In healthy individuals, the upper GI tract (stomach, proximal small intestine) is a relatively sterile environment. Bacterial counts increase further down the GI tract (the middle and end of the small intestine) with the highest counts found in the colon. Small Intestinal Bacterial Overgrowth (SIBO) is a state of dysbiosis where there is an increase in the number of native or non-native bacteria within the small intestine. SIBO leads to excessive fermentation, inflammation, and malabsorption.

Some risk factors for developing SIBO include age (more common in elderly), low gastric acid, changes in anatomy (surgical resection of ileocecal valve), and altered motility. Symptoms typically include reflux, abdominal pain, bloating, diarrhea or constipation, and in severe cases, weight loss. SIBO can impair nutrient digestion and absorption if left untreated. One can present with deficiencies of B12, thiamine, niacin, iron, calcium, magnesium, and fat soluble vitamins (A,D,E). SIBO is typically diagnosed by a Hydrogen and/or Methane Breath Test, or by aspirate and culture of small bowel contents. It is not diagnosed by a stool sample. It is important to see a gastroenterologist (a doctor who specializes in diseases of the intestinal tract and liver) if you think you may have SIBO to ensure proper evaluation, diagnosis, and treatment, as SIBO can mimic other malabsorptive states such as celiac disease or pancreatitis.

If you have been diagnosed with SIBO, it is important to treat the overgrowth, identify and correct the underlying cause (if able), and take steps to prevent recurrence. SIBO treatment is typically based on gas produced as shown on the Breath Test (hydrogen and methane producers are treated differently) with broad spectrum antibiotics (such as rifaximin). Herbal antibiotics have also been used with success⁵, but larger studies are needed to determine safety and efficacy.

Once the overgrowth is treated, correcting the underlying cause is important to prevent recurrence. 44% of those who are successfully treated for SIBO will have a recurrence within 9 months⁷. Some underlying causes for SIBO can include IBD (with adhesive, stricturing disease, or fistulas), uncontrolled diabetes, diverticulosis, short bowel syndrome, use of narcotics which can slow motility, use of PPIs (proton pump inhibitors) to decrease gastric acid, and pancreatitis.

Altering diet is another way to help prevent recurrence of SIBO. The goals of nutrition therapy for SIBO are to reduce symptoms, improve digestion and absorption, manage weight, prevent recurrence, and correct nutrient imbalances. Although there is a lack of data to support a specific diet to treat SIBO, what we do know is:

• Reduced motility, an absent MMC (migrating motor complex) is a risk factor for SIBO⁸. We can help enhance the MMC by ensure fasting times between meals of 4-6 hours.
• —SIBO causes an injury of intestinal brush-border, affects disaccharidase activity. Limiting lactose can help counter this.
• A diet low in fermentable carbohydrates (such as fructose, sugar alcohols, lactose, legumes, and others) may help as these are fuel sources for bacteria
• Avoiding non-absorbable sugars such as sorbitol, sucralose, and saccharine can help improve flatus and bloating.
• Limiting aerophagia or air ingestion (chew with mouth closed, avoid carbonated beverages, gums/mints, and using straws) can help improve abdominal distention
• Bacteria can deconjugate bile acids, leading to fat maldigestion/malabsorption

My clinical experience has shown that modifying carbohydrates (grains, sugar, fruits, milk) may help as these foods are the primary fuel source for intestinal bacteria. Some real-food diets that have been proposed for managing SIBO are: the Low Fermentation diet (Cedars-Sinai diet), the low FODMAP diet, and the SCD or Specific Carbohydrate diet. There is evidence⁹ that supports the use of an elemental formula diet to help normalize gas production. Some downsides are that the formula can be difficult to drink, it is costly, and can negatively impact social life.

Some of these diets can be very restrictive and further complicate nutrient adequacy, leading to increased risk or worsening of malnutrition. It is important to work with a dietitian who specializes in SIBO to help find the best diet for your condition and help you implement diet changes in a healthy, balanced way.

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References:

1. Vanderhoof, J.A., & Pauley-Hunter, R.J. (2015). Etiology and pathogenesis of small intestinal bacterial overgrowth. UpToDate. Topic last updated January 6, 2015.
2. Bures, J., Cyrany, J., Kohoutova, D., Förstl, M., Rejchrt, S., Kvetina, J., Vorisek,V, & Kopacova, M. (2010). Small intestinal bacterial overgrowth syndrome. World Journal of Gastroenterology, 16(24), 2978-2990.
3. Bohm, M., Siwiec, R.M., & Wo, J.M. (2013). Diagnosis and management of small intestinal bacterial overgrowth. Nutrition in Clinical Practice, 28(3), 289-299.
4. Rezaie, A., Pimentel, M., & Rao, S. (2016). How to test and treat small intestinal bacterial overgrowth: an evidence based approach. Curr Gastroenterol Rep. 18(8), 1-11.
5. Chedid V, Dhalla S, Clarke JO, et al. (2014). Herbal therapy is equivalent to
   rifaximin for the treatment of small intestinal bacterial overgrowth.
   Glob Adv Health Med. 3:16–24.
6. Pimentel, M. (2015). Treatment of small intestinal bacterial overgrowth. UpToDate. Topic last updated November 16, 2015.
7. —Lauritano, EC, Maurizio, G, Scarpellini E, Lupascu, A, Novi, M, Sottilli, S, Vitale, G, Cesario, V, Serricchio, M, Cammarota, G, Gasbarrini, G, Gasbarrini, A. (2008). Small Intestinal Bacterial Overgrowth Recurrence After Antibiotic Therapy. American Journal of Gastroenterology. 103(8), 2031-2035.
8. —Jacobs C, Coss Adame E, Attaluri A, et al. (2013). Dysmotility and proton pump inhibitor use are independent risk factors for small intestinal bacterial overgrowth and/or fungal overgrowth. Aliment Pharmacol Ther., 37, 1103-1111.
9. Pimentel et al. (2004). A 14-day elemental diet is highly effective in normalizing the lactulose breath test. Dig Dis Sci. 49(1), 73-77.