Are Economic Incentives Useful for Improving Dietary Quality Among WIC Participants and Their Families?

Year: 2004

Research Center: Department of Nutrition at the University of California, Davis

Investigator: Herman, Dena, Gail Harrison, Abdelmonem Afifi, and Eloise Jenks

Institution: University of California, Los Angeles

Project Contact:
Dena R. Herman
Division of Cancer Prevention and Control Research
UCLA/Jonsson Comprehensive Cancer Center and
UCLA School of Public Health
Los Angeles, CA 90095
Phone: 310-206-9924


Dietary quality, as measured by fruit and vegetable intake, is a powerful protective factor against a number of common chronic diseases, including several causing premature death and disability. Low income is well-established as a risk factor for poor dietary quality in the United States. The Special Supplemental Nutrition Program for Women, Infants and Children (WIC) program provides a context for investigating means to improve fruit and vegetable consumption in a vulnerable population.

WIC was designed and developed before the relationship of fruit and vegetable intake to chronic disease risk was well-established, and the foods were selected to supplement the nutrients that were thought to be most limited in the diets of low-income women and children, namely protein, calcium, vitamin A, and vitamin C. Recently, there has been discussion about adding fruits and vegetables to the WIC food package, potentially on a cost-neutral basis. A recent report by the Institute of Medicine reviewed the current public health context for the development of WIC food packages and proposed criteria for the inclusion of food items. Fruits and vegetables were among the highest priority food groups. This research investigated whether providing supplemental financial support targeted for purchase of fresh fruits and vegetables would result in high uptake of the supplement and whether the individuals would continue to consume more fruits and vegetables after financial support was discontinued.

A nonequivalent control group design was used to provide vouchers for fresh fruits and vegetables to low-income women participating in the Public Health Foundation Enterprises WIC program in Los Angeles, CA. The study recruited 602 women who were enrolling for postpartum services at three selected WIC program sites (approximately 200 per site). Sites were assigned to: intervention with vouchers redeemable at a local supermarket; intervention with vouchers redeemable at a nearby year-round farmers' market; and a control site with a minimal nonfood incentive for participation in interviews. Vouchers were issued bimonthly, at the level of $10 per week. Interventions were carried out for 6 months, and participants’ diets were followed for an additional 6 months after the intervention. Quantitative 24- hour dietary recalls were conducted at four interviews for each participant.

At the intervention sites, two extra interviews spaced 2 months apart were held to obtain information on the fruits and vegetables purchased with the vouchers. Specifically, participants were asked to respond to the question “What did you buy with your fruit and vegetable coupons last week?” Voucher redemption rates were obtained from scanned data from the supermarket’s corporate headquarters. In the farmers’ markets, vouchers presented for purchase were collected by the farmers’ market manager and turned into the city government’s accounting department for tallying. Vouchers were then mailed to the study’s research staff, who re-counted the redeemed vouchers and logged the tallies into an electronic database.

In all, $44,000 worth of vouchers were issued for the supermarket and $44,960 for the farmers’ market. Redemption rates were 90.7 percent for the farmers’ market and 87.5 percent for the supermarket. Overall, participants reported purchasing 27 and 26 different fruits, and 34 and 33 different vegetables in the farmers’ market and supermarket outlets, respectively. Five fruits and five vegetables accounted for about 70 percent of the items reported for each group. The 10 most frequently reported items were oranges, apples, bananas, peaches, grapes, tomatoes, carrots, lettuce, broccoli and potatoes. A larger number of item purchases were reported for the farmers' market although the total number of types of fruits and vegetables did not differ significantly between the two market settings.

Participation in the interventions increased consumption of fruits and vegetables with use of the supplement and that increase was sustained 6 months after the intervention. At baseline, participants at the farmers’ market reported eating 2.2 servings/1,000 kilocalories (kcal) on average, 2.9 servings/1,000 kcal at the supermarket site, and 2.6 servings/1,000 kcal at the control site. Six months postintervention, this same comparison was made, and the increase in participant fruit and vegetable intake reported by intervention site was sustained. Participants at both the farmers’ market and supermarket sites reported eating 4.0 servings of fruits and vegetables/1,000 kcal on average, while control site participants reported eating 3.1 servings/1,000 kcal on average. The difference in consumption between each of the intervention sites and the control site was statistically significant even after adjusting for multiple factors. The results were unaffected when evaluating consumption of fruits and vegetables excluding beans and potatoes, and fruits and vegetables excluding juices. Increases in vegetable consumption were primarily responsible for the overall increases in fruit and vegetable intake.

A linear regression analysis using baseline demographics, government program participation, body composition, food security status, reported energy intake, reported fruit and vegetable intake, infant feeding method, and treatment site explored which of these factors were associated with fruit and vegetable intake six months post-intervention. The results indicated that higher reported intake of fruits and vegetables 6 months postintervention was associated with reported fruit and vegetable intake at baseline, preference for speaking Spanish, and participating at either the farmers’ market site or the supermarket site compared to the control site.

In summary, the variety of choices of fruits and vegetables exhibited in this study leads to the conclusion that, in this setting, low-income consumers make varied and nutritious choices from available produce. The findings point to the potential for dietary improvement with a targeted subsidy that allows free choice within the fresh produce category. Neither the supermarket nor the farmers’ market found the study particularly burdensome, and both outlets were positive about their participation. No specific barriers arose to voucher redemption by participants or retailers. In addition to the economic intervention, the high intake of fruits and vegetables may be attributed to the large proportion of Latinos included in the study population. The study participants’ sustained intake of fruits and vegetables may reflect retained cultural food behavior habits and the study’s timing at a critical point in a family—the birth of a child and the surrounding concern for a healthy child.