Abstract
The present study aimed to assess the relationship between dietary habits, change in socio-economic status and BMI Z-score and fat mass in a cohort of South African adolescents. In 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 BMI Z-score and fat mass) with adjustments for change in socio-economic status between birth and age 12 years. Birth to Twenty (Bt20) study, Soweto-Johannesburg, South Africa. Adolescents (n 1298; 49·7 % male). In males, the multivariable analyses showed that soft drink consumption was positively associated with both BMI Z-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. Longitudinal soft drink consumption was associated with increased BMI Z-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 BMI Z-score and fat mass.
Highlights
Dietary habits data for all three ages were assessed against body composition outcomes at age 17 years
No differences were found in the ownership of a TV, fridge or landline telephone or in maternal education
At 17 years of age, females were shorter than males (P, 0?001) with a similar weight; their mean BMI was greater than that of males (P, 0?001)
Summary
Design and sample size Data for the present study were obtained from a longitudinal birth cohort study, the Bt20 cohort, which started in 1989(11). Dietary assessment and exposure variables Participants completed interviewer-assisted questionnaires on dietary behaviours around food choices and eating practices, occurring in the home, school and community, that have been shown to be associated with poor nutritional outcomes[14,15,16,17,18,19,20,21,22]. Confounding was assessed by performing the regression of individual household SES variables (collected at birth) v. For each SES variable a new variable was created to assess the change in SES between birth and age 12 years; that is, if the participant ‘acquired’ a particular household durable between the two time points or if they ‘never’ had that particular household durable over the two time points These two variables were compared with the reference variable of ‘always’ having a particular household durable over the two time points. Individual dietary habit variables were inserted individually into the statistical model; if significantly associated (P , 0?05), multivariable analysis was carried out with the inclusion of the confounding household durable variables (previously assessed by univariate analysis)
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