Physical activity, food selection and the longitudinal association with adiposity among South African school children

Background: The global pandemic of paediatric obesity, physical inactivity and unhealthy diets are important future health challenges.
Purpose: To determine 4-year changes in physical activity (PA) and food selection, and the association with adiposity among South African children.
Methods: School children aged 5 to 9 years old in 2017 (n=920) were followed up four years later (2021-2022). PA was determined by accelerometry (Actigraph). Parents indicated selection from healthy and unhealthy food groups in a validated questionnaire. Weight and height of the children were measured, and WHO BMI z-score (BAZ) was calculated. Percentage body fat (%BF) was determined using bio-electric impedance analysis. Changes in PA, frequency of food selection, BAZ and %BF from baseline to end were assessed. Associations between PA and BAZ at baseline and end, and the association between PA, frequency of food selection, age, and household income with 4-year change in BAZ was determined.
Results: Moderate and vigorous PA (MVPA) decreased over four years, while sedentary time and BAZ increased (all P<0.001). MVPA correlated negatively with BAZ and %BF. The frequency of selection from most food groups remained unchanged. The frequency of sugar-sweetened beverages intake decreased, while the intake from fast-foods showed a trend of an increase. Food selection variables showed no association with the increase in BAZ. In a regression model trends of negative associations were found between age (ß= -0.16, p=0.058) and MVPA (ß= -0.15, p=0.07), respectively, with 4-year change in BAZ.
Conclusions: PA showed a stronger association with increasing adiposity among school children, than socio-demographic variables or food selection.
Practical implications: The declining PA of school children in South Africa needs to be addressed. Policies to control food marketing and sugar-sweetened beverages sales are in place, but none to promote PA.
Funding: South African Medical Research Council and National Research Foundation of South Africa.