Introduction
The most commonly performed bariatric procedures worldwide are Roux-en-Y gastric bypass(RYGB) and sleeve gastrectomy(SG), yet outcomes following these procedures in young adults are limited. Therefore, the objective of this study was to compare weight loss outcomes between RYGB and SG in young adults.

Methods
This is a nationwide retrospective cohort study of young adults, aged 18-25 years, who underwent RYGB or SG between 2015 and 2019, with data from the Dutch Audit Treatment of Obesity(DATO). The primary outcome was weight loss expressed as percentage total weight loss(%TWL) in a period of three years after surgery. Secondary outcomes were successful weight loss(≥20% TWL), the incidence of complications(<30 days), and progression of obesity-related comorbidities.

Results
In total, 2,313 young adults were included, 1,246 in the RYGB group(53.9%) and 1,067 in the SG group(46.1%). Percentage TWL was significantly higher in the RYGB group compared to the SG group at one, two and three years after surgery(respectively 2.4%, 2.9% and 3.3% higher, p<0.001). In the RYGB group, 95.7% of the young adults achieved successful weight loss two years after surgery, compared to 88.7% in the SG group(p < 0.001). Strikingly, LMM revealed that RYGB in female young adults was associated with an on average 2.75% higher TWL in comparison with SG(p<0.001), whereas this effect was not seen in male young adults(B=0.63, p=0.514). No differences were found in the incidence of complications, nor in the progression of obesity-related comorbidities except for gastroesophageal reflux disease(GERD). There was more improvement or resolution of GERD in the RYGB group (95.2% vs. 56.3%, p<0.001).

Conclusion
Population-based data revealed that similar numbers of RYGB and SG were performed in young adults in the Netherlands, and appeared to be safe. On the short- and midterm RYGB was associated with greater weight loss, particularly in females.