Background: The COVID-19 pandemic has exacerbated the obesity epidemic, with both adults and children demonstrating rapid weight gain during the pandemic. However, the impact of having a COVID-19 diagnosis on this trend is not known.

Methods: Using longitudinal data from January 2019 to June 2023 collected by the US National Institute for Health's National COVID Cohort Collaborative (N3C), children (age 2-18 years) with positive COVID-19 test results (n=11,474, 53% male, mean [SD] age 5.57 [±3.29] years, 54% white, mean [SD] 5.2 [±2.9] BMI observations per participants) were matched with COVID-19 negative children with identical demographic characteristics and similar observation window. We compared BMI percentile trajectories between the COVID-19 positive and COVID-19 negative cohorts, with further evaluation performed on COVID-19 positive patients stratified by hospitalization status.

Results: COVID-19 positive patients had a greater increase in %BMIp95 than COVID-19 negative patients (average increase of 2.34 (±7.73) compared to 1.46 (±6.09), p<0.0005). COVID-19 positive patients gained more weight after their diagnosis of COVID-19 than before. Non-hospitalized children gained more weight than hospitalized children (average increase in %BMIp95 of 2.38 (±7.65)) compared to 1.87 (±8.54)). Mixed effect regression analyses demonstrated that these associations remained even after adjusting for time, demographics, and baseline %BMIp95.

Conclusions: Having a COVID-19 diagnosis was associated with more rapid weight gain, especially after diagnosis and early in the pandemic. Future research should explore the reasons for this association and the implications for future health emergencies.