ABSTRACT Objective To determine the sustainability of food quality in an obesity-prevention strategy for adolescent girls. Methods The study is a randomized controlled trial with 253 girls (Mean=15.61, 95% Confidence Interval 15.51-15.72) enrolled in 10 vocational schools in São Paulo. The diet intake was determined using a “Food Frequency Questionnaire” and analyzed according to the Brazilian Healthy Eating Index-Revised adequacy, moderation, and overall scores. The adolescents’ dietary intake was compared to the baseline 6 months and 12 months post-intervention. Descriptive statistics and analyses of covariance were used, considering a 5% significance level. Results Significant increases were found on the components total fruits (F=6.98, p<0.01), total vegetables (F=5.76, p=0.02), beans (F=5.96, p=0.02), and whole cereals (F=12.35, p<0.001). However, there was also a significant decrease on the scores for milk and dairy (F=6.48, p=0.02), and oils (F=5.98, p=0.02). At 12-month post intervention, improvement on the overall score was found (F=3.89, p=0.05), but there was a decrease on the component whole cereals (F=11.85, p<0.001), as well as in milk and dairies (F=6.38, p=0.02). Despite no significant effect for the SoFAAS component, a moderate effect size was revealed (d=0.56). Conclusion There were significant effects on some diet quality components and for the overall scores at 6-month and 12-month post intervention. Therefore, sustainable dietary changes should be the focus of obesity prevention programs for adolescents. Socio-economic influences on diet behaviors would also need to be acknowledged.