Treatment of Symptomatic Small Intestinal Bacterial Overgrowth and Weight Gain after Gastric Bypass Surgery

Abstract

Purpose: We reported that daily oral thiamine is not effective for treating thiamine deficiency after Roux-en-Y gastric bypass surgery (GPS); in contrast, in those patients with abnormal glucose-hydrogen breath tests, antibiotic therapy with oral thiamine is effective therapy. Small intestinal bacterial overgrowth (SIBO) interferes with micronutrient and macronutrient absorption from the small intestine and may reduce caloric intake. We hypothesize that antibiotic therapy for SIBO induces weight gain after GBS. Methods: In this retrospective chart review; 17 female patients (age range 33–65 years; mean age 51 years) had Roux-en-Y GBS in 1999–2005. The study included: 1) post-operative patients who had both an abnormal glucose-hydrogen breath test and abdominal symptoms consistent with SIBO, who 2) received an antibiotic to treat bacterial overgrowth. Antibiotic was given for 7 to 10 days, once monthly. Sex, age, weight before and after receiving antibiotic, and the presence of or resolution of abdominal symptoms after antibiotic were recorded. Abnormal glucose-hydrogen breath test was defined by increase in breath hydrogen >20 ppm within 45 minutes after 50 grams glucose. Patients were seen 8 to 72 months after GBS (mean: 32 months). Resolution of abdominal symptoms was used to determine effectiveness of antibiotic therapy. Results: Eight patients had weight gain (range: 0.5–7.2 kg; mean: 3.2 kg) 2 to 5 months (mean: 3.1 months) after beginning antibiotic therapy. Among these 8 patients, abdominal symptoms resolved in 7; among 9 patients with weight loss, only 3 had resolution of abdominal symptoms (Chi-squared 2×2: P= .03). Nine patients had weight loss of 0.5 to 14.4 kg (mean: 4.6 kg) at 2 to 4 months (mean: 3.1 months). Abdominal symptoms resolved in 7 of 13 patients receiving metronidazole, 1 of 2 with amoxicillin/clavulanate, and 2 of 2 with rifaximin. Conclusion: Weight gain in patients with SIBO receiving antibiotics was associated with resolution of abdominal symptoms. This supports our hypothesis that antibiotic treatment of bacterial overgrowth induces weight gain. Conversely, SIBO may promote weight loss after GBS. Weight gain noted after antibiotic treatment could be due to: increased caloric intake, resolution of abdominal symptoms, or increased macronutrient absorption.