Plasma FA composition is associated with weight status in healthy adolescents. High intake of long-chain PUFAs, especially n-3 PUFAs, may protect obese subjects against MS and low-grade inflammation as early as adolescence.

Background: Population-based studies directed at promoting physical activity in youth have shown limited success in obesity prevention. Objective: To assess whether an intervention integrating environmental changes to induce sustained changes in physical activity, prevents overweight in adolescents. Design: Four-year randomized trial started in 2002 in eight middle schools of Eastern France. The intervention, randomized at school level, was designed to promote physical activity by changing attitudes through debates and attractive activities, and by providing social support and environmental changes encouraging physical activity. Subjects: Nine hundred and fifty four 12-year-old six-graders. Measurements: Body mass index (BMI), body composition, physical activity by questionnaire, plasma lipids and glucose, insulin resistance. Results: Intervention students had a lower increase in BMI (P ¼ 0.01) and age-and gender-adjusted BMI (Po0.02) over time than controls. The differences across groups of the age-and gender-adjusted BMI changes (95% confidence interval (CI)) were À0.29 (À0.51; À0.07) kg/m 2 at 3 years, À0.25 (À0.51; 0.01) kg/m 2 at 4 years. An interaction with baseline weight status was noted. The intervention had a significant effect throughout the study in initially non-overweight adolescents (À0.36 (À0.60;À0.11) kg/m 2 for adjusted BMI at 4 years), corresponding to a lower increase in fat mass index (Po0.001). In initially overweight adolescents, the differences observed across groups at 2 years (-0.40 (À0.94; 0.13) kg/m 2 for adjusted BMI) did not persist over time. At 4 years, 4.2% of the initially non-overweight adolescents were overweight in the intervention schools, 9.8% in the controls (odds ratio ¼ 0.41 (0.22; 0.75); Po0.01). Independent of initial weight status, compared with controls, intervention adolescents had an increase in supervised physical activity (Po0.0001), a decrease of TV/video viewing (Po0.01) and an increase of high-density cholesterol concentrations (Po0.0001). Conclusion: Enhancing physical activity with a multilevel program prevents excessive weight gain in non-overweight adolescents. Our study provides evidence that prevention of obesity in youth is feasible.

BACKGROUND AND OBJECTIVE: Waist circumference (W) has been shown to be a good predictor of cardiovascular risk. The aim of this study was to investigate whether physical activity (PA) is related to W in adolescents as previously shown in adults. DESIGN AND SUBJECTS: Cross-sectional population-based survey of 2714 12-y-old adolescents from the eastern part of France. MEASUREMENTS: Body mass index (BMI) and W were measured. Structured PA, active commuting to and from school and sedentary activities (SED), for example television viewing, computer/video games and reading and different potential confounders (dietary habits, parental overweight, family annual income tax and educational level) were assessed by a questionnaire. RESULTS: The adolescents had a mean BMI of 19.073.4 kg/m 2 , and 20.2% of them were overweight, with no gender difference. Boys had a greater W than girls (67.679.1 vs 65.778.9 cm, Po0.0001). In all, 42% of the girls and 25% of the boys did not practice any structured PA outside school and less than 40% of the adolescents commuted actively to school more than 20 min/day. About one-third of the adolescents devoted more than 2 h/day to SED. In univariate analyses, BMI was negatively associated with structured PA but significantly only for girls (Po0.01) and positively associated with SED for both genders (Po0.0001 for girls, Po0.01 for boys). W was negatively associated with structured PA and positively associated with SED both in girls (Po0.0001 and P ¼ 0.03, respectively) and boys (Po0.01 and P ¼ 0.08, respectively). Multiple general linear models show that SED is associated with BMI, independently of structured PA, in both genders. On the other hand, structured PA was inversely associated with W, independently of SED. The inverse relation between structured PA and W persisted after additional adjustment on BMI, with a greater effect of PA for the adolescents with higher BMI. CONCLUSIONS: In 12-y-old adolescents, structured PA is inversely associated with W, an indicator of total adiposity but also more specifically of abdominal fat. This suggests that PA may have a beneficial effect on youth metabolic and cardiovascular risks, in particular in the presence of overweight.