate had consistently greater impact than the smaller rebate.

"These findings offer good evidence that lowering the cost of nutritionally preferable foods can motivate people to significantly improve their diet," Roland Sturm, a study co-author and a senior economist at RAND, said in a news release.

"But behavior changes are proportional to price changes. When there is a large gap between people's actual eating behaviors and what nutritionists recommend, even a 25 percent price change closes just a small fraction of that gap," he added.

After analyzing the self-reports, researcher found that people who received a 25 percent rebate consumed an additional half-serving of fruits and vegetable each day.  These people were also less likely to consume fast food, foods high in sugar and salt, friend foods and processed meats. However, researchers noted that there was no evidence that the rebate program reduced rates of obesity.  The findings from the survey were published in the January issue of the American Journal of Health Behavior.