Thao-Ly Phan, MD, MPH, discusses weight lessons learned during COVID-19 pandemic

Children who contracted COVID-19 gained weight more rapidly than their peers during the pandemic, according to new findings published in Childhood Obesity. The study used longitudinal data from the National COVID Cohort Collaborative (N3C) to track body mass index (BMI) trajectories of over 11,000 children with a COVID-19 diagnosis, comparing them with a matched cohort of COVID-negative peers.

Thao-Ly Phan, MD, MPH, medical director of the Healthy Weight and Wellness Clinic at Nemours Children’s Health and study coauthor, said the work builds on early pandemic observations.

“We knew early on that the pandemic impacted weight for both children and adults,” Phan explained, noting earlier reports from Kaiser and the CDC that documented sharp rises in overweight and obesity among children. “I think now we’re starting to figure out why.”

The study found that both COVID-positive and COVID-negative children gained weight during the pandemic, but those with COVID gained significantly more. On average, the COVID-positive group had a greater increase in BMI percentile compared to their peers, with the most rapid gain occurring after diagnosis. Non-hospitalized children saw greater increases than those who were hospitalized, a trend that held even after adjusting for demographics, baseline weight status, and observation period.

“We contributed uniquely to the literature by asking: ‘Does having a diagnosis of COVID impact the weight gain that we know happened for all children during the pandemic?’” Phan said. Leveraging the N3C database—which harmonizes electronic health records from more than 90 US-institutions—the team was able to compare matched groups and evaluate weight trajectories before and after infection. Although the study could not determine the exact reasons behind the association, Phan pointed to several likely contributors.

“Some recent studies have shown that children were more sedentary, had abnormal eating patterns, and experienced disrupted routines,” she said. “Altogether, I think this gives us a deeper picture of why children may have gained weight during the pandemic, and how we might prevent future weight gain in children."

Reference:

Mottalib M, Phan TL, Bramante CT, Chute CG, Pyles LA, Beheshti R. Impact of COVID-19 Diagnosis on Weight Trajectories of Children in the US National COVID Cohort Collaborative. Childhood Obesity. Published online May 26, 2025. Accessed September 12, 2025. https://www.liebertpub.com/doi/10.1089/chi.2024.0256