Objective: The aim of this study was to evaluate the impact of coronavirus disease 2019 (COVID-19) lockdown on body mass index (BMI) z-score of adolescents treated for obesity, and to assess the correlation between BMI z-score changes and lifestyle variables.

Methods: This cross-sectional study recruited 66 participants aged 11-18 years with overweight or obesity who attended our obesity clinics before and after the lockdown. We assessed demographic and anthropometric characteristics as well as lifestyle variables.

Results: The mean BMI z-score of the participants was stable during this period (p = 0.233). Balanced diet, snacking, and sweet beverage consumption improved in about half of the participants. Having at least one parent at home was associated with a significantly more balanced diet (p = 0.008) and an increase in family activities (p = 0.015). Physical activities decreased (51.5%) and screen time increased for most of the adolescents (86.4%). The BMI z-score decreased significantly when three or more lifestyle habits improved (p<0.001).

Conclusions: This study showed that BMI z-scores were stable for a majority of adolescents treated for obesity during the COVID19 lockdown, along with positive and negative changes on weight-related lifestyle habits. This extraordinary period may have created opportunities for lifestyle modification and has emphasized the importance of family support in the management of obesity in adolescents.