Human Small Intestinal Absorption Following Gastric Bypass Surgery

Abstract

Gastric bypass surgery (GBS) produces a relatively achlorhydric state by formation of a small cardia-fundal pouch with a gastro-jejunal anastomosis. Small intestinal bacterial overgrowth (SIBO) is known to alter vitamin B12 absorption. It has been proposed that gastric acid secretion prevents SIBO. We hypothesized that GBS alters small intestinal micronutrient absorption. This is a retrospective review of patients who underwent Roux-en-Y GBS from 1999-2005. Postoperative patients underwent glucose-hydrogen breath testing to examine upper intestinal (jejunal) bacterial production of methane and hydrogen. Patients’ sex, age, and whole blood thiamine diphosphate levels were obtained 6 months after GBS. Abnormal glucose-hydrogen breath test was defined by fasting breath hydrogen/methane >10 ppm or increased hydrogen/methane of >20 ppm within 60 minutes after 50 grams oral glucose. There were 32 females & 4 males (mean age 47 years; range 22 to 65). All 36 had abnormal glucose-hydrogen breath tests. Thirty-two patients (89%) were hydrogen producers & 13 patients (36%) produced methane; 26 patients (72%) had whole blood thiamine levels below the lower limit of normal. CONCLUSION: This study supports the idea that gastric acid secretion prevents SIBO. Since 72% of GBS patients had low thiamine levels, micronutrient absorption is altered after GPS. Present physiological evidence supports the presence of a saturable, carrier-mediated exchange mechanism for thiamine transport across human jejunum; therefore, SIBO may alter this carrier-mediated mechanism.