Obesity: A Need to Intervene During Adolescence

The transition period between adolescence and young adulthood should be a target time for intercepting obesity, according to researchers at the University of North Carolina at Chapel Hill (Am J Clin Nutr 2004;80:569). Results from their recent study showed that the proportion of teens who became obese as teens and remained obese as adults was very high.

Dr. Penny Gordon-Larsen and co-workers used nationally representative, longitudinally measured height and weight data collected from U.S. adolescents enrolled in wave II (1996, ages 13-20) and wave III (2001; 19-26 years) of the National Longitudinal Study of Adolescent Health, which followed nearly 10,000 adolescents through adolescence and young adulthood.

Discrepancies between definitions of obesity

One of the first problems the researchers encountered was the discrepancy between adolescent and adult definitions of obesity, which made calculating the incidence of obesity between adolescence and adulthood very difficult. For example, an 18-year-old girl with a body mass index (BMI) of 30.2 would not be considered overweight according to the age- and sex-specific Centers for Disease Control and Prevention growth charts; in this case, her BMI would be less than the 95th percentile. If her height and weight did not change and she had the same BMI at age 21, she would be classified as obese.

Study group

The study group included more than 20,000 teens enrolled in Add Health, a longitudinal, nationally representative, school-based study of U.S. teens in grades 7-12 plus selected oversampled groups, including certain minority groups, such as blacks from well-educated families. Wave II included 14,438 eligible students from the first wave, teens who would still be enrolled in high school. Wave III included 15,197 eligible original respondents. Heights and weights were measured during in-home surveys using standardized procedures.

Who was obese?

Overall, 22.1% of the wave III young adults (mean age 21.4 years) had a BMI of =30. In comparison, at wave II, 10.9% of the group had been obese. The prevalence of obesity was highest among non-Hispanic black and Hispanic young adult females. At wave III, extreme obesity (BMI =40) was 4.3% for the total population. Over the 5-year period between ages 12-20, and ages 19-26, marked differences in the incidence and reversal of obesity were observed. Of the total sample, 9.4% were obese as teens and young adults, and 12.7% of those who were not obese at wave II became obese at wave III. Non-Hispanic black females were significantly more likely than their non-Hispanic white counterparts to become and remain obese, whereas Asians were signficantly less likely to become and remain obese.

The authors note that their results mirror those from many smaller studies, which show a significant tendency for childhood and adolescent overweight to persist into adulthood. Childhood obesity is moderately predictive of obesity during adulthood, whereas adolescent obesity is highly predictive of adult obesity. They also note that the public health implications of this upward trend in obesity are substantial, including higher rates of diabetes and nutrition-related chronic degenerative diseases appearing at ever-younger ages. Minority groups, particularly black women, are at special risk. This trend calls for preventive strategies and programs to intervene during the time of highest risk, between adolescence and young adulthood, according to the authors.