Pre- and Postoperative Nutritional Deficiencies in Patients Undergoing Bariatric Surgery: A Retrospective Cohort Study

AIM: To assess the changes in biochemical indicators of nutritional deficiencies before and after bariatric surgery. METHODS: This retrospective cohort study included 480 adult patients who underwent bariatric surgery between June 2016 and June 2019 at a tertiary care center in Saudi Arabia. Demographic data, comorbidities, and pre- and postoperative biochemical parameters, including hemoglobin, iron profile, Vitamin D, Vitamin B12, albumin, calcium, and parathyroid hormone levels, were extracted from the medical records. These biochemical parameters were used to assess micronutrient status and identify clinically relevant nutritional deficiencies based on established laboratory thresholds. Paired t- and McNemar tests were used to compare the pre- and postoperative values. Statistical significance was set at p < 0.05. RESULTS: We found a high prevalence of pre- and postoperative nutritional deficiencies among patients. The mean hemoglobin decreased from 13.09 to 12.34 g/dL (mean difference –0.75 g/dL; 95% CI –0.89 to –0.61; p < 0.001). We observed a significant association between ferritin and gender pre- and postoperatively, which was lower in women than in men preoperatively and decreased in both sexes postoperatively. The prevalence of 25-hydroxyvitamin D deficiency was 88.0% preoperatively and 72.7% postoperatively in patients with available laboratory data. CONCLUSIONS: A high prevalence of pre- and postoperative nutritional deficiencies was observed among patients undergoing bariatric surgery in Saudi Arabia. Although certain parameters improved after surgery, others remained prevalent or worsened postoperatively. These findings highlight the importance of structured nutritional assessments and regular biochemical monitoring before and after bariatric surgery.