AbstractObjective:To identify dietary patterns and prospectively evaluate their influence on the BMI Z-score of adolescents.Design:A longitudinal study, using data from the Longitudinal Study on Sedentary Behavior, Physical Activity, Eating Habits and Adolescent Health – LONCAAFS.Setting:To obtain data on food consumption, a 24-h recall survey was conducted; a second 24-h recall was applied to 30 % of the sample in all waves. Dietary patterns were identified by exploratory factor analysis using principal components. BMI Z-score was determined according to the recommendation of the WHO, based on the BMI for age and sex. Socio-economic data, sedentary behaviour and physical activity level were obtained. Associations between BMI Z-score and dietary patterns and between BMI Z-score and variables of interest were determined using generalised estimating equations.Participants:Totally, 1431 adolescents were assessed in 2014, 1178 in 2015, 959 in 2016 and 773 in 2017, belonging to the public schools of João Pessoa, Northeast Brazil.Results:Three dietary patterns were identified throughout the study: ‘traditional’, ‘snacks’ and ‘Western’. The ‘Western’ dietary pattern was positively associated with BMI Z-score (β = 0·025; 95 % CI 0·002, 0·048), regardless of sex and physical activity level, prospectively.Conclusion:A dietary pattern composed of foods with high energy density, high fat and sugars, and low fibre influences the BMI Z-score of adolescents over time.