OBJECTIVE:To investigate associations between body mass index (BMI) and family characteristics, including lifestyle, in parents and offspring from Australian families. DESIGN AND SUBJECTS: Longitudinal survey of 219 families of Australian children who had been surveyed 3-yearly between the ages of 9 and 18 y. MEASUREMENTS: Socio-economic status, weight and height, diet from 3 day records or food frequency questionnaires, alcohol consumption, smoking habits and physical ®tness in offspring (bicycle ergometry in 18-y-olds). RESULTS: In 18-y-olds, in models examining offspring's lifestyle variables, BMI was predicted negatively by physical ®tness (P 0.012), and positively by alcohol intake (P 0.046) in sons while, in daughters, only a negative association with physical ®tness was signi®cant. In models including parental characteristics, BMI in 18-y-old sons and daughters was signi®cantly predicted by mothers' and fathers' BMI, independently of offsprings' alcohol intake, smoking, physical ®tness and parents' education, and, in daughters, by fathers' alcohol intake. These models explained 48% of variance in daughters and 33% in sons. In both sons and daughters, BMI over the 9 y of the survey was consistently higher in offspring with overweight or obese fathers (P 0.033 for sons, P 0.024 for daughters) or mothers (P 0.031 for sons, P 0.037 for daughters). Physical ®tness at the ages of 12, 15 and 18 y was negatively related to fathers' obesity in daughters and mothers' obesity in sons. Obesity in fathers was associated with a four-fold increase in risk of obesity at the age of 18 y in both sons and daughters with an independent eightfold increase in risk for daughters if mothers were obese. Birthweight was unrelated to overweight or obesity in the 18-y-olds. Alcohol intake in sons related signi®cantly to alcohol intake in either parent while, for daughters, there was a signi®cant association only with fathers' alcohol consumption. In daughters, fat intake was positively associated with fat intake score in both fathers and mothers. CONCLUSION: Parental overweight or obesity may identify children at risk for a range of unhealthy behaviours. Promotion of a healthy lifestyle targeting overweight families, particularly in lower socio-economic groups, should be a priority.
