Supplementary Material for: From childhood to adolescence: Long-term trends in severe obesity in German youth (2002–2023)

Abstract
Introduction
Research on severe obesity (SO) is scarce and often contradictory. As higher weight status persists into adulthood, we aimed to analyze long-term trends in the prevalence of SO in children and adolescents in Germany using a large real-world data set. Furthermore, we analyzed subgroup differences and assessed how the COVID-19 pandemic affected weight status.

Methods
We analyzed data from the CrescNet auxological network including 1,495,401 clinical visits by 4-16-year-old children (2002-2023). Weight trends were examined with a focus on SO using logistic regression, stratified by sex and age. Effects are reported as odds ratio per 5 years (OR5) pre-pandemic and as OR for consecutive years during the pandemic. Quantile regression assessed trends of the 50th, 90th, 97th, and 99th percentiles of excess weight.

Results
Pre-pandemic, SO remained stable or declined in children under 12 until 2010: OR5: 0.8-1, p<0.001) but rose significantly afterward (OR5: 1.1-1.2, p<0.001). Children between 12-16 years of age showed a continuous increase, especially boys (boys12-16: OR5: 1.3, girls12-16: OR5: 1.1, p<0.001). During the pandemic, SO peaked in 2021 across all groups (OR21vs19: 1.3-1.7, p<0.001). By 2023, younger children returned to pre-pandemic levels, while older children, particularly 8-16-year-old girls, remained at higher weights (OR23vs19: 1.2-1.5, p<0.001-0.002). Weight gain was most prominent in SO groups but could also be seen in pre-pandemic and pandemic overweight and obesity subgroups, generally decreasing toward the end of the pandemic.

Conclusion
SO has increased over the last two decades, with the COVID-19 pandemic accelerating this trend, particularly in adolescents. While younger children recovered by 2023, excess weight in older children, especially girls, continues to escalate.