Higher nutritional quality at no additional cost among low-income households: insights from food purchases of "positive deviants".

BACKGROUND: It is unknown whether diet quality is correlated with actual food expenditure. According to the positive deviance theory, the study of actual food expenditure by people with limited economic resources could help identify beneficial food-purchasing behavior.

OBJECTIVES: The aims were to investigate the relation between actual expenditure on food and nutritional quality and to identify "positive deviants" among low-income households.

DESIGN: Individuals in deprived social situations (n = 91) were recruited as part of the "Opticourses" nutrition intervention conducted in 2012-2014 in poor districts of Marseille, France. Opticourses participants collected food-purchase receipts for their household over a 1-mo period. "Actual diet costs" and "estimated diet costs" were calculated per 2000 kcal of food purchases by using actual expenditures and a standard food price database of food consumed by a representative sample of French adults, respectively. Mean adequacy ratio (MAR), mean excess ratio (MER), and energy density (ED) were used as nutritional quality indicators. "Positive deviants" were defined as having a higher MAR and a lower MER than the respective median values.

RESULTS: Opticourses participants selected less-expensive food options than the average French population, both within a food group and for a given food item. Higher diet costs were associated with higher nutritional quality (higher MAR, lower ED), regardless of whether costs were calculated from actual expenditure or on the basis of standard food prices. Twenty-one positive deviants were identified. They made significantly healthier purchases than did other participants (MAR: +13%; MER: -90%. ED: -22%) at higher estimated diet costs. Yet, they did not spend more on food (having the same actual diet costs), which showed that they purchased food with a higher nutritional quality for their price.

CONCLUSION: In this low-income population, actual diet cost was positively correlated with nutritional quality, yet the results showed that higher diet quality is not necessarily more costly when foods with higher nutritional quality for their price are selected. The Opticourses intervention was registered at clinicaltrials.gov as NCT02383875.