Purpose: There is a scarcity of data on body composition changes after the two most widely performed bariatric procedures -- laparoscopic sleeve gastrectomy (SG) and laparoscopic Roux-en-Y gastric bypass (RYGB). The objective of this study was to analyse the changes in body composition between these two procedures during the first year after surgery. Methods: A prospective cohort study was performed in patients undergoing bariatric surgery at two tertiary hospitals between 2017 and 2023. Body composition was assessed with dual-energy X-ray absorptiometry immediately before surgery, and at 1, 6, 12, 18 and 24 months post-operatively. Total weight loss (TWL), excess weight loss (EWL), body mass index (BMI), fat mass (FM), lean body mass (LBM) and bone mineral content (BMC) parameters across the study period were compared between SG and RYGB. Results: Forty-five patients were included (RYGB n = 30, SG n = 15). There was a significant reduction in mean %TWL of 26.94 ± 8.86% and mean BMI of 11.12 ± 3.70 kg/m2 over 12 months. LBM accounted for 17.8% of TWL over 12 months, SG and RYGB did not differ in terms of loss of FM or LBM. For both procedures, the loss of LBM appeared to plateau at 6 months post-operatively. The only statistically significant finding between the two procedures was that RYGB resulted in an additional 0.06 kg loss compared with SG. Conclusion: LSG and LRYGB were shown to have comparable body composition changes in the short-to-medium term period following surgery. Given that there is a significant reduction in LBM which predominantly occurs in the early post-operative period, further research is warranted to implement a structured exercise and nutritional program during this window to mitigate LBM losses.