Lockdown due to COVID-19 pandemic has forced a decrease in physical activity (PA), an increase in sedentary behavior (SB) and a possibly worsening of fat accumulation in already obese subjects.

The aim of this study was to investigate how social restriction may have contributed to weight changes in adolescents with obesity. Secondary aim was to evaluate possible parameters influencing weight changes.

Parameters of 51 obese adolescents were compared between two visits: within 2 months before 8 March, start of lockdown, and within 40 days after the end of it.

Mean weight gain during lockdown was 2.8���3.7�kg (p�<�0.001). Weight increase was higher in males than in females (3.8���3.4�kg vs 1.2���3.7�kg, p�=�0.02). The hours dedicated to SB increased (+2.9���2.8�h/day; p�<�0.001) while the hours of PA decreased (−1.0���1.6�h/week; p�<�0.001). Males spent more hours in SB than females (+3.8���2.7�h/day vs +1.5���2.5�h/day; p�=�0.003). There were minor changes in diet during lockdown. The most significant variables influencing both delta BMI and waist/height ratio increase were hours devoted to SB during lockdown and differences in mild and moderate PA before and after lockdown.

Obese adolescents showed a worsening of obesity during lockdown, with males mainly affected, mainly due to a reduced mild PA and increased hours spent in SB.