BACKGROUND: Weight loss after sleeve gastrectomy (SG) demonstrates significant diversity in the long term and the implicated mechanisms behind suboptimal clinical response (SCR) or recurrent weight gain (RWG) need to be scrutinized. This study retrospectively examines weight-loss trajectories, aiming to identify critical time points to optimize follow-up strategies and guide future prospective research. METHODS: This is a single-center, retrospective study of 104 patients that underwent SG. Excess body weight loss (%EWL) was calculated at 1, 3, 6, 12, 24, 60, and at 160.4 ± 16 months, while RWG was defined as the difference between the body mass index (BMI) at evaluation and the minimum BMI achieved postoperatively. In accordance with the clinical response, patients were classified into good responders (Group A: %EWL ≥ 50 and RWG <
5 kg/m RESULTS: In the first postoperative month good responders achieved the highest %EWL 24.4 ± 6.5, compared to the other two groups (p <
0.05). After 24 months, all patients showed a decrease in %EWL, with good and partial responders following the same pattern until the fifth year. After the fifth year, EWL% was significantly decreased in partial responders (p = 0.014), while in good responders it remained relatively unchanged (p = 0.159). CONCLUSION: The first postoperative month and the fifth postoperative year have been identified as potential critical periods for determining long-term clinical outcomes.