April 2020 Issue

Ask the Expert: An Update on SIBO
By Toby Amidor, MS, RD, CDN, FAND
Today’s Dietitian
Vol. 22, No. 4, P. 10

Q: What are the current guidelines for diagnosis and nutritional management of small intestinal bacterial overgrowth (SIBO)?

A: To date, there are no gold-standard diagnostic tests or dietary management strategies for SIBO, but RDs can stay abreast of methods presently in use and learn how to be an effective member of a client’s treatment team. The following is a primer on SIBO and the most up-to-date recommendations for RDs counseling clients and patients with the condition.

What Is SIBO?
SIBO is characterized by the presence of excessive bacteria in the small intestine.1 That said, there’s no consensus on the definition of SIBO, most likely due to the lack of a gold standard for diagnosis and the condition’s nonspecific symptoms. According to Kate Scarlata, MPH, RDN, a gut health expert who specializes in irritable bowel syndrome (IBS) and coauthor of The Low-FODMAP Diet Step by Step, “SIBO symptoms often mimic those of IBS, but, I might argue, tend to be more severe.” Symptoms of SIBO include significant bloating, postprandial fullness, altered bowel habits such as diarrhea and/or constipation, excess flatulence, and, in some cases, steatorrhea due to fat maldigestion and malabsorption.

Clients may present with weight loss and/or altered micronutrient levels due to adverse consequences of bacterial overgrowth. “Some microbes in the small bowel deconjugate bile acids, which can result in fat malabsorption,” Scarlata says. Poor absorption of fat can lead to deficiencies of fat-soluble nutrients such as vitamins A, D, and E.

According to Emily Haller, MS, RDN, a dietitian in the division of gastroenterology at Michigan Medicine in Ann Arbor, risk factors for SIBO may include altered anatomy (eg, small bowel diverticulosis, resection of the ileo-cecal valve, or gastric bypass), hypochlorhydria due to gastritis, or small bowel dysmotility, which can occur in inflammatory bowel disease, radiation enteritis, postinfectious IBS, or as a result of scleroderma and/or diabetes.

While there’s no gold-standard test to diagnose SIBO, a breath test that quantifies hydrogen and methane currently is the most widely used method; however, its accuracy has been questioned in the literature. A small bowel aspiration and culture can be conducted during an endoscopy, but it may miss distal small bowel bacteria overgrowth and thus typically isn’t done in clinical practice. Scarlata says elevated serum folate levels in the absence of supplementation (ie, due to bacterial synthesis) and a reduced level of vitamin B12 (ie, due to inhibition of normal B12 absorption by anaerobic organisms in the terminal ileum) may be further evidence for an SIBO diagnosis.

Haller says more SIBO testing options are emerging, including using small bowel samples to screen for volatile organic compounds and measuring hydrogen sulfite in the breath.

Recommendations for Clients
According to Haller, “The mainstay of SIBO management is antibiotic therapy, and rifaximin is currently the most thoroughly studied antibiotic for SIBO treatment. However, diet can help lessen symptoms and improve quality of life, oral intake, and nutrition status.” Both Scarlata and Haller recommend following a low-FODMAP diet, which has been shown anecdotally to offer relief from SIBO symptoms. Furthermore, to be an effective member of the treatment team, RDs should do the following when counseling clients with SIBO:

• Screen for maladaptive or disordered eating. Scarlata says this is more common in clients with gastrointestinal disorders than among individuals without such conditions.

• Avoid creating food fears. Many clients with SIBO may try self-guided elimination diets, which can result in severe food restriction, with clients avoiding more foods than they eat. “While [RDs] can use dietary strategies to improve symptoms, it’s important to avoid creating or worsening food fears and help patients achieve a balanced diet they tolerate,” Haller says.

• Identify and treat predisposed conditions, when applicable. Haller says RDs may encounter clients with untreated conditions such as celiac disease or diabetic enteropathy in addition to SIBO. These conditions should be treated before addressing SIBO.

• Recommend eating discrete meals vs several small meals or “grazing.” According to Scarlata, there may be some benefit to eating discrete meals, and fasting in between them, as these breaks can enable the migrating motor complex to initiate a cleansing wave between eating times (which helps sweep residual bacteria, food, and secretions from the small intestine), thus reducing SIBO risk.

• Work with a gastroenterologist or primary care provider. Communicate with the clients’ physician regarding test results, medical treatments, and predisposing conditions when feasible, such as the use of motility agents or cessation of opiates or proton pump inhibitors.

— Toby Amidor, MS, RD, CDN, FAND, is the founder of Toby Amidor Nutrition (http://tobyamidornutrition.com) and a Wall Street Journal best-selling author. Her cookbooks include Smart Meal Prep for Beginners, The Easy 5-Ingredient Healthy Cookbook, The Healthy Meal Prep Cookbook, The Greek Yogurt Kitchen, and the upcoming The Best Rotisserie Chicken Cookbook and The Create-Your-Plate Diabetes Cookbook. She’s a nutrition expert for FoodNetwork.com and a contributor to U.S. News Eat + Run and Muscle&Fitness.com.

1. Adike A, DiBaise JK. Small intestinal bacterial overgrowth: nutritional implications, diagnosis, and management. Gastroenterol Clin North Am. 2018;47(1):193-208.