  Background: Technology has provided a new way of life for adolescents.
Strategies aimed at improving health behaviors through digital platforms can
offer promising results. However, since peers can modify behaviors related to
food and exercise, studying digital interventions based on peer influence to
improve weight status of adolescents is important.
  Objective: To assess an eHealth app's effectiveness in adolescent population
improvements in age- and sex-adjusted BMI percentiles. The study also examined
social relationships of adolescents pre- and postintervention, identifying
group leaders to study their profiles, eating, physical activity habits, and
app usage.
  Methods: BMI percentiles were calculated following World Health Organization
guidelines. Participants' diets and physical activity levels were assessed
using the KIDMED questionnaire and PAQ-A. Social network variables were
analyzed using SNA methodology, with reciprocal friendships used to compute the
"degree" measure for centrality.
  Results: The sample included 210 individuals in the intervention group and 91
in the control group, with a 60.1% participation rate. Adolescents in the
intervention group modified their BMI toward the 50th percentile, improving
diet and increasing social network postintervention. Group leaders were also
leaders in physical activity and app usage.
