Prevalence of Nutrient Deficiencies Following Bariatric Surgery—Long-Term, Prospective Observation

<b>Background/Objectives</b>: To estimate the long-term prevalence of the most common nutrient deficiencies following bariatric surgery. <b>Methods</b>: Consecutive patients who underwent bariatric surgery were followed for 10 years. Anthropometric measurements, laboratory tests, and comorbidities were assessed at baseline and during follow-up visits. <b>Results</b>: A total of 155 patients were included (74.2% women; mean age 43.6 ± 9.3 years; mean body mass index [BMI]: 41.9 kg/m²). Patients underwent either sleeve gastrectomy (SG, <i>n</i> = 112) or gastric bypass (GB, <i>n</i> = 43). Over a median follow-up period of 10 (10-12) years, BMI decreased by 7.4 ± 5.8 kg/m². In the GB group, serum iron levels decreased significantly, whereas in the SG group, a reduction was observed in total iron-binding capacity (TIBC). Serum calcium, phosphorus, and 25-hydroxyvitamin D3 levels increased during follow-up. The prevalence of deficiencies in iron (9.0% vs. 18.7%, <i>p</i> < 0.05), folic acid (1.3% vs. 11.6%, <i>p</i> < 0.001), and vitamin B12 (7.1% vs. 17.4%, <i>p</i> < 0.01) increased, while the prevalence of hypocalcemia and 25-hydroxyvitamin D3 deficiency decreased. <b>Conclusions</b>: A significant increase in the prevalence of iron, folic acid, and vitamin B12 deficiencies was observed over a 10-year follow-up after bariatric surgery. SG and GB appear to have different long-term effects on iron metabolism.