Changes in body composition between 1997 and 2002 among South Australian children: influences of socio-economic status and location of residence.

OBJECTIVE: To compare rates of change in South Australian children's body composition between 1997 and 2002 in subsamples based on location of residence and socioeconomic status.
METHODS: Year 6 children from randomly selected South Australian schools in 1997 (32 schools, n=1,423) and 2002 (29 schools, n=992) were compared on: body mass index (BMI), sum of triceps and abdominal skinfolds (skinfold sum) and waist girth. Samples were partitioned into urban (population >20,000) and rural (<10,000) subsamples, and low, medium and high SES. ANCOVA, controlling for boys' decimal age and girls' predicted menarcheal age, was conducted for the whole sample, and where interactions were significant, separately in socio-demographic strata.
RESULTS: Between surveys, there were significant increases in boys' waist girth (p=0.004) and skinfold sum (p=0.007), and girls' BMI (p=0.0005) and skinfold sum (p<0.0001). There were significant interactions of survey year and sociodemographic variables among girls only. While there were no significant changes in anthropometric variables among rural and high SES girls, urban girls increased in skinfold sum (p<0.0001), waist girth (p=0.033) and BMI (p=0.0007). Low (p<0.0001) and medium (p=0.001) SES girls' skinfold sum increased between surveys.
CONCLUSIONS: Secular trends in Australian children's body fatness are continuing. Further, the rates of change in girls are affected by the socio-demographic milieu. IMPLICATIONS: The development of targeted interventions to combat child obesity will depend on a clearer understanding of how environmental influences on weight status are distributed across the sociodemographic landscape.