ObjectiveThe present study aimed to assess the relationship between dietary habits, change in socio-economic status and BMIZ-score and fat mass in a cohort of South African adolescents.DesignIn the longitudinal study, data were collected at ages 13, 15 and 17 years on a birth cohort who have been followed since 1990. Black participants with complete dietary habits data (breakfast consumption during the week and at weekends, snacking while watching television, eating main meal with family, lunchbox use, number of tuck shop purchases, fast-food consumption, confectionery consumption and sweetened beverage consumption) at all three ages and body composition data at age 17 years were included in the analyses. Generalized estimating equations were used to test the associations between individual longitudinal dietary habits and obesity (denoted by BMIZ-score and fat mass) with adjustments for change in socio-economic status between birth and age 12 years.SettingBirth to Twenty (Bt20) study, Soweto-Johannesburg, South Africa.SubjectsAdolescents (n1298; 49·7 % male).ResultsIn males, the multivariable analyses showed that soft drink consumption was positively associated with both BMIZ-score and fat mass (P< 0·05). Furthermore, these relationships remained the same after adjustment for socio-economic indicators (P< 0·05). No associations were found in females.ConclusionsLongitudinal soft drink consumption was associated with increased BMIZ-score and fat mass in males only. Fridge ownership at birth (a proxy for greater household disposable income in this cohort) was shown to be associated with both BMIZ-score and fat mass.