Introduction <p>Bariatric surgery effectively induces weight loss, yet its impact on micronutrient homeostasis, particularly zinc, remains unclear. Given zinc’s essential role in wound healing, immunity, and hair growth, understanding postoperative changes is clinically relevant. This study evaluated the effect of sleeve gastrectomy and one-anastomosis gastric bypass on serum zinc levels.</p> Methods <p>The prospective cohort study recruited 50 patients with severe obesity who underwent bariatric surgery. Patients were divided to two groups and monitored for one year. Laparoscopic sleeve gastrectomy group included 25 participants; one anastomosis gastric bypass surgery group included 25 participants. Primary outcome was the assessment of serum zinc levels at 3, 6, and 12 months postoperatively. Secondary outcomes included the incidence of symptoms associated with reduced zinc levels, such as hair loss, diarrhea, and delayed wound healing.</p> Results <p>Patients who underwent one-anastomosis single bypass surgery had a higher incidence of low serum zinc levels at 6 months and at 12 months postoperatively compared to those who underwent sleeve gastrectomy (60.5 ± 20.9 vs. 79.8 ± 19.1 µg/dL, <i>p</i> = 0.008, and 49.7 ± 19.1 vs. 79.2 ± 22.8 µg/dL, <i>p</i> &lt; 0.001). Symptoms related to hypozincemia, including hair loss, diarrhea and delayed wound healing, were significantly increased after one-anastomosis single bypass surgery (<i>p</i> ˂ 0.05).</p> Conclusion <p>One-anastomosis single bypass is associated with a higher postoperative incidence of hypozincemia, as well as a worsening of symptoms compared to sleeve gastrectomy.</p>