Over the past few decades, there has been a worldwide increase in the mean body mass index (BMI), and the percentage of overweight and obese persons. Various studies have shown a relationship between parents’ BMI and their children’s BMI. In addition, studies have shown that the BMI is inversely related to physical activity, and reduced physical activity has been identified as a major factor in increasing body weight. Other factors that have been reported as affecting body mass include educational level and smoking status. Although there are studies assessing the impact of these risk factors on body mass, none has evaluated these factors from adolescence into adulthood. Kvaavik and associates tracked the BMI from adolescence to adulthood in a group of persons and examined the effect of identified risk factors for obesity. They also evaluated changes in lifestyle factors as predictors of adult obesity.

The study was a longitudinal tracking of a cohort of persons from six schools in Oslo, Norway over a period of 18 to 20 years. The baseline data were collected during 1981 when the children were at an average age of 13 years (age range: 11 to 16 years). The data collected at baseline and at follow-up in 1999 included height and weight measurements, sexual maturation, physical fitness, leisure time physical activity, and smoking status. The parents were assessed at the same times by questionnaires that included height, weight, and education level. The change in BMI was divided into three categories: (1) 1 to 3 BMI quartiles lower; (2) no change; and (3) 1 to 3 BMI quartiles higher.

The tracking of BMI from age 15 to 33 was high. The adolescent’s BMI, the father’s BMI, the subject’s own leisure time physical activity, adult smoking, and sex explained a significant degree of the variation of the adult BMI. The participants who had a higher BMI as an adolescent had the highest risk for having an adult BMI of 30 or greater. Participants who were in the lowest two quartiles of BMI at adolescence were less likely to have a high adult BMI. Participants who increased their leisure time physical activity from adolescence into adulthood were less likely to be obese compared with those whose activity level was stable or decreased over the study period. Participants who stopped smoking during the study period were more likely to have a higher BMI than those who continued to smoke.

The study findings suggest that adult body weight is directly related to adolescent body weight. Change in leisure time physical activity over the same time period can predict the risk for being overweight as an adult. According to the authors, the implication of this study is that physical activity should be emphasized during adolescence and should include the parents.