Small intestinal bacterial overgrowth (SIBO) is characterized by an overgrowth of bacteria in the small intestine.
SIBO is diagnosed in someone who is symptomatic when a significant number of bacteria is present, as determined by small intestine culture or hydrogen breath testing with glucose or lactulose.
Common SIBO culprits are gram-negative species, typically found in the colon, that convert fermentable carbohydrates into hydrogen gas. Hydrogen gas can also be converted to methane by microorganisms, and methane can be measured as well (Pimentel 2020).
Besides colonic bacteria, oropharyngeal strains are also associated with SIBO. One study using small intestine culture revealed the most predominant strains retrieved included Streptococcus, Escherichia coli, Staphylococcus, Micrococcus, Klebsiella, Proteus for microaerophilic bacteria, and Lactobacillus, Bacteroides, Clostridium, Veillonella, Fusobacterium and Peptostreptococcus for anaerobic bacteria (Bouhnik 1999).
Risk factors for SIBO include proton pump inhibitor use, hypochlorhydria, chronic pancreatitis, cirrhosis, motility or GI anatomical disorders, diabetes, hypothyroidism, neuropathy, celiac disease, and immune disorders (Bushyhead 2021).
Protective factors that may be compromised in SIBO include gastric acid, pancreatic enzymes, bile acids, secretory IgA, motility, and the migrating motor complex (Chedid 2014).
Symptoms of SIBO may be related to increased intestinal permeability, malabsorption, inflammation, and immune activation. They can include nausea, excess gas, bloating, abdominal pain, diarrhea, constipation (with methane-producing microbes), weight loss, anemia, and nutrient deficiencies (Pimentel 2020).
SIBO can also increase the absorption of toxins and release of proinflammatory cytokines as it disrupts epithelial tight junctions and increases intestinal permeability. Additional manifestations of SIBO may include rosacea, arthralgias, interstitial cystitis, polyneuropathy, and fatty liver disease (Chedid 2014).
SIBO appears to be common in irritable bowel syndrome (IBS) and should be part of a comprehensive IBS workup. SIBO can also occur with disorders or medications that reduce motility and the natural movement of bacteria out of the small intestine. Although antibiotics have been routinely used to eradicate SIBO, potential consequences include adverse reactions, recurrence of infection, and growth of resistant or opportunistic bacteria. The presence of bile acids can enhance antimicrobial action (Bushyhead 2021).
SIBO can be common in diabetes, particularly if delayed gastric emptying and neuropathy are present. In one small study, SIBO was diagnosed in 43% of diabetic patients suffering from chronic diarrhea that improved significantly with antibiotic therapy (Salem 2014).
Symptoms of SIBO may be present in a number of conditions as well and should be investigated further. Disorders that increase the risk of concurrent SIBO include celiac, Crohn’s, IBS, short bowel syndrome, fatty liver disease, cirrhosis, pancreatic insufficiency, achlorhydria, fibromyalgia, connective tissue disorders, Parkinson’s, immune deficiency, and radiation enteritis.
Nutrient deficiencies related to SIBO should be evaluated, including fat-soluble vitamins A, D, E, K, B1, B3, B12, and iron. Malabsorption of fat and protein may occur as well (Salem 2014). Invading bacteria consume undigested food and even compete with the host for nutrients, further contributing to symptoms and deficiencies.
Brain fog may be seen with SIBO and includes difficulty concentrating, mental confusion, impaired judgment, and compromised short-term memory. This phenomenon may be associated with metabolic acidosis and elevated D-lactic acid, possibly due to the use of probiotics in some individuals (Rao 2018).
The use of probiotics for SIBO is debated as they may precipitate or exacerbate the condition. However, a meta-analysis of studies utilizing probiotics in SIBO found that probiotics alone effectively decontaminated the small intestine in 53.2-62.8% of SIBO cases, an effect enhanced by antibiotics, with the combination increasing decontamination to 85.8%. Probiotic species included Bifidobacterium, Bacillus clausii, Lactobacillus, S. boulardii, and mixed regimens. The analysis also found that probiotics were associated with improved abdominal pain and decreased hydrogen gas concentration, although they were ineffective in preventing SIBO (Zhong 2017). Probiotics may help prevent bacterial translocation and reduce bacterial endotoxins in the bloodstream as well (Twardowska 2022).
Some research reveals a reduction in SIBO GI symptoms with specific probiotics, including Saccharomyces boulardii, a probiotic yeast (Nickles 2021). Small studies have found some benefits in SIBO with the use of Bacillus clausii, L. casei, L. acidophilus, and Bacillus coagulans (Chen 2014, Khalighi 2014). Earlier studies found L. plantarum 299v and Lactobacillus (rhamnosus) GG to be beneficial in children with SIBO, especially those with short bowel syndrome (Vanderhoof 2001). Ultimately, probiotic therapy should be individualized and discontinued if symptoms worsen.
SIBO may promote or exacerbate histamine intolerance due to increased histamine production by GI bacteria or if less diamine oxidase (DAO) is available due to intestinal damage (Eade 2018, Schnedl 2021). Consuming supplemental DAO may reduce the histamine burden.
Dietary changes and herbal antimicrobials may be an alternative (or adjunct) to antibiotics for SIBO. Restriction of fermentable oligo-, di-, mono-saccharides, and polyol sugar alcohols (FODMAPs) may reduce symptoms and the amount of gas produced while SIBO is active (Pimentel 2020, Tuck 2018). An elemental diet is easily absorbed, can further restrict the “food” available to the problematic bacteria, and might be the most beneficial in severe cases.
Natural anti-microbial are effective against SIBO. In a retrospective chart review of 104 symptomatic individuals with a positive lactulose breath test, herbal antimicrobials were not only as effective as the antibiotic rifaximin but normalized breath tests in some of the subjects who had failed rifaximin. Subjects had a choice of either Biotics Dysbiocide plus FC Cidal, Metagenics Candibactin-AR plus Candibactin-BR, or rifaximin (Chedid 2014).
Natural Antimicrobials for SIBO include (Kohlstadt 2012, Chedid 2014, Wright 2021, Nickles 2021, Brown 2016, Salem 2014):
Choose 1 plan from the options below or combine
These restricted diets are to be used short-term while SIBO is active and symptoms are present. Guidance from a nutrition professional is recommended.
Choose 1 of the options below. To be taken for four consecutive weeks, 30 minutes before a meal.
Protocols for SIBO should be used in the short term while SIBO is active, but they can be modified for maintenance as needed.
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