Cost-effectiveness analysis of diets may comprise an important tool to promote food security; however, studies show divergent evidence regarding the relationship between diet quality and cost in diverse populations. Thus, this study assesses differences in cost-effectiveness ratios regarding adherence to nutritional recommendations using data representative of the population level in Sao Paulo municipality, Brazil. Information from adolescents and adult individuals (n = 1742) was used to estimate diet quality and cost in 2015. Differences in cost-effectiveness ratios were investigated through application of two diet quality indexes and exploration of individuals' personal and contextual characteristics. Results indicated that higher diet cost was associated with higher adherence to nutritional recommendations at the national level and inversely associated with adherence to international recommendations. Purchasing foods in street markets was linked to healthier diets at lower costs, and protein consumption was associated with higher diet cost regardless of diet quality; however, diet quality was linked to type of protein consumed by individuals. Differences in cost-effectiveness ratios were attributable to methodological choices in measuring dietary quality (why); individuals' personal and contextual characteristics, in particular, access to retail equipment (where); and certain food choices (what). Therefore, cost-effectiveness analyses should be tailored to policy goals and local environments to ensure proper assessment of nutrition programs and to foster improvements in nutritional diet quality at lower cost.
Keywords: cost-effectiveness; diet quality; income; nutritional recommendations; street markets.