Background <p>Despite the growing adoption of bariatric surgery (BS) in China, data on its nutritional impacts remain limited. This study aimed to investigate the nutritional status of Chinese patients at 1 year post-BS.</p> Method <p>A retrospective analysis of 562 patients treated between January 2022 and January 2023 was conducted, with 231 patients completing 12-month follow-ups. Baseline and postoperative data on anthropometrics, metabolism and nutrition were gathered at 1, 3, 6 and 12 months.</p> Results <p>Preoperative vitamin D deficiency was most prevalent (77.1%), followed by ferritin (9.5%), folate (3.0%), vitamin B12 (2.2%), anemia (2.2%) and albumin (0.4%). Compared to baseline, the serum levels of albumin, folate and 25-hydroxyvitamin D [25 (OH) D] increased throughout the first postoperative year, while hemoglobin and ferritin declined at 12 months (<i>P</i> &lt; 0.05). Anemia and ferritin deficiency rates increased to 11.7% and 33.8% at 12 months post-operation, respectively, while folate deficiency decreased to 0.4% (<i>P</i> &lt; 0.05). Non-compliance with multivitamin supplementation demonstrated significantly higher prevalence of vitamin D deficiency (70.7% vs. 52.6%), iron deficiency (58.6% vs. 25.4%) and anemia (20.7% vs. 8.7%) compared to regularly supplemented counterparts (all <i>P</i> &lt; 0.05). Multivariable linear regression revealed preoperative hemoglobin, ferritin and 25 (OH) D levels were independent predictors of 12-month postoperative changes in their corresponding nutrients.</p> Conclusion <p>Despite improved body composition and metabolism, postoperative nutritional deficiencies remain common. Routine preoperative nutritional assessment and long-term postoperative monitoring are essential for nutritional balance.</p> <p>Keywords: Bariatric surgery; Nutritional status; Micronutrients; Supplement adherence</p>